InvalidCastException Class

Definition

The exception that is thrown for invalid casting or explicit conversion.

[System.Runtime.InteropServices.ComVisible(true)]
public class InvalidCastException : SystemException
Inheritance
InvalidCastException
Attributes

Remarks

The .NET Framework supports automatic conversion from derived types to their base types and back to the derived type, as well as from types that present interfaces to interface objects and back. It also includes a variety of mechanisms that support custom conversions. For more information, see Type Conversion in the .NET Framework.

An InvalidCastException exception is thrown when the conversion of an instance of one type to another type is not supported. For example, attempting to convert a Char value to a DateTime value throws an InvalidCastException exception. It differs from an OverflowException exception, which is thrown when a conversion of one type to another is supported, but the value of the source type is outside the range of the target type. An InvalidCastException exception is caused by developer error and should not be handled in a try/catch block; instead, the cause of the exception should be eliminated.

For information about conversions supported by the system, see the Convert class. For errors that occur when the destination type can store source type values, but is not large enough to store a specific source value, see the OverflowException exception.

Note

In many cases, your language compiler detects that no conversion exists between the source type and the target type and issues a compiler error.

Some of the conditions under which an attempted conversion throws an InvalidCastException exception are discussed in the following sections:

Primitive types and IConvertible
The Convert.ChangeType method
Narrowing conversions and IConvertible implementations
Downcasting
Conversion from an interface object
String conversions
Visual Basic 6.0 migration

For an explicit reference conversion to be successful, the source value must be null, or the object type referenced by the source argument must be convertible to the destination type by an implicit reference conversion.

The following intermediate language (IL) instructions throw an InvalidCastException exception:

  • castclass

  • refanyval

  • unbox

InvalidCastException uses the HRESULT COR_E_INVALIDCAST, which has the value 0x80004002.

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

Primitive types and IConvertible

You directly or indirectly call a primitive type's IConvertible implementation that does not support a particular conversion. For example, trying to convert a Boolean value to a Char or a DateTime value to an Int32 throws an InvalidCastException exception. The following example calls both the Boolean.IConvertible.ToChar and Convert.ToChar(Boolean) methods to convert a Boolean value to a Char. In both cases, the method call throws an InvalidCastException exception.

using System;

public class Example
{
   public static void Main()
   {
      bool flag = true;
      try {
         IConvertible conv = flag;
         Char ch = conv.ToChar(null);
         Console.WriteLine("Conversion succeeded.");
      }   
      catch (InvalidCastException) {   
         Console.WriteLine("Cannot convert a Boolean to a Char.");
      }
      
      try {
         Char ch = Convert.ToChar(flag);
         Console.WriteLine("Conversion succeeded.");
      }   
      catch (InvalidCastException) {   
         Console.WriteLine("Cannot convert a Boolean to a Char.");
      }
   }
}
// The example displays the following output:
//       Cannot convert a Boolean to a Char.
//       Cannot convert a Boolean to a Char.
Module Example
   Public Sub Main()
      Dim flag As Boolean = True
      Try
         Dim conv As IConvertible = flag
         Dim ch As Char = conv.ToChar(Nothing)
         Console.WriteLine("Conversion succeeded.")
      Catch e As InvalidCastException   
         Console.WriteLine("Cannot convert a Boolean to a Char.")
      End Try
      
      Try
         Dim ch As Char = Convert.ToChar(flag)
         Console.WriteLine("Conversion succeeded.")
      Catch e As InvalidCastException   
         Console.WriteLine("Cannot convert a Boolean to a Char.")
      End Try
   End Sub
End Module
' The example displays the following output:
'       Cannot convert a Boolean to a Char.
'       Cannot convert a Boolean to a Char.

Because the conversion is not supported, there is no workaround.

The Convert.ChangeType method

You've called the Convert.ChangeType method to convert an object from one type to another, but one or both types don't implement the IConvertible interface.

In most cases, because the conversion is not supported, there is no workaround. In some cases, a possible workaround is to manually assign property values from the source type to similar properties of a the target type.

Narrowing conversions and IConvertible implementations

Narrowing operators define the explicit conversions supported by a type. A casting operator in C# or the CType conversion method in Visual Basic (if Option Strict is on) is required to perform the conversion.

However, if neither the source type nor the target type defines an explicit or narrowing conversion between the two types, and the IConvertible implementation of one or both types doesn't support a conversion from the source type to the target type, an InvalidCastException exception is thrown.

In most cases, because the conversion is not supported, there is no workaround.

Downcasting

You are downcasting, that is, trying to convert an instance of a base type to one of its derived types. In the following example, trying to convert a Person object to a PersonWithID object fails.

using System;

public class Person
{
   String _name;
   
   public String Name 
   { 
      get { return _name; }
      set { _name = value; }
   }
}

public class PersonWithId : Person
{
   String _id;
   
   public string Id
   {
      get { return _id; }
      set { _id = value; }
   }
}

public class Example
{
   public static void Main()
   {
      Person p = new Person();
      p.Name = "John";
      try {
         PersonWithId pid = (PersonWithId) p;
         Console.WriteLine("Conversion succeeded.");
      }   
      catch (InvalidCastException) {
         Console.WriteLine("Conversion failed.");
      } 
      
      PersonWithId pid1 = new PersonWithId();
      pid1.Name = "John";
      pid1.Id = "246";
      Person p1 = pid1;
      try {   
         PersonWithId pid1a = (PersonWithId) p1;
         Console.WriteLine("Conversion succeeded.");
      }   
      catch (InvalidCastException) {
         Console.WriteLine("Conversion failed.");
      } 
      
      Person p2 = null;
      try {   
         PersonWithId pid2 = (PersonWithId) p2;
         Console.WriteLine("Conversion succeeded.");
      }   
      catch (InvalidCastException) {
         Console.WriteLine("Conversion failed.");
      } 
   }
}
// The example displays the following output:
//       Conversion failed.
//       Conversion succeeded.
//       Conversion succeeded.
Public Class Person
   Dim _name As String
   
   Public Property Name As String
      Get
         Return _name
      End Get
      Set
         _name = value
      End Set
   End Property
End Class

Public Class PersonWithID : Inherits Person
   Dim _id As String
   
   Public Property Id As String
      Get
         Return _id
      End Get
      Set
         _id = value
      End Set
   End Property
End Class

Module Example
   Public Sub Main()
      Dim p As New Person()
      p.Name = "John"
      Try
         Dim pid As PersonWithId = CType(p, PersonWithId)
         Console.WriteLine("Conversion succeeded.")
      Catch e As InvalidCastException
         Console.WriteLine("Conversion failed.")
      End Try 
      
      Dim pid1 As New PersonWithId()
      pid1.Name = "John"
      pid1.Id = "246"
      Dim p1 As Person = pid1
      
      Try   
         Dim pid1a As PersonWithId = CType(p1, PersonWithId)
         Console.WriteLine("Conversion succeeded.")
      Catch e As InvalidCastException
         Console.WriteLine("Conversion failed.")
      End Try 
      
      Dim p2 As Person = Nothing
      Try   
         Dim pid2 As PersonWithId = CType(p2, PersonWithId)
         Console.WriteLine("Conversion succeeded.")
      Catch e As InvalidCastException
         Console.WriteLine("Conversion failed.")
      End Try 
   End Sub
End Module
' The example displays the following output:
'       Conversion failed.
'       Conversion succeeded.
'       Conversion succeeded.

As the example shows, the downcast succeeds only if the Person object was created by an upcast from a PersonWithId object to a Person object, or if the Person object is null.

Conversion from an interface object

You are attempting to convert an interface object to a type that implements that interface, but the target type is not the same type or a base class of the type from which the interface object was originally derived. The following example throws an InvalidCastException exception when it attempts to convert an IFormatProvider object to a DateTimeFormatInfo object. The conversion fails because although the DateTimeFormatInfo class implements the IFormatProvider interface, the DateTimeFormatInfo object is not related to the CultureInfo class from which the interface object was derived.

using System;
using System.Globalization;

public class Example
{
   public static void Main()
   {
      var culture = CultureInfo.InvariantCulture;
      IFormatProvider provider = culture;
      
      DateTimeFormatInfo dt = (DateTimeFormatInfo) provider;
   }
}
// The example displays the following output:
//    Unhandled Exception: System.InvalidCastException: 
//       Unable to cast object of type //System.Globalization.CultureInfo// to 
//           type //System.Globalization.DateTimeFormatInfo//.
//       at Example.Main()
Imports System.Globalization

Module Example
   Public Sub Main()
      Dim culture As CultureInfo = CultureInfo.InvariantCulture
      Dim provider As IFormatProvider = culture
      
      Dim dt As DateTimeFormatInfo = CType(provider, DateTimeFormatInfo)
   End Sub
End Module
' The example displays the following output:
'    Unhandled Exception: System.InvalidCastException: 
'       Unable to cast object of type 'System.Globalization.CultureInfo' to 
'           type 'System.Globalization.DateTimeFormatInfo'.
'       at Example.Main()

As the exception message indicates, the conversion would succeed only if the interface object is converted back to an instance of the original type, in this case a CultureInfo. The conversion would also succeed if the interface object is converted to an instance of a base type of the original type.

String conversions

You are trying to convert a value or an object to its string representation by using a casting operator in C#. In the following example, both the attempt to cast a Char value to a string and the attempt to cast an integer to a string throw an InvalidCastException exception.

using System;

public class Example
{
   public static void Main()
   {
      object value = 12;
      // Cast throws an InvalidCastException exception.
      string s = (string) value;
   }
}

Note

Using the Visual Basic CStr operator to convert a value of a primitive type to a string succeeds. The operation does not throw an InvalidCastException exception.

To successfully covert an instance of any type to its string representation, call its ToString method, as the following example does. The ToString method is always present, since the ToString method is defined by the Object class and therefore is either inherited or overridden by all managed types.

using System;

public class Example
{
   public static void Main()
   {
      object value = 12;
      string s = value.ToString();
      Console.WriteLine(s);
   }
}
// The example displays the following output:
//      12

Visual Basic 6.0 migration

You're upgrading a Visual Basic 6.0 application with a call to a custom event in a user control to Visual Basic .NET, and an InvalidCastException exception is thrown with the message, "Specified cast is not valid." To eliminate this exception, change the line of code in your form (such as Form1)

Call UserControl11_MyCustomEvent(UserControl11, New UserControl1.MyCustomEventEventArgs(5))  

and replace it with the following line of code:

Call UserControl11_MyCustomEvent(UserControl11(0), New UserControl1.MyCustomEventEventArgs(5))  

Constructors

InvalidCastException()

Initializes a new instance of the InvalidCastException class.

InvalidCastException(SerializationInfo, StreamingContext)

Initializes a new instance of the InvalidCastException class with serialized data.

InvalidCastException(String)

Initializes a new instance of the InvalidCastException class with a specified error message.

InvalidCastException(String, Exception)

Initializes a new instance of the InvalidCastException class with a specified error message and a reference to the inner exception that is the cause of this exception.

InvalidCastException(String, Int32)

Initializes a new instance of the InvalidCastException class with a specified message and error code.

Properties

Data Inherited from Exception
HResult Inherited from Exception
HelpLink Inherited from Exception
InnerException Inherited from Exception
Message Inherited from Exception
Source Inherited from Exception
StackTrace Inherited from Exception
TargetSite Inherited from Exception

Methods

Equals(Object) Inherited from Object
Equals(Object, Object) Inherited from Object
GetBaseException() Inherited from Exception
GetHashCode() Inherited from Object
GetObjectData(SerializationInfo, StreamingContext) Inherited from Exception
GetType() Inherited from Exception
MemberwiseClone() Inherited from Object
ReferenceEquals(Object, Object) Inherited from Object
ToString() Inherited from Exception

Events

SerializeObjectState Inherited from Exception

Applies to

See Also