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- Nullreferenceexception Object Reference Not Set To An Instance Of An Object
- Nullreferenceexception Object Reference Not Set To An Instance Of An Object Rust
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- What is a NullReferenceException, and how do I fix it? 31 answers
I am receiving this error and I'm not sure what it means?
Object reference not set to an instance of an object.
John Saunders149k2222 gold badges207207 silver badges369369 bronze badges
mohammad rezamohammad reza1,16466 gold badges1919 silver badges3737 bronze badges
marked as duplicate by Bill the LizardDec 23 '14 at 19:41
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
8 Answers
Variables in .NET are either reference types or value types. Value types are primitives such as integers and booleans or structures (and can be identified because they inherit from System.ValueType). Boolean variables, when declared, have a default value:
Reference types, when declared, do not have a default value:
If you try to access a member of a class instance using a null reference then you get a System.NullReferenceException. Which is the same as Object reference not set to an instance of an object.
The following code is a simple way of reproducing this:
This is a very common error and can occur because of all kinds of reasons. The root cause really depends on the specific scenario that you've encountered.
If you are using an API or invoking methods that may return null then it's important to handle this gracefully. The main method above can be modified in such a way that the NullReferenceException should never be seen by a user:
All of the above really just hints of .NET Type Fundamentals, for further information I'd recommend either picking up CLR via C# or reading this MSDN article by the same author - Jeffrey Richter. Also check out, much more complex, example of when you can encounter a NullReferenceException.
Some teams using Resharper make use of JetBrains attributes to annotate code to highlight where nulls are (not) expected.
Community♦
IainIain6,6131616 gold badges4949 silver badges5858 bronze badges
JayJay11.1k33 gold badges3030 silver badges6060 bronze badges
In a nutshell it means. You are trying to access an object without instantiating it. You might need to use the 'new' keyword to instantiate it first i.e create an instance of it.
For eg:
You will have to use:
Hope I made it clear.
Adithya KumaranchathAdithya Kumaranchath
Not to be blunt but it means exactly what it says. One of your object references is NULL. You'll see this when you try and access the property or method of a NULL'd object.
dkpattdkpatt
It means you did something like this.
And without doing
if(myObject!=null)
, you go ahead do myObject.Method();
16.9k1616 gold badges7979 silver badges133133 bronze badges
J.W.J.W.13.8k55 gold badges3737 silver badges6868 bronze badges
Most of the time, when you try to assing value into object, and if the value is null, then this kind of exception occur.Please check this link.
for the sake of self learning, you can put some check condition. like
Syed Tayyab AliSyed Tayyab Ali2,61166 gold badges2525 silver badges3535 bronze badges
what does this error mean? Object reference not set to an instance of an object.
exactly what it says, you are trying to use a null object as if it was a properlyreferenced object.
TStamperTStamper26.8k1010 gold badges5858 silver badges7070 bronze badges
If I have the class:
and I then do:
The second line throws this exception becuase I'm calling a method on a reference type object that is
LiamLiamnull
(I.e. has not been instantiated by calling myClass = new MyClass()
)16.9k1616 gold badges7979 silver badges133133 bronze badges
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I have been getting an error in VB.net 'object reference not set to an instance of object'. Can you tell me what are the causes of this error? thanks.
John Saunders149k2222 gold badges207207 silver badges369369 bronze badges
sefsef1,86266 gold badges1818 silver badges2323 bronze badges
8 Answers
sef,If the problem is with Database return results, I presume it is in this scenario:
To fix that:
edit: added code formatting tags ..
torialtorial10.9k99 gold badges5555 silver badges8888 bronze badges
The object has not been initialized before use.
At the top of your code file type:
NescioNescio23.1k1010 gold badges4848 silver badges6969 bronze badges
Let's deconstruct the error message.
'object reference' means a variable you used in your code which referenced an object. The object variable could have been declared by you the or it you might just be using a variable declared inside another object.
'instance of object' Means that the object is blank (or in VB speak, 'Nothing'). When you are dealing with object variables, you have to create an instance of that object before referencing it.
'not set to an ' means that you tried to access an object, but there was nothing inside of it for the computer to access.
If you create a variable like
All you have done was tell the compiler that aPerson will represent a person, but not what person.
You can create a blank copy of the object by using the 'New' keyword. For example
If you want to be able to test to see if the object is 'nothing' by
Hope that helps!
Andrew NeelyAndrew Neely
In general, under the .NET runtime, such a thing happens whenever a variable that's unassigned or assigned the value
Nothing
(in VB.Net, null
in C#) is dereferenced.Option Strict On
and Option Explicit On
will help detect instances where this may occur, but it's possible to get a null/Nothing from another function call:and the NullReferenceException is the source of the 'object reference not set to an instance of an object'.
Blair ConradBlair Conrad162k2424 gold badges121121 silver badges105105 bronze badges
And if you think it's occuring when no data is returned from a database query then maybe you should test the result before doing an operation on it?
Mark GlorieMark Glorie3,00222 gold badges2323 silver badges3131 bronze badges
You can put a logging mechanism in your application so you can isolate the cause of the error. An Exception object has the StackTrace property which is a string that describes the contents of the call stack, with the most recent method call appearing first. By looking at it, you'll have more details on what might be causing the exception.
Leon TaysonLeon Tayson3,38855 gold badges3131 silver badges3535 bronze badges
When working with databases, you can get this error when you try to get a value form a field or row which doesn't exist. i.e. if you're using datasets and you use:
you get the object 'reference not set to an instance of object' if tablename doesn't exists in the Dataset. The same for rows or fields in the datasets.
Eduardo CampañóEduardo Campañó5,69144 gold badges2323 silver badges2323 bronze badges
Well, Error is explaining itself. Since You haven't provided any code sample, we can only say somewhere in your code, you are using a Null object for some task. I got same Error for below code sample.
As You can see I am going to Clear a Null Object. For that, I'm getting Error
'object reference not set to an instance of an object'
Check your code for such code in your code. Since you haven't given code example we can't highlight the code :)
Menuka IshanMenuka Ishan
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I have some code and when it executes, it throws a
NullReferenceException
, saying:Object reference not set to an instance of an object.
What does this mean, and what can I do to fix this error?
locked by Bhargav Rao♦Dec 19 '17 at 6:38
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31 Answers
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Bottom Line
You are trying to use something that is
null
(or Nothing
in VB.NET). This means you either set it to null
, or you never set it to anything at all. Like anything else,
null
gets passed around. If it is null
in method 'A', it could be that method 'B' passed a null
to method 'A'.null
can have different meanings:- Object variables which are uninitialized and hence point to nothing. In this case, if you access properties or methods of such objects, it causes a
NullReferenceException
. - The developer is using
null
intentionally to indicate there is no meaningful value available. Note that C# has the concept of nullable datatypes for variables (like database tables can have nullable fields) - you can assignnull
to them to indicate there is no value stored in it, for exampleint? a = null;
where the question mark indicates it is allowed to store null in variablea
. You can check that either withif (a.HasValue) {..}
or withif (anull) {..}
. Nullable variables, likea
this example, allow to access the value viaa.Value
explicitly, or just as normal viaa
.
Note that accessing it viaa.Value
throws anInvalidOperationException
instead of aNullReferenceException
ifa
isnull
- you should do the check beforehand, i.e. if you have another on-nullable variableint b;
then you should do assignments likeif (a.HasValue) { b = a.Value; }
or shorterif (a != null) { b = a; }
.
The rest of this article goes into more detail and shows mistakes that many programmers often make which can lead to a
NullReferenceException
.More Specifically
The runtime throwing a
NullReferenceException
always means the same thing: you are trying to use a reference, and the reference is not initialized (or it was once initialized, but is no longer initialized). This means the reference is
null
, and you cannot access members (such as methods) through a null
reference. The simplest case:This will throw a
NullReferenceException
at the second line because you can't call the instance method ToUpper()
on a string
reference pointing to null
.How do you find the source of a
NullReferenceException
? Apart from looking at the exception itself, which will be thrown exactly at the location where it occurs, the general rules of debugging in Visual Studio apply: place strategic breakpoints and inspect your variables, either by hovering the mouse over their names, opening a (Quick)Watch window or using the various debugging panels like Locals and Autos.If you want to find out where the reference is or isn't set, right-click its name and select 'Find All References'. You can then place a breakpoint at every found location and run your program with the debugger attached. Every time the debugger breaks on such a breakpoint, you need to determine whether you expect the reference to be non-null, inspect the variable and and verify that it points to an instance when you expect it to.
By following the program flow this way, you can find the location where the instance should not be null, and why it isn't properly set.
Some common scenarios where the exception can be thrown:
Generic
If ref1 or ref2 or ref3 is null, then you'll get a
NullReferenceException
. If you want to solve the problem, then find out which one is null by rewriting the expression to its simpler equivalent:Specifically, in
HttpContext.Current.User.Identity.Name
, the HttpContext.Current
could be null, or the User
property could be null, or the Identity
property could be null.Indirect
If you want to avoid the child (Person) null reference, you could initialize it in the parent (Book) object's constructor.
Nested Object Initializers
The same applies to nested object initializers:
This translates to
While the
new
keyword is used, it only creates a new instance of Book
, but not a new instance of Person
, so the Author
the property is still null
.Nested Collection Initializers
![Set Set](/uploads/1/2/3/9/123947688/900177556.jpg)
The nested collection initializers behave the same:
This translates to
The
new Person
only creates an instance of Person
, but the Books
collection is still null
. The collection initializer syntax does not create a collectionfor p1.Books
, it only translates to the p1.Books.Add(..)
statements.Array
Array Elements
Jagged Arrays
Collection/List/Dictionary
Range Variable (Indirect/Deferred)
Events
Bad Naming Conventions:
If you named fields differently from locals, you might have realized that you never initialized the field.
This can be solved by following the convention to prefix fields with an underscore:
ASP.NET Page Life cycle:
ASP.NET Session Values
ASP.NET MVC empty view models
If the exception occurs when referencing a property of
@Model
in an ASP.NET MVC view, you need to understand that the Model
gets set in your action method, when you return
a view. When you return an empty model (or model property) from your controller, the exception occurs when the views access it:WPF Control Creation Order and Events
WPF controls are created during the call to
InitializeComponent
in the order they appear in the visual tree. A NullReferenceException
will be raised in the case of early-created controls with event handlers, etc. , that fire during InitializeComponent
which reference late-created controls.For example :
Here
comboBox1
is created before label1
. If comboBox1_SelectionChanged
attempts to reference `label1, it will not yet have been created.Changing the order of the declarations in the XAML (i.e., listing
label1
before comboBox1
, ignoring issues of design philosophy, would at least resolve the NullReferenceException
here.Cast with as
This doesn't throw an InvalidCastException but returns a
null
when the cast fails (and when someObject is itself null). So be aware of that.LINQ FirstOrDefault() and SingleOrDefault()
The plain versions
First()
and Single()
throw exceptions when there is nothing. The 'OrDefault' versions return null in that case. So be aware of that.foreach
foreach
throws when you try to iterate null collection. Usually caused by unexpected null
result from methods that return collections.More realistic example - select nodes from XML document. Will throw if nodes are not found but initial debugging shows that all properties valid:
Explicitly check for null
and ignore null values.
If you expect the reference sometimes to be null, you can check for it being
null
before accessing instance members:Explicitly check for null
and provide a default value.
Methods call you expect to return an instance can return
null
, for example when the object being sought cannot be found. You can choose to return a default value when this is the case:Explicitly check for null
from method calls and throw a custom exception.
You can also throw a custom exception, only to catch it in the calling code:
Use Debug.Assert
if a value should never be null
, to catch the problem earlier than the exception occurs.
When you know during development that a method maybe can, but never should return
null
, you can use Debug.Assert()
to break as soon as possible when it does occur:Though this check will not end up in your release build, causing it to throw the
NullReferenceException
again when book null
at runtime in release mode.Use GetValueOrDefault()
for nullable value types to provide a default value when they are null
.
Use the null coalescing operator: ??
[C#] or If()
[VB].
The shorthand to providing a default value when a
null
is encountered:Use the null condition operator: ?.
or ?[x]
for arrays (available in C# 6 and VB.NET 14):
This is also sometimes called the safe navigation or Elvis (after its shape) operator. If the expression on the left side of the operator is null, then the right side will not be evaluated, and null is returned instead. That means cases like this:
If the person does not have a title, this will throw an exception because it is trying to call
ToUpper
on a property with a null value.In C# 5 and below, this can be guarded with:
Now the title variable will be null instead of throwing an exception. C# 6 introduces a shorter syntax for this:
This will result in the title variable being
null
, and the call to ToUpper
is not made if person.Title
is null
.Of course, you still have to check
title
for null or use the null condition operator together with the null coalescing operator (??
) to supply a default value:Likewise, for arrays you can use
?[i]
as follows:This will do the following: If myIntArray is null, the expression returns null and you can safely check it. If it contains an array, it will do the same as:
elem = myIntArray[i];
and returns the ith element.Special techniques for debugging and fixing null derefs in iterators
C# supports 'iterator blocks' (called 'generators' in some other popular languages). Null dereference exceptions can be particularly tricky to debug in iterator blocks because of deferred execution:
If
whatever
results in null
then MakeFrob
will throw. Now, you might think that the right thing to do is this:Why is this wrong? Because the iterator block does not actually run until the
foreach
! The call to GetFrobs
simply returns an object which when iterated will run the iterator block.By writing a null check like this you prevent the null dereference, but you move the null argument exception to the point of the iteration, not to the point of the call, and that is very confusing to debug.
The correct fix is:
That is, make a private helper method that has the iterator block logic, and a public surface method that does the null check and returns the iterator. Now when
GetFrobs
is called, the null check happens immediately, and then GetFrobsForReal
executes when the sequence is iterated.If you examine the reference source for LINQ to Objects you will see that this technique is used throughout. It is slightly more clunky to write, but it makes debugging nullity errors much easier. Optimize your code for the convenience of the caller, not the convenience of the author.
A note on null dereferences in unsafe code
C# has an 'unsafe' mode which is, as the name implies, extremely dangerous because the normal safety mechanisms which provide memory safety and type safety are not enforced. You should not be writing unsafe code unless you have a thorough and deep understanding of how memory works.
In unsafe mode, you should be aware of two important facts:
- dereferencing a null pointer produces the same exception as dereferencing a null reference
- dereferencing an invalid non-null pointer can produce that exceptionin some circumstances
To understand why that is, it helps to understand how .NET produces null dereference exceptions in the first place. (These details apply to .NET running on Windows; other operating systems use similar mechanisms.)
Memory is virtualized in Windows; each process gets a virtual memory space of many 'pages' of memory that are tracked by the operating system. Each page of memory has flags set on it which determine how it may be used: read from, written to, executed, and so on. The lowest page is marked as 'produce an error if ever used in any way'.
Both a null pointer and a null reference in C# are internally represented as the number zero, and so any attempt to dereference it into its corresponding memory storage causes the operating system to produce an error. The .NET runtime then detects this error and turns it into the null dereference exception.
That's why dereferencing both a null pointer and a null reference produces the same exception.
What about the second point? Dereferencing any invalid pointer that falls in the lowest page of virtual memory causes the same operating system error, and thereby the same exception.
Why does this make sense? Well, suppose we have a struct containing two ints, and an unmanaged pointer equal to null. If we attempt to dereference the second int in the struct, the CLR will not attempt to access the storage at location zero; it will access the storage at location four. But logically this is a null dereference because we are getting to that address via the null.
If you are working with unsafe code and you get a null dereference exception, just be aware that the offending pointer need not be null. It can be any location in the lowest page, and this exception will be produced.
The
NullReference Exception
for Visual Basic is no different from the one in C#. After all, they are both reporting the same exception defined in the .NET Framework which they both use. Causes unique to Visual Basic are rare (perhaps only one).This answer will use Visual Basic terms, syntax, and context. The examples used come from a large number of past Stack Overflow questions. This is to maximize relevance by using the kinds of situations often seen in posts. A bit more explanation is also provided for those who might need it. An example similar to yours is very likely listed here.
Note:
- This is concept-based: there is no code for you to paste into your project. It is intended to help you understand what causes a
NullReferenceException
(NRE), how to find it, how to fix it, and how to avoid it. An NRE can be caused many ways so this is unlikely to be your sole encounter. - The examples (from Stack Overflow posts) do not always show the best way to do something in the first place.
- Typically, the simplest remedy is used.
Basic Meaning
The message 'Object not set to an instance of Object' means you are trying to use an object which has not been initialized. This boils down to one of these:
- Your code declared an object variable, but it did not initialize it (create an instance or 'instantiate' it)
- Something which your code assumed would initialize an object, did not
- Possibly, other code prematurely invalidated an object still in use
Finding The Cause
Since the problem is an object reference which is
Nothing
, the answer is to examine them to find out which one. Then determine why it is not initialized. Hold the mouse over the various variables and Visual Studio (VS) will show their values - the culprit will be Nothing
.You should also remove any Try/Catch blocks from the relevant code, especially ones where there is nothing in the Catch block. This will cause your code to crash when it tries to use an object which is
Nothing
. This is what you want because it will identify the exact location of the problem, and allow you to identify the object causing it.A
MsgBox
in the Catch which displays Error while..
will be of little help. This method also leads to very bad Stack Overflow questions, because you can't describe the actual exception, the object involved or even the line of code where it happens.You can also use the
Locals Window
(Debug -> Windows -> Locals) to examine your objects.Once you know what and where the problem is, it is usually fairly easy to fix and faster than posting a new question.
See also:
Examples and Remedies
Class Objects / Creating an Instance
The problem is that
Dim
does not create a CashRegister object; it only declares a variable named reg
of that Type. Declaring an object variable and creating an instance are two different things.Remedy
The
New
operator can often be used to create the instance when you declare it:When it is only appropriate to create the instance later:
Note: Do not use
Dim
again in a procedure, including the constructor (Sub New
):This will create a local variable,
reg
, which exists only in that context (sub). The reg
variable with module level Scope
which you will use everywhere else remains Nothing
.Missing the
New
operator is the #1 cause of NullReference Exceptions
seen in the Stack Overflow questions reviewed.Visual Basic tries to make the process clear repeatedly using
New
: Using the New
Operator creates a new object and calls Sub New
-- the constructor -- where your object can perform any other initialization.To be clear,
Dim
(or Private
) only declares a variable and its Type
. The Scope of the variable - whether it exists for the entire module/class or is local to a procedure - is determined by where it is declared. Private | Friend | Public
defines the access level, not Scope.For more information, see:
Arrays
Arrays must also be instantiated:
This array has only been declared, not created. There are several ways to initialize an array:
Note: Beginning with VS 2010, when initializing a local array using a literal and
Option Infer
, the As <Type>
and New
elements are optional:The data Type and array size are inferred from the data being assigned. Class/Module level declarations still require
As <Type>
with Option Strict
:Example: Array of class objects
The array has been created, but the
Foo
objects in it have not.Remedy
Using a
List(Of T)
will make it quite difficult to have an element without a valid object:For more information, see:
Lists and Collections
.NET collections (of which there are many varieties - Lists, Dictionary, etc.) must also be instantiated or created.
You get the same exception for the same reason -
myList
was only declared, but no instance created. The remedy is the same:A common oversight is a class which uses a collection
Type
:Either procedure will result in an NRE, because
barList
is only declared, not instantiated. Creating an instance of Foo
will not also create an instance of the internal barList
. It may have been the intent to do this in the constructor:As before, this is incorrect:
For more information, see
List(Of T)
Class.Data Provider Objects
Working with databases presents many opportunities for a NullReference because there can be many objects (
Command
, Connection
, Transaction
, Dataset
, DataTable
, DataRows
..) in use at once. Note: It does not matter which data provider you are using -- MySQL, SQL Server, OleDB, etc. -- the concepts are the same.Example 1
As before, the
ds
Dataset object was declared, but an instance was never created. The DataAdapter
will fill an existing DataSet
, not create one. In this case, since ds
is a local variable, the IDE warns you that this might happen:When declared as a module/class level variable, as appears to be the case with
con
, the compiler can't know if the object was created by an upstream procedure. Do not ignore warnings.Remedy
Example 2
A typo is a problem here:
Employees
vs Employee
. There was no DataTable
named 'Employee' created, so a NullReferenceException
results trying to access it. Another potential problem is assuming there will be Items
which may not be so when the SQL includes a WHERE clause.Remedy
Since this uses one table, using
Tables(0)
will avoid spelling errors. Examining Rows.Count
can also help:Fill
is a function returning the number of Rows
affected which can also be tested:Example 3
The
DataAdapter
will provide TableNames
as shown in the previous example, but it does not parse names from the SQL or database table. As a result, ds.Tables('TICKET_RESERVATION')
references a non-existent table.The Remedy is the same, reference the table by index:
See also DataTable Class.
Object Paths / Nested
The code is only testing
Items
while both myFoo
and Bar
may also be Nothing. The remedy is to test the entire chain or path of objects one at a time:AndAlso
is important. Subsequent tests will not be performed once the first False
condition is encountered. This allows the code to safely 'drill' into the object(s) one 'level' at a time, evaluating myFoo.Bar
only after (and if) myFoo
is determined to be valid. Object chains or paths can get quite long when coding complex objects:It is not possible to reference anything 'downstream' of a
null
object. This also applies to controls:Here,
myWebBrowser
or Document
could be Nothing or the formfld1
element may not exist.UI Controls
Among other things, this code does not anticipate that the user may not have selected something in one or more UI controls.
ListBox1.SelectedItem
may well be Nothing
, so ListBox1.SelectedItem.ToString
will result in an NRE.Remedy
Validate data before using it (also use
Option Strict
and SQL parameters):Alternatively, you can use
(ComboBox5.SelectedItem IsNot Nothing) AndAlso..
Visual Basic Forms
This is a fairly common way to get an NRE. In C#, depending on how it is coded, the IDE will report that
Controls
does not exist in the current context, or 'cannot reference non-static member'. So, to some extent, this is a VB-only situation. It is also complex because it can result in a failure cascade.The arrays and collections cannot be initialized this way. This initialization code will run before the constructor creates the
Form
or the Controls
. As a result:- Lists and Collection will simply be empty
- The Array will contain five elements of Nothing
- The
somevar
assignment will result in an immediate NRE because Nothing doesn't have a.Text
property
Referencing array elements later will result in an NRE. If you do this in
Form_Load
, due to an odd bug, the IDE may not report the exception when it happens. The exception will pop up later when your code tries to use the array. This 'silent exception' is detailed in this post. For our purposes, the key is that when something catastrophic happens while creating a form (Sub New
or Form Load
event), exceptions may go unreported, the code exits the procedure and just displays the form.Since no other code in your
Sub New
or Form Load
event will run after the NRE, a great many other things can be left uninitialized.Note this applies to any and all control and component references making these illegal where they are:
Partial Remedy
Stop skype from opening on startup. It is curious that VB does not provide a warning, but the remedy is to declare the containers at the form level, but initialize them in form load event handler when the controls do exist. This can be done in
Sub New
as long as your code is after the InitializeComponent
call:The array code may not be out of the woods yet. Any controls which are in a container control (like a
GroupBox
or Panel
) will not be found in Me.Controls
; they will be in the Controls collection of that Panel or GroupBox. Nor will a control be returned when the control name is misspelled ('TeStBox2'
). In such cases, Nothing
will again be stored in those array elements and an NRE will result when you attempt to reference it.These should be easy to find now that you know what you are looking for:
'Button2' resides on a
Panel
Remedy
Rather than indirect references by name using the form's
Controls
collection, use the control reference:Function Returning Nothing
This is a case where the IDE will warn you that 'not all paths return a value and a
NullReferenceException
may result'. You can suppress the warning, by replacing Exit Function
with Return Nothing
, but that does not solve the problem. Anything which tries to use the return when someCondition = False
will result in an NRE:Remedy
Replace
Exit Function
in the function with Return bList
. Returning an emptyList
is not the same as returning Nothing
. If there is a chance that a returned object can be Nothing
, test before using it:Poorly Implemented Try/Catch
A badly implemented Try/Catch can hide where the problem is and result in new ones:
This is a case of an object not being created as expected, but also demonstrates the counter usefulness of an empty
Catch
.There is an extra comma in the SQL (after 'mailaddress') which results in an exception at
.ExecuteReader
. After the Catch
does nothing, Finally
tries to perform clean up, but since you cannot Close
a null DataReader
object, a brand new NullReferenceException
results.An empty
Catch
block is the devil's playground. This OP was baffled why he was getting an NRE in the Finally
block. In other situations, an empty Catch
may result in something else much further downstream going haywire and cause you to spend time looking at the wrong things in the wrong place for the problem. (The 'silent exception' described above provides the same entertainment value.)Remedy
Don't use empty Try/Catch blocks - let the code crash so you can a) identify the cause b) identify the location and c) apply a proper remedy. Try/Catch blocks are not intended to hide exceptions from the person uniquely qualified to fix them - the developer.
DBNull is not the same as Nothing
The
IsDBNull
function is used to test if a value equals System.DBNull
: From MSDN:The System.DBNull value indicates that the Object represents missing or non-existent data. DBNull is not the same as Nothing, which indicates that a variable has not yet been initialized.
Remedy
As before, you can test for Nothing, then for a specific value:
Example 2
FirstOrDefault
returns the first item or the default value, which is Nothing
for reference types and never DBNull
:Controls
If a
CheckBox
with chkName
can't be found (or exists in a GroupBox
), then chk
will be Nothing and be attempting to reference any property will result in an exception.Remedy
The DataGridView
The DGV has a few quirks seen periodically:
If
dgvBooks
has AutoGenerateColumns = True
, it will create the columns, but it does not name them, so the above code fails when it references them by name.Remedy
Name the columns manually, or reference by index:
Example 2 — Beware of the NewRow
When your
DataGridView
has AllowUserToAddRows
as True
(the default), the Cells
in the blank/new row at the bottom will all contain Nothing
. Most attempts to use the contents (for example, ToString
) will result in an NRE.Remedy
Use a
For/Each
loop and test the IsNewRow
property to determine if it is that last row. This works whether AllowUserToAddRows
is true or not:If you do use a
For n
loop, modify the row count or use Exit For
when IsNewRow
is true.My.Settings (StringCollection)
Under certain circumstances, trying to use an item from
My.Settings
which is a StringCollection
can result in a NullReference the first time you use it. The solution is the same, but not as obvious. Consider:Since VB is managing Settings for you, it is reasonable to expect it to initialize the collection. It will, but only if you have previously added an initial entry to the collection (in the Settings editor). Since the collection is (apparently) initialized when an item is added, it remains
Nothing
when there are no items in the Settings editor to add.Remedy
Initialize the settings collection in the form's
Load
event handler, if/when needed:Typically, the
Settings
collection will only need to be initialized the first time the application runs. An alternate remedy is to add an initial value to your collection in Project -> Settings | FooBars, save the project, then remove the fake value.You probably forgot the
New
operator.or
Something you assumed would perform flawlessly to return an initialized object to your code, did not.
![String reference not set to an instance String reference not set to an instance](/uploads/1/2/3/9/123947688/819092428.png)
Don't ignore compiler warnings (ever) and use
Option Strict On
(always).Another scenario is when you cast a null object into a value type. For example, the code below:
It will throw a
NullReferenceException
on the cast. It seems quite obvious in the above sample, but this can happen in more 'late-binding' intricate scenarios where the null object has been returned from some code you don't own, and the cast is for example generated by some automatic system.One example of this is this simple ASP.NET binding fragment with the Calendar control:
Here,
SelectedDate
is in fact a property - of DateTime
type - of the Calendar
Web Control type, and the binding could perfectly return something null. The implicit ASP.NET Generator will create a piece of code that will be equivalent to the cast code above. And this will raise a NullReferenceException
that is quite difficult to spot, because it lies in ASP.NET generated code which compiles fine..It means that the variable in question is pointed at nothing. I could generate this like so:
That will throw the error because while I've declared the variable '
connection
', it's not pointed to anything. When I try to call the member 'Open
', there's no reference for it to resolve, and it will throw the error.To avoid this error:
- Always initialize your objects before you try to do anything with them.
- If you're not sure whether the object is null, check it with
object null
.
JetBrains' Resharper tool will identify every place in your code that has the possibility of a null reference error, allowing you to put in a null check. This error is the number one source of bugs, IMHO.
It means your code used an object reference variable that was set to null (i.e. it did not reference an actual object instance).
To prevent the error, objects that could be null should be tested for null before being used.
Be aware that regardless of the scenario, the cause is always the same in .NET:
You are trying to use a reference variable whose value is
Nothing
/null
. When the value is Nothing
/null
for the reference variable, that means it is not actually holding a reference to an instance of any object that exists on the heap. You either never assigned something to the variable, never created an instance of the value assigned to the variable, or you set the variable equal to
Nothing
/null
manually, or you called a function that set the variable to Nothing
/null
for you.An example of this exception being thrown is: When you are trying to check something, that is null.
For example:
The .NET runtime will throw a NullReferenceException when you attempt to perform an action on something which hasn't been instantiated i.e. the code above.
In comparison to an ArgumentNullException which is typically thrown as a defensive measure if a method expects that what is being passed to it is not null.
More information is in C# NullReferenceException and Null Parameter.
If you have not initialized a reference type, and you want to set or read one of its properties, it will throw a NullReferenceException.
Example:
You can simply avoid this by checking if the variable is not null:
To fully understand why a NullReferenceException is thrown, it is important to know the difference between value types and reference types.
So, if you're dealing with value types, NullReferenceExceptions can not occur. Though you need to keep alert when dealing with reference types!
Only reference types, as the name is suggesting, can hold references or point literally to nothing (or 'null'). Whereas value types always contain a value.
Reference types (these ones must be checked):
- dynamic
- object
- string
Value types (you can simply ignore these ones):
- Numeric types
- Integral types
- Floating-point types
- decimal
- bool
- User defined structs
Another case where
NullReferenceExceptions
can happen is the (incorrect) use of the as
operator:Here,
Book
and Car
are incompatible types; a Car
cannot be converted/cast to a Book
. When this cast fails, as
returns null
. Using mybook
after this causes a NullReferenceException
.In general, you should use a cast or
as
, as follows:If you are expecting the type conversion to always succeed (ie. you know what the object should be ahead of time), then you should use a cast:
If you are unsure of the type, but you want to try to use it as a specific type, then use
as
:You are using the object that contains the null value reference. So it's giving a null exception. In the example the string value is null and when checking its length, the exception occurred.
Example:
The exception error is:
Unhandled Exception:
System.NullReferenceException: Object reference not set to an instance of an object. at Program.Main()
While what causes a NullReferenceExceptions and approaches to avoid/fix such an exception have been addressed in other answers, what many programmers haven't learned yet is how to independently debug such exceptions during development.
In Visual Studio this is usually easy thanks to the Visual Studio Debugger.
First, make sure that the correct error is going to be caught - seeHow do I allow breaking on 'System.NullReferenceException' in VS2010?Note1
Then either Start with Debugging (F5) or Attach [the VS Debugger] to Running Process. On occasion it may be useful to use
Debugger.Break
, which will prompt to launch the debugger.Now, when the NullReferenceException is thrown (or unhandled) the debugger will stop (remember the rule set above?) on the line on which the exception occurred. Sometimes the error will be easy to spot.
For instance,in the following line the only code that can cause the exception is if
myString
evaluates to null. This can be verified by looking at the Watch Window or running expressions in the Immediate Window.In more advanced cases, such as the following, you'll need to use one of the techniques above (Watch or Immediate Windows) to inspect the expressions to determine if
str1
was null or if str2
was null.Once where the exception is throw has been located, it's usually trivial to reason backwards to find out where the null value was [incorrectly] introduced --
Take the time required to understand the cause of the exception. Inspect for null expressions. Inspect the previous expressions which could have resulted in such null expressions. Add breakpoints and step through the program as appropriate. Use the debugger.
1 If Break on Throws is too aggressive and the debugger stops on an NPE in the .NET or 3rd-party library, Break on User-Unhandled can be used to limit the exceptions caught. Additionally, VS2012 introduces Just My Code which I recommend enabling as well.
If you are debugging with Just My Code enabled, the behavior is slightly different. With Just My Code enabled, the debugger ignores first-chance common language runtime (CLR) exceptions that are thrown outside of My Code and do not pass through My Code
Simon Mourier gave this example:
where an unboxing conversion (cast) from
object
(or from one of the classes System.ValueType
or System.Enum
, or from an interface type) to a value type (other than Nullable<>
) in itself gives the NullReferenceException
.In the other direction, a boxing conversion from a
Nullable<>
which has HasValue
equal to false
to a reference type, can give a null
reference which can then later lead to a NullReferenceException
. The classic example is:Sometimes the boxing happens in another way. For example with this non-generic extension method:
the following code will be problematic:
These cases arise because of the special rules the runtime uses when boxing
Nullable<>
instances.Adding a case when the class name for entity used in entity framework is same as class name for a web form code-behind file.
Suppose you have a web form Contact.aspx whose codebehind class is Contact and you have an entity name Contact.
Then following code will throw a NullReferenceException when you call context.SaveChanges()
For the sake of completeness DataContext class
and Contact entity class. Sometimes entity classes are partial classes so that you can extend them in other files too.
The error occurs when both the entity and codebehind class are in same namespace.To fix this, rename the entity class or the codebehind class for Contact.aspx.
ReasonI am still not sure about the reason. But whenever any of the entity class will extend System.Web.UI.Page this error occurs.
For discussion have a look at NullReferenceException in DbContext.saveChanges()
Another general case where one might receive this exception involves mocking classes during unit testing. Regardless of the mocking framework being used, you must ensure that all appropriate levels of the class hierarchy are properly mocked. In particular, all properties of
HttpContext
which are referenced by the code under test must be mocked.See 'NullReferenceException thrown when testing custom AuthorizationAttribute' for a somewhat verbose example.
I have a different perspective to answering this. This sort of answers 'what else can I do to avoid it?'
When working across different layers, for example in an MVC application, a controller needs services to call business operations. In such scenarios Dependency Injection Container can be used to initialize the services to avoid the NullReferenceException. So that means you don't need to worry about checking for null and just call the services from the controller as though they will always to available (and initialized) as either a singleton or a prototype.
On the matter of 'what should I do about it', there can be many answers.
A more 'formal' way of preventing such error conditions while developing is applying design by contract in your code. This means you need to set class invariants, and/or even function/method preconditions and postconditions on your system, while developing.
In short, class invariants ensure that there will be some constraints in your class that will not get violated in normal use (and therefore, the class will not get in an inconsistent state). Preconditions mean that data given as input to a function/method must follow some constraints set and never violate them, and postconditions mean that a function/method output must follow the set constraints again without ever violating them.Contract conditions should never be violated during execution of a bug-free program, therefore design by contract is checked in practice in debug mode, while being disabled in releases, to maximize the developed system performance.
This way, you can avoid
NullReferenceException
cases that are results of violation of the constraints set. For example, if you use an object property X
in a class and later try to invoke one of its methods and X
has a null value, then this will lead to NullReferenceException
:But if you set 'property X must never have a null value' as method precondition, then you can prevent the scenario described before:
For this cause, Code Contracts project exists for .NET applications.
Alternatively, design by contract can be applied using assertions.
UPDATE: It is worth mentioning that the term was coined by Bertrand Meyer in connection with his design of the Eiffel programming language.
A
NullReferenceException
is thrown when we are trying to access Properties of a null object or when a string value becomes empty and we are trying to access string methods.For example:
- When a string method of an empty string accessed:
- When a property of a null object accessed:
TL;DR: Try using
Html.Partial
instead of Renderpage
I was getting
Object reference not set to an instance of an object
when I tried to render a View within a View by sending it a Model, like this:Debugging showed the model was Null inside MyOtherView. Until I changed it to:
And it worked.
Furthermore, the reason I didn't have
Html.Partial
to begin with was because Visual Studio sometimes throws error-looking squiggly lines under Html.Partial
if it's inside a differently constructed foreach
loop, even though it's not really an error:But I was able to run the application with no problems with this 'error'. I was able to get rid of the error by changing the structure of the
foreach
loop to look like this:Although I have a feeling it was because Visual Studio was misreading the ampersands and brackets.
What can you do about it?
There is a lot of good answers here explaining what a null reference is and how to debug it. But there is very little on how to prevent the issue or at least make it easier to catch.
Check arguments
For example, methods can check the different arguments to see if they are null and throw an
ArgumentNullException
, an exception obviously created for this exact purpose. The constructor for the
ArgumentNullException
even takes the name of the parameter and a message as arguments so you can tell the developer exactly what the problem is.Use Tools
There are also several libraries that can help. 'Resharper' for example can provide you with warnings while you are writing code, especially if you use their attribute: NotNullAttribute
There's 'Microsoft Code Contracts' where you use syntax like
Contract.Requires(obj != null)
which gives you runtime and compile checking: Introducing Code Contracts.There's also 'PostSharp' which will allow you to just use attributes like this:
By doing that and making PostSharp part of your build process
obj
will be checked for null at runtime. See: PostSharp null checkPlain Code Solution
Or you can always code your own approach using plain old code. For example here is a struct that you can use to catch null references. It's modeled after the same concept as
Nullable<T>
:You would use very similar to the same way you would use
Nullable<T>
, except with the goal of accomplishing exactly the opposite - to not allow null
. Here are some examples:NotNull<T>
is implicitly cast to and from T
so you can use it just about anywhere you need it. For example, you can pass a Person
object to a method that takes a NotNull<Person>
:As you can see above as with nullable you would access the underlying value through the
Value
property. Alternatively, you can use an explicit or implicit cast, you can see an example with the return value below:Or you can even use it when the method just returns
T
(in this case Person
) by doing a cast. For example, the following code would just like the code above:Combine with Extension
Combine
NotNull<T>
with an extension method and you can cover even more situations. Here is an example of what the extension method can look like:And here is an example of how it could be used:
GitHub
For your reference I made the code above available on GitHub, you can find it at:
Related Language Feature
C# 6.0 introduced the 'null-conditional operator' that helps with this a little. With this feature, you can reference nested objects and if any one of them is
null
the whole expression returns null
.This reduces the number of null checks you have to do in some cases. The syntax is to put a question mark before each dot. Take the following code for example:
Imagine that
country
is an object of type Country
that has a property called State
and so on. If country
, State
, County
, or City
is null
then address will be
null. Therefore you only have to check whether
addressis
null`.It's a great feature, but it gives you less information. It doesn't make it obvious which of the 4 is null.
Built-in like Nullable?
C# has a nice shorthand for
Nullable<T>
, you can make something nullable by putting a question mark after the type like so int?
. It would be nice if C# had something like the
NotNull<T>
struct above and had a similar shorthand, maybe the exclamation point (!) so that you could write something like: public void WriteName(Person! person)
.You can fix NullReferenceException in a clean way using Null-conditional Operators in c#6 and write less code to handle null checks.
It's used to test for null before performing a member access (?.) or index (?[) operation.
Example
is equivalent to:
The result is that the name will be null when p is null or when p.Spouse is null.
Otherwise, the variable name will be assigned the value of the p.Spouse.FirstName.
For More details : Null-conditional Operators
The error line 'Object reference not set to an instance of an object.' states that you have not assigned instance object to a object reference and still you are accessing properies/methods of that object.
for example: let say you have a class called myClass and it contains one property prop1.
Now you are accessing this prop1 in some other class just like below:
above line throws error because reference of class myClass is declared but not instantiated or an instance of object is not assigned to referecne of that class.
To fix this you have to instantiate (assign object to reference of that class).
Interestingly, none of the answers on this page mention the two edge cases, hope no one minds if I add them:
Edge case #1: concurrent access to a Dictionary
Generic dictionaries in .NET are not thread-safe and they sometimes might throw a
NullReference
or even (more frequent) a KeyNotFoundException
when you try to access a key from two concurrent threads. The exception is quite misleading in this case.Edge case #2: unsafe code
If a
NullReferenceException
is thrown by unsafe
code, you might look at your pointer variables, and check them for IntPtr.Zero
or something. Which is the same thing ('null pointer exception'), but in unsafe code, variables are often cast to value-types/arrays, etc., and you bang your head against the wall, wondering how a value-type can throw this exception. (Another reason for non-using unsafe code unless you need it, by the way)
NullReferenceException or Object reference not set to an instance of an object occurs when an object of the class you are trying to use is not instantiated.For example:
Assume that you have a class named Student.
Now, consider another class where you are trying to retrieve the student's full name.
As seen in the above code, the statement Student s - only declares the variable of type Student, note that the Student class is not instantiated at this point.Hence, when the statement s.GetFullName() gets executed, it will throw the NullReferenceException.
Well, in simple terms:
You are trying to access an object that isn't created or currently not in memory.
So how to tackle this:
- Debug and let the debugger break.. It will directly take you to the variable that is broken.. Now your task is to simply fix this. Using the new keyword in the appropriate place.
- If it is caused on some database commands because the object isn't present then all you need to do is do a null check and handle it:
- The hardest one . if the GC collected the object already.. This generally occurs if you are trying to find an object using strings.. That is, finding it by name of the object then it may happen that the GC might already cleaned it up.. This is hard to find and will become quite a problem.. A better way to tackle this is do null checks wherever necessary during the development process. This will save you a lot of time.
By finding by name I mean some framework allow you to FIndObjects using strings and the code might look like this: FindObject('ObjectName');
If we consider common scenarios where this exception can be thrown, accessing properties withing object at the top.
Ex:
in here , if address is null , then you will get NullReferenceException.
So, as a practice we should always use null check, before accessing properties in such objects (specially in generic)
Literally the easiest way to fix a NullReferenceExeption has two ways.If you have a GameObject for example with a script attached and a variable named rb (rigidbody) this variable will start null when you start your game.
This is why you get a NullReferenceExeption because the computer does not have data stored in that variable.
This is why you get a NullReferenceExeption because the computer does not have data stored in that variable.
I'll be using a RigidBody variable as an example.
We can add data really easily actually in a few ways:
We can add data really easily actually in a few ways:
- Add a RigidBody to your object with AddComponent > Physics > Rigidbody
Then go into your script and typerb = GetComponent<Rigidbody>();
This line of code works best under yourStart()
orAwake()
functions. - You can add a component programmatically and assign the variable at the same time with one line of code:
rb = AddComponent<RigidBody>();
Further Notes: If you want unity to add a component to your object and you might have forgotten to add one, you can type
Enjoy and have fun making games!
[RequireComponent(typeof(RigidBody))]
above your class declaration (the space below all of your usings).Enjoy and have fun making games!
If one is getting this message during saving or compiling the build, just close all the files and then open any file to compile and save.
For me the reason was that I had rename the file and old file was still open.
To use methods and member of an object you first have to create that object. If you didn't create it (variable that should hold the object is not initialized), but you try to use it's methods or variables you'll get that error.
Sometime you may just forgot to do initialization.
Edited: new can't return null, but fire's exception when failed. Long time ago it was the case in some languages, but not any more. Thanks @John Saunders for pointing that out.
This is basically is a Null reference exception. As Microsoft states-
A NullReferenceException exception is thrown when you try to access a member of a type whose value is null.
What does that mean?
That means if any member which doesn’t hold any value and we are making that member to perform certain task then the system will undoubtedly toss a message and say-
“Hey wait, that member has no values so it can’t perform the task which you are handing it over.”
The exception itself says that something is being referred but whose value is not being set. So this denotes that it only occurs while using reference types as Value types are non-nullable.
NullReferenceException won't occur if we are using Value type members.
The above code shows simple string which is assigned with a null value.
Now, when I try to print the length of the string str, I do get An unhandled exception of type ‘System.NullReferenceException’ occurred message because member str is pointing to null and there can’t be any length of null.
‘NullReferenceException’ also occurs when we forget to instantiate a reference type.
Suppose I have a class and member method in it. I have not instantiated my class but only named my class. Now if I try to use the method, the compiler will throw an error or issue a warning (depending on the compiler).
Compiler for the above code raises an error that variable obj is unassigned which signifies that our variable has null values or nothing. Compiler for the above code raises an error that variable obj is unassigned which signifies that our variable has null values or nothing.
Why it occurs?
- NullReferenceException arises due to our fault for not checking the object’s value. We often leave the object values unchecked in the code development.
- It also arises when we forget to instantiate our objects. Using methods, properties, collections etc. which can return or set null values can also be the cause of this exception.
How can it be avoided?
There are various ways and methods to avoid this renowned exception:
- Explicit Checking: We should adhere to the tradition of checking the objects, properties, methods, arrays, and collections whether they are null. This can be simply implemented using conditional statements like if-else if-else etc.
- Exception handling: One of the important ways of managing this exception. Using simple try-catch-finally blocks we can control this exception and also maintain a log of it. This can be very useful when your application is on production stage.
- Null operators: Null Coalescing operator and null conditional operators can also be used in handy while setting values to objects, variables, properties and fields.
- Debugger: For developers, we have the big weapon of Debugging with us. If have we face NullReferenceException during the development face we can use the debugger to get to the source of the exception.
- In-built method: System methods such as GetValueOrDefault(),IsNullOrWhiteSpace() and IsNullorEmpty() checks for nulls and assign the default value if there is a null value.
There are many good answers already here. You can also check more detailed description with examples on my blog.
Hope this helps too!
There is a scenario that can happen that is Class related. The question ended up getting closed prior to my stating the resolution:https://stackoverflow.com/questions/43348009/unable-to-instantiate-class
Beware of classes not instantiating: If any part of your constructor in a class throws a
null reference exception
the class does not instantiate. In my case it was trying to get a connection string from the web.config that that did not exist. I instantiated a class:
Inside the class itself was a call to get a connection string from the
web.config
. This part of the constructor threw an null value exception so myClass
was null.If you ever have a situation where a class in not instantiating, try making sure that no part of the class constructor Is throwing a
null value exception
. F-11 and step through the class and make sure there are no nulls.12 next
Not the answer you're looking for? Browse other questions tagged c#.netvb.netnullnullreferenceexception or ask your own question.
Please help me. Do you know why I'm receiving this message meanwhile I'm testing my game?.
NullReferenceException: Object reference not set to an instance of an object UnityEditor.ListViewShared.HasMouseDown (UnityEditor.InternalListViewState ilvState, Rect r, Int32 button) (at C:/BuildAgent/work/6bc5f79e0a4296d6/Editor/Mono/GUI/ListViewShared.cs:180) UnityEditor.ListViewShared.HasMouseDown (UnityEditor.InternalListViewState ilvState, Rect r) (at C:/BuildAgent/work/6bc5f79e0a4296d6/Editor/Mono/GUI/ListViewShared.cs:175) UnityEditor.ListViewShared+ListViewElementsEnumerator.MoveNext () (at C:/BuildAgent/work/6bc5f79e0a4296d6/Editor/Mono/GUI/ListViewShared.cs:368) UnityEditor.ConsoleWindow.OnGUI () (at C:/BuildAgent/work/6bc5f79e0a4296d6/Editor/Mono/ConsoleWindow.cs:422) System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture)
Thank you very much.
This question already has an answer here:
- What is a NullReferenceException, and how do I fix it? 31 answers
- What does “Object reference not set to an instance of an object” mean? [duplicate] 8 answers
Nullreferenceexception Object Reference Not Set To An Instance Of An Object
I keep getting this error when I run the program.
Object reference not set to an instance of an object. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.
What is the correct way it should be written?
Malachi2,68144 gold badges2424 silver badges4242 bronze badges
MikeMike1,1051111 gold badges3434 silver badges5252 bronze badges
marked as duplicate by Roman C, Daniel Kelley, Johann Blais, C-Pound Guru, Dour High ArchJul 18 '14 at 16:32
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
5 Answers
The correct way in .NET 4.0 is:
The
String.IsNullOrWhiteSpace
method used above is equivalent to:Reference for IsNullOrWhiteSpace method
Indicates whether a specified string is Nothing, empty, or consists only of white-space characters.
In earlier versions, you could do something like this:
The
String.IsNullOrEmpty
method used above is equivalent to:Which means you still need to check for your 'IsWhiteSpace' case with the
.Trim().Length 0
as per the example.Reference for IsNullOrEmpty method
Indicates whether the specified string is Nothing or an Empty string.
Explanation:
You need to ensure
strSearch
(or any variable for that matter) is not null
before you dereference it using the dot character (.
) - i.e. before you do strSearch.SomeMethod()
or strSearch.SomeProperty
you need to check that strSearch != null
.In your example you want to make sure your string has a value, which means you want to ensure the string:
- Is not null
- Is not the empty string (
String.Empty
/'
) - Is not just whitespace
In the cases above, you must put the 'Is it null?' case first, so it doesn't go on to check the other cases (and error) when the string is
Matt MitchellMatt Mitchellnull
.24.9k3333 gold badges104104 silver badges173173 bronze badges
kevinji8,80544 gold badges2929 silver badges5252 bronze badges
Ritch MeltonRitch Melton10.4k44 gold badges3131 silver badges5151 bronze badges
strSearch in this case is probably null (not simply empty).
Try using
String.IsNullOrEmpty(strSearch)
if you are just trying to determine if the string doesn't have any contents.
Cameron HotchkiesCameron Hotchkies1,10211 gold badge1010 silver badges1818 bronze badges
I know this was posted about a year ago, but this is for users for future reference.
I came across similar issue. In my case (i will try to be brief, please do let me know if you would like more detail), i was trying to check if a string was empty or not (string is the subject of an email). It always returned the same error message no matter what i did. I knew i was doing it right but it still kept throwing the same error message. Then it dawned in me that, i was checking if the subject (string) of an email (instance/object), what if the email(instance) was already a null at the first place. How could i check for a subject of an email, if the email is already a null.i checked if the the email was empty, it worked fine.
while checking for the subject(string) i used IsNullorWhiteSpace(), IsNullOrEmpty() methods.
Kevin Gosse34.2k33 gold badges5656 silver badges7474 bronze badges
MaraduarzMaraduarz
I want to extend MattMitchell's answer by saying you can create an extension method for this functionality:
This makes it possible to call:
Nullreferenceexception Object Reference Not Set To An Instance Of An Object Rust
To me this is a lot cleaner than calling the static
MrSnowflakeMrSnowflakeString
function, while still being NullReference safe!3,85122 gold badges2525 silver badges3232 bronze badges