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NullReferenceException Class

The exception that is thrown when there is an attempt to dereference a null object reference.

System.Object
  System.Exception
    System.SystemException
      System.NullReferenceException

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

'Declaration
<SerializableAttribute> _
<ComVisibleAttribute(True)> _
Public Class NullReferenceException _
	Inherits SystemException

The NullReferenceException type exposes the following members.

  NameDescription
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsNullReferenceExceptionInitializes a new instance of the NullReferenceException class, setting the Message property of the new instance to a system-supplied message that describes the error, such as "The value 'null' was found where an instance of an object was required." This message takes into account the current system culture.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsNullReferenceException(String)Initializes a new instance of the NullReferenceException class with a specified error message.
Protected methodNullReferenceException(SerializationInfo, StreamingContext)Initializes a new instance of the NullReferenceException class with serialized data.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsNullReferenceException(String, Exception)Initializes a new instance of the NullReferenceException class with a specified error message and a reference to the inner exception that is the cause of this exception.
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  NameDescription
Public propertySupported by Portable Class LibrarySupported in .NET for Windows Store appsDataGets a collection of key/value pairs that provide additional user-defined information about the exception. (Inherited from Exception.)
Public propertySupported by Portable Class LibrarySupported in .NET for Windows Store appsHelpLinkGets or sets a link to the help file associated with this exception. (Inherited from Exception.)
Public propertySupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsHResultGets or sets HRESULT, a coded numerical value that is assigned to a specific exception. (Inherited from Exception.)
Public propertySupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsInnerExceptionGets the Exception instance that caused the current exception. (Inherited from Exception.)
Public propertySupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsMessageGets a message that describes the current exception. (Inherited from Exception.)
Public propertySupported by Portable Class LibrarySupported in .NET for Windows Store appsSourceGets or sets the name of the application or the object that causes the error. (Inherited from Exception.)
Public propertySupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsStackTraceGets a string representation of the immediate frames on the call stack. (Inherited from Exception.)
Public propertyTargetSiteGets the method that throws the current exception. (Inherited from Exception.)
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  NameDescription
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsEquals(Object)Determines whether the specified object is equal to the current object. (Inherited from Object.)
Protected methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsGetBaseExceptionWhen overridden in a derived class, returns the Exception that is the root cause of one or more subsequent exceptions. (Inherited from Exception.)
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsGetHashCodeServes as the default hash function. (Inherited from Object.)
Public methodGetObjectDataWhen overridden in a derived class, sets the SerializationInfo with information about the exception. (Inherited from Exception.)
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsGetTypeGets the runtime type of the current instance. (Inherited from Exception.)

In XNA Framework 3.0, this member is inherited from Object.GetType.


In Portable Class Library Portable Class Library, this member is inherited from Object.GetType.


In .NET for Windows Store apps Windows 8, this member is inherited from Object.GetType.
Protected methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsToStringCreates and returns a string representation of the current exception. (Inherited from Exception.)
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  NameDescription
Protected eventSerializeObjectStateOccurs when an exception is serialized to create an exception state object that contains serialized data about the exception. (Inherited from Exception.)
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A NullReferenceException exception is thrown when you try to access a member on a type whose value is Nothing. The following example illustrates one such scenario:

Imports System.Collections.Generic

Module Example
   Public Sub Main()
      Dim names As List(Of String)
      names.Add("Major Major Major")       
   End Sub 
End Module 
' Compilation displays a warning like the following: 
'    Example1.vb(10) : warning BC42104: Variable 'names' is used before it  
'    has been assigned a value. A null reference exception could result  
'    at runtime. 
'     
'          names.Add("Major Major Major") 
'          ~~~~~ 
' The example displays output like the following output: 
'    Unhandled Exception: System.NullReferenceException: Object reference  
'    not set to an instance of an object. 
'       at Example.Main()

Some compilers issue a warning when they compile this code. Others issue an error, and the compilation fails. To address this problem, instantiate the object so that its value is no longer Nothing. The following example does this by calling a type's class constructor.

Imports System.Collections.Generic

Module Example
   Public Sub Main()
      Dim names As New List(Of String)()
      names.Add("Major Major Major")       
   End Sub 
End Module

More commonly, a NullReferenceException exception is thrown by a method that is passed Nothing. Some methods validate the arguments that are passed to them. If they do and one of the arguments is Nothing, the method throws an System.ArgumentNullException exception. Otherwise, it throws a NullReferenceException exception. The following example illustrates this scenario.

Imports System.Collections.Generic

Module Example
   Public Sub Main()
      Dim names As List(Of String) = GetData()
      PopulateNames(names)
   End Sub 

   Private Sub PopulateNames(names As List(Of String))
      Dim arrNames() As String = { "Dakota", "Samuel", "Nikita",
                                   "Koani", "Saya", "Yiska", "Yumaevsky" }
      For Each arrName In arrNames
         names.Add(arrName)
      Next 
   End Sub 

   Private Function GetData() As List(Of String)
      Return Nothing    
   End Function 
End Module 
' The example displays output like the following: 
'    Unhandled Exception: System.NullReferenceException: Object reference  
'    not set to an instance of an object. 
'       at Example.PopulateNames(List`1 names) 
'       at Example.Main()

To address this issue, make sure that the argument passed to the method is not Nothing, or handle the thrown exception in a try…catch…finally block. For more information, see Handling and Throwing Exceptions.

The following Microsoft intermediate language (MSIL) instructions throw NullReferenceException: callvirt, cpblk, cpobj, initblk, ldelem.<type>, ldelema, ldfld, ldflda, ldind.<type>, ldlen, stelem.<type>, stfld, stind.<type>, throw, and unbox.

NullReferenceException uses the HRESULT COR_E_NULLREFERENCE, which has the value 0x80004003.

For a list of initial property values for an instance of NullReferenceException, see the NullReferenceException constructors.

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
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