Not​Supported​Exception Class

Definition

The exception that is thrown when an invoked method is not supported, or when there is an attempt to read, seek, or write to a stream that does not support the invoked functionality.

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

Inherited Members

Remarks

NotSupportedException indicates that no implementation exists for an invoked method or property.

NotSupportedException uses the HRESULT COR_E_NOTSUPPORTED, which has the value 0x80131515.

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

Throwing a NotSupportedException exception

You might consider throwing a NotSupportedException exception in the following cases:

  • You are implementing a general-purpose interface, and number of the methods have no meaningful implementation. For example, if you are creating a date and time type that implements the IConvertible interface, you would throw a NotSupportedException exception for most of the conversions.

  • You've inherited from an abstract class that requires that you override a number of methods. However, you're only prepared to provide an implementation for a subset of these. For the methods that you decide not to implement, you can choose to throw a NotSupportedException.

  • You are defining a general-purpose type with a state that enables operations conditionally. For example, your type can be either read-only or read-write. In that case:

    • If the object is read-only, attempting to assign values to the properties of an instance or call methods that modify instance state should throw a NotSupportedException exception.

    • You should implement a property that returns a Boolean value that indicates whether particular functionality is available. For example, for a type that can be either read-only or read-write, you could implement a IsReadOnly property that indicates whether the set of read-write methods are available or unavailable.

Handling a NotSupportedException exception

The NotSupportedException exception indicates that a method has no implementation and that you should not call it. You should not handle the exception. Instead, what you should do depends on the cause of the exception: whether an implementation is completely absent , or the member invocation is inconsistent with the purpose of an object (such as a call to the FileStream.Read method on a read-only FileStream object .

An implementation has not been provided because the operation cannot be performed in a meaningful way.
This is a common exception when you are calling methods on an object that provides implementations for the methods of an abstract base class, or that implements a general-purpose interface, and the method has no meaningful implementation.

For example, the Convert class implements the IConvertible interface, which means that it must include a method to convert every primitive type to every other primitive type. Many of those conversions, however, are not possible. As a result, a call to the Convert.ToBoolean(DateTime) method, for instance, throws a NotSupportedException exception because there is no possible conversion between a DateTime and a Boolean value

To eliminate the exception, you should eliminate the method call.

The method call is not supported given the state of the object.
You are attempting to invoke a member whose functionality is unavailable because of the object's state. You can eliminate the exception in one of three ways:

  • You know the state of the object in advance, but you've invoked an unsupported method or property. In this case, the member invocation is an error, and you can eliminate it.

  • You know the state of the object in advance (usually because your code has instantiated it), but the object is mis-configured. The following example illustrates this issue. It creates a read-only FileStream object and then attempts to write to it.

    using System;
    using System.IO;
    using System.Text;
    using System.Threading.Tasks;
    
    public class Example
    {
       public static void Main()
       {
          Encoding enc = Encoding.Unicode;
          String value = "This is a string to persist.";
          Byte[] bytes  = enc.GetBytes(value);
    
          FileStream fs = new FileStream(@".\TestFile.dat", 
                                         FileMode.Open,
                                         FileAccess.Read);
          Task t = fs.WriteAsync(enc.GetPreamble(), 0, enc.GetPreamble().Length);
          Task t2 = t.ContinueWith( (a) => fs.WriteAsync(bytes, 0, bytes.Length) ); 
          t2.Wait();
          fs.Close();
       }
    }
    // The example displays the following output:
    //    Unhandled Exception: System.NotSupportedException: Stream does not support writing.
    //       at System.IO.Stream.BeginWriteInternal(Byte[] buffer, Int32 offset, Int32 count, AsyncCallback callback, Object state
    //    , Boolean serializeAsynchronously)
    //       at System.IO.FileStream.BeginWrite(Byte[] array, Int32 offset, Int32 numBytes, AsyncCallback userCallback, Object sta
    //    teObject)
    //       at System.IO.Stream.<>c.<BeginEndWriteAsync>b__53_0(Stream stream, ReadWriteParameters args, AsyncCallback callback,
    //    Object state)
    //       at System.Threading.Tasks.TaskFactory`1.FromAsyncTrim[TInstance,TArgs](TInstance thisRef, TArgs args, Func`5 beginMet
    //    hod, Func`3 endMethod)
    //       at System.IO.Stream.BeginEndWriteAsync(Byte[] buffer, Int32 offset, Int32 count)
    //       at System.IO.FileStream.WriteAsync(Byte[] buffer, Int32 offset, Int32 count, CancellationToken cancellationToken)
    //       at System.IO.Stream.WriteAsync(Byte[] buffer, Int32 offset, Int32 count)
    //       at Example.Main()
    
    Imports System.IO
    Imports System.Text
    Imports System.Threading.Tasks
    
    Module Example
       Public Sub Main()
          Dim enc As Encoding = Encoding.Unicode
          Dim value As String = "This is a string to persist."
          Dim bytes() As Byte = enc.GetBytes(value)
    
          Dim fs As New FileStream(".\TestFile.dat", 
                                   FileMode.Open,
                                   FileAccess.Read)
          Dim t As Task = fs.WriteAsync(enc.GetPreamble(), 0, enc.GetPreamble().Length)
          Dim t2 As Task = t.ContinueWith(Sub(a) fs.WriteAsync(bytes, 0, bytes.Length)) 
          t2.Wait()
          fs.Close()
       End Sub
    End Module
    ' The example displays the following output:
    '    Unhandled Exception: System.NotSupportedException: Stream does not support writing.
    '       at System.IO.Stream.BeginWriteInternal(Byte[] buffer, Int32 offset, Int32 count, AsyncCallback callback, Object state
    '    , Boolean serializeAsynchronously)
    '       at System.IO.FileStream.BeginWrite(Byte[] array, Int32 offset, Int32 numBytes, AsyncCallback userCallback, Object sta
    '    teObject)
    '       at System.IO.Stream.<>c.<BeginEndWriteAsync>b__53_0(Stream stream, ReadWriteParameters args, AsyncCallback callback,
    '    Object state)
    '       at System.Threading.Tasks.TaskFactory`1.FromAsyncTrim[TInstance,TArgs](TInstance thisRef, TArgs args, Func`5 beginMet
    '    hod, Func`3 endMethod)
    '       at System.IO.Stream.BeginEndWriteAsync(Byte[] buffer, Int32 offset, Int32 count)
    '       at System.IO.FileStream.WriteAsync(Byte[] buffer, Int32 offset, Int32 count, CancellationToken cancellationToken)
    '       at System.IO.Stream.WriteAsync(Byte[] buffer, Int32 offset, Int32 count)
    '       at Example.Main()
    

    You can eliminate the exception by ensuring that the instantiated object supports the functionality you intend. The following example addresses the problem of the read-only FileStream object by providing the correct arguments to the FileStream.FileStream(String, FileMode, FileAccess) constructor.

  • You don't know the state of the object in advance, and the object doesn't support a particular operation. In most cases, the object should include a property or method that indicates whether it supports a particular set of operations. You can eliminate the exception by checking the value of the object and invoking the member only if appropriate.

    The following example defines a DetectEncoding method that throws a NotSupportedException exception when it attempts to read from the beginning of a stream that does not support read access.

    using System;
    using System.IO;
    using System.Threading.Tasks;
    
    public class Example
    {
       public static void Main()
       {
          String name = @".\TestFile.dat";
          var fs = new FileStream(name, 
                                  FileMode.Create,
                                  FileAccess.Write);
             Console.WriteLine("Filename: {0}, Encoding: {1}", 
                               name, FileUtilities.GetEncodingType(fs));
       }
    }
    
    public class FileUtilities
    {
       public enum EncodingType
       { None = 0, Unknown = -1, Utf8 = 1, Utf16 = 2, Utf32 = 3 }
       
       public static EncodingType GetEncodingType(FileStream fs)
       {
          Byte[] bytes = new Byte[4];
          var t = fs.ReadAsync(bytes, 0, 4);
          t.Wait();
          int bytesRead = t.Result;
          if (bytesRead < 2)
             return EncodingType.None;
          
          if (bytesRead >= 3 & (bytes[0] == 0xEF && bytes[1] == 0xBB && bytes[2] == 0xBF))
             return EncodingType.Utf8;
          
          if (bytesRead == 4) { 
             var value = BitConverter.ToUInt32(bytes, 0);
             if (value == 0x0000FEFF | value == 0xFEFF0000)
                return EncodingType.Utf32;
          }
          
          var value16 = BitConverter.ToUInt16(bytes, 0);
          if (value16 == (ushort)0xFEFF | value16 == (ushort)0xFFFE) 
             return EncodingType.Utf16;
          
          return EncodingType.Unknown;
       }
    }
    // The example displays the following output:
    //    Unhandled Exception: System.NotSupportedException: Stream does not support reading.
    //       at System.IO.Stream.BeginReadInternal(Byte[] buffer, Int32 offset, Int32 count, AsyncCallback callback, Object state,
    //     Boolean serializeAsynchronously)
    //       at System.IO.FileStream.BeginRead(Byte[] array, Int32 offset, Int32 numBytes, AsyncCallback userCallback, Object stat
    //    eObject)
    //       at System.IO.Stream.<>c.<BeginEndReadAsync>b__43_0(Stream stream, ReadWriteParameters args, AsyncCallback callback, O
    //    bject state)
    //       at System.Threading.Tasks.TaskFactory`1.FromAsyncTrim[TInstance,TArgs](TInstance thisRef, TArgs args, Func`5 beginMet
    //    hod, Func`3 endMethod)
    //       at System.IO.Stream.BeginEndReadAsync(Byte[] buffer, Int32 offset, Int32 count)
    //       at System.IO.FileStream.ReadAsync(Byte[] buffer, Int32 offset, Int32 count, CancellationToken cancellationToken)
    //       at System.IO.Stream.ReadAsync(Byte[] buffer, Int32 offset, Int32 count)
    //       at FileUtilities.GetEncodingType(FileStream fs)
    //       at Example.Main()
    
    Imports System.IO
    Imports System.Threading.Tasks
    
    Module Example
       Public Sub Main()
          Dim name As String = ".\TestFile.dat"
          Dim fs As New FileStream(name, 
                                   FileMode.Create,
                                   FileAccess.Write)
          Console.WriteLine("Filename: {0}, Encoding: {1}", 
                            name, FileUtilities.GetEncodingType(fs))
       End Sub
    End Module
    
    Public Class FileUtilities
       Public Enum EncodingType As Integer
          None = 0
          Unknown = -1
          Utf8 = 1
          Utf16 = 2
          Utf32 = 3
       End Enum
       
       Public Shared Function GetEncodingType(fs As FileStream) As EncodingType
          Dim bytes(3) As Byte
          Dim t As Task(Of Integer) = fs.ReadAsync(bytes, 0, 4)
          t.Wait()
          Dim bytesRead As Integer = t.Result
          If bytesRead < 2 Then Return EncodingType.None
          
          If bytesRead >= 3 And (bytes(0) = &hEF AndAlso bytes(1) = &hBB AndAlso bytes(2) = &hBF) Then
             Return EncodingType.Utf8
          End If
          
          If bytesRead = 4 Then 
             Dim value As UInteger = BitConverter.ToUInt32(bytes, 0)
             If value = &h0000FEFF Or value = &hFEFF0000 Then
                Return EncodingType.Utf32
             End If
          End If
          
          Dim value16 As UInt16 = BitConverter.ToUInt16(bytes, 0)
          If value16 = &hFEFF Or value16 = &hFFFE Then 
             Return EncodingType.Utf16
          End If
          
          Return EncodingType.Unknown
       End Function
    End Class
    ' The example displays the following output:
    '    Unhandled Exception: System.NotSupportedException: Stream does not support reading.
    '       at System.IO.Stream.BeginReadInternal(Byte[] buffer, Int32 offset, Int32 count, AsyncCallback callback, Object state,
    '     Boolean serializeAsynchronously)
    '       at System.IO.FileStream.BeginRead(Byte[] array, Int32 offset, Int32 numBytes, AsyncCallback userCallback, Object stat
    '    eObject)
    '       at System.IO.Stream.<>c.<BeginEndReadAsync>b__43_0(Stream stream, ReadWriteParameters args, AsyncCallback callback, O
    '    bject state)
    '       at System.Threading.Tasks.TaskFactory`1.FromAsyncTrim[TInstance,TArgs](TInstance thisRef, TArgs args, Func`5 beginMet
    '    hod, Func`3 endMethod)
    '       at System.IO.Stream.BeginEndReadAsync(Byte[] buffer, Int32 offset, Int32 count)
    '       at System.IO.FileStream.ReadAsync(Byte[] buffer, Int32 offset, Int32 count, CancellationToken cancellationToken)
    '       at System.IO.Stream.ReadAsync(Byte[] buffer, Int32 offset, Int32 count)
    '       at FileUtilities.GetEncodingType(FileStream fs)
    '       at Example.Main()
    

    You can eliminate the exception by examining the value of the FileStream.CanRead property and exiting the method if the stream is read-only.

       public static EncodingType GetEncodingType(FileStream fs)
       {
          if (!fs.CanRead) 
             return EncodingType.Unknown;
    
          Byte[] bytes = new Byte[4];
          var t = fs.ReadAsync(bytes, 0, 4);
          t.Wait();
          int bytesRead = t.Result;
          if (bytesRead < 2)
             return EncodingType.None;
          
          if (bytesRead >= 3 & (bytes[0] == 0xEF && bytes[1] == 0xBB && bytes[2] == 0xBF))
             return EncodingType.Utf8;
          
          if (bytesRead == 4) { 
             var value = BitConverter.ToUInt32(bytes, 0);
             if (value == 0x0000FEFF | value == 0xFEFF0000)
                return EncodingType.Utf32;
          }
          
          var value16 = BitConverter.ToUInt16(bytes, 0);
          if (value16 == (ushort)0xFEFF | value16 == (ushort)0xFFFE) 
             return EncodingType.Utf16;
          
          return EncodingType.Unknown;
       }
    }
    // The example displays the following output:
    //       Filename: .\TestFile.dat, Encoding: Unknown
    
    Public Class FileUtilities
       Public Enum EncodingType As Integer
          None = 0
          Unknown = -1
          Utf8 = 1
          Utf16 = 2
          Utf32 = 3
       End Enum
       
       Public Shared Function GetEncodingType(fs As FileStream) As EncodingType
          If Not fs.CanRead Then
             Return EncodingType.Unknown
    
          Dim bytes(3) As Byte
          Dim t As Task(Of Integer) = fs.ReadAsync(bytes, 0, 4)
          t.Wait()
          Dim bytesRead As Integer = t.Result
          If bytesRead < 2 Then Return EncodingType.None
          
          If bytesRead >= 3 And (bytes(0) = &hEF AndAlso bytes(1) = &hBB AndAlso bytes(2) = &hBF) Then
             Return EncodingType.Utf8
          End If
          
          If bytesRead = 4 Then 
             Dim value As UInteger = BitConverter.ToUInt32(bytes, 0)
             If value = &h0000FEFF Or value = &hFEFF0000 Then
                Return EncodingType.Utf32
             End If
          End If
          
          Dim value16 As UInt16 = BitConverter.ToUInt16(bytes, 0)
          If value16 = &hFEFF Or value16 = &hFFFE Then 
             Return EncodingType.Utf16
          End If
          
          Return EncodingType.Unknown
       End Function
    End Class
    ' The example displays the following output:
    '       Filename: .\TestFile.dat, Encoding: Unknown
    

The NotSupportedException exception is closely related to two other exception types;

NotImplementedException.
This exception is thrown when a method could be implemented but is not, either because the member will be implemented in a later version, the member is not available on a particular platform, or the member belongs to an abstract class and a derived class must provide an implementation.

InvalidOperationException
This exception is thrown in scenarios in which it is generally sometimes possible for the object to perform the requested operation, and the object state determines whether the operation can be performed.

.NET Compact Framework notes

When working with the .NET Compact Framework and using P/Invoke on a native function, this exception may be thrown if:

  • The declaration in managed code is incorrect.

  • The .NET Compact Framework does not support what you are trying to do.

  • The DLL names are mangled on export.

    If a NotSupportedException exception is thrown, check:

  • For any violations of the .NET Compact Framework P/Invoke restrictions.

  • For any arguments that require pre-allocated memory. If these exist, you should pass a reference to an existing variable.

  • That the names of the exported functions are correct. This can be verified with DumpBin.exe.

  • That you are not attempting to pass too many arguments.

Constructors

Not​Supported​Exception()

Initializes a new instance of the NotSupportedException class, setting the Message property of the new instance to a system-supplied message that describes the error. This message takes into account the current system culture.

Not​Supported​Exception(​String)

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

Not​Supported​Exception(​Serialization​Info, ​Streaming​Context)

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

Not​Supported​Exception(​String, ​Exception)

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