System.NotSupportedException 類別

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01/04/2024

本文提供此 API 參考文件的補充備註。

NotSupportedException 表示叫用的方法或屬性沒有任何實作存在。

NotSupportedException 會使用具有值0x80131515的 HRESULT COR_E_NOTSUPPORTED。

如需執行個體的初始屬性值的清單NotSupportedException，請參閱NotSupportedException建構函式。

擲回 NotSupportedException 例外狀況

在下列情況下，您可能會考慮擲回 NotSupportedException 例外狀況：

您正在實作一般用途介面，而且方法的數目沒有有意義的實作。例如，如果您要建立實作介面的 IConvertible 日期和時間類型，則會針對大部分轉換擲回 NotSupportedException 例外狀況。
您已繼承自需要覆寫許多方法的抽象類。不過，您只準備提供這些子集的實作。對於您決定不實作的方法，您可以選擇擲回 NotSupportedException。
您正在定義一般用途類型，其狀態會有條件地啟用作業。例如，您的類型可以是唯讀或讀寫。在此情況下：
- 如果對像是只讀的，嘗試將值指派給實例的屬性，或呼叫修改實例狀態的方法應該會擲回 NotSupportedException 例外狀況。
- 您應該實作屬性，這個屬性會 Boolean 傳回值，指出是否提供特定功能。例如，對於可以是唯讀或讀寫的類型，您可以實 IsReadOnly 作屬性，指出一組讀寫方法是否可用或無法使用。

處理 NotSupportedException 例外狀況

例外 NotSupportedException 狀況表示方法沒有實作，而且您不應該呼叫它。您不應該處理例外狀況。相反地，您應該執行的動作取決於例外狀況的原因：實作完全不存在，或成員調用與物件的目的不一致（例如對只讀FileStream物件上方法的呼叫FileStream.Write）。

尚未提供實作，因為作業無法以有意義的方式執行。 當您在物件上呼叫方法時，這是常見的例外狀況，該物件會提供抽象基類方法的實作，或實作一般用途介面，而且方法沒有有意義的實作。

例如，類別 Convert 會實作 IConvertible 介面，這表示它必須包含方法，將每個基本類型轉換成其他基本類型。不過，許多轉換都不可能。因此，例如，呼叫 Convert.ToBoolean(DateTime) 方法會擲回NotSupportedException例外狀況，因為與 Boolean 值之間DateTime沒有可能的轉換

若要排除例外狀況，您應該排除方法呼叫。

指定物件的狀態時，不支援方法呼叫。 您嘗試叫用因為物件狀態而無法使用其功能的成員。您可以使用下列三種方式之一來消除例外狀況：

您事先知道物件的狀態，但您已叫用不支援的方法或屬性。在此情況下，成員調用是錯誤，而且您可以加以消除。

您事先知道物件的狀態（通常是因為您的程式代碼已具現化它），但對象設定錯誤。下列範例說明此問題。它會建立唯讀 FileStream 物件，然後嘗試寫入它。

using System;
using System.IO;
using System.Text;
using System.Threading.Tasks;

public class Example
{
    public static async Task 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));
        await t2;
        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()

open System.IO
open System.Text

let main = task {
    let enc = Encoding.Unicode
    let value = "This is a string to persist."
    let bytes  = enc.GetBytes value

    let fs = new FileStream(@".\TestFile.dat", FileMode.Open, FileAccess.Read)
    let t = fs.WriteAsync(enc.GetPreamble(), 0, enc.GetPreamble().Length)
    let t2 = t.ContinueWith(fun a -> fs.WriteAsync(bytes, 0, bytes.Length))
    let! _ = t2
    fs.Close()
}
main.Wait()

// 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 <StartupCode:fs>.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()

Ycan 可藉由確保具現化物件支援您想要的功能來消除例外狀況。下列範例會藉由提供正確的自變數給FileStream.FileStream(String, FileMode, FileAccess)建構函式，來解決唯讀FileStream對象的問題。

您事先不知道物件的狀態，而且對象不支援特定作業。在大部分情況下，對象應該包含屬性或方法，指出它是否支援一組特定的作業。您可以檢查物件的值，並只在適當時叫用成員，以排除例外狀況。

下列範例會 DetectEncoding 定義方法，這個方法會在嘗試從不支援讀取存取的數據流開頭讀取時擲回 NotSupportedException 例外狀況。

using System;
using System.IO;
using System.Threading.Tasks;

public class TestPropEx1
{
    public static async Task Main()
    {
        String name = @".\TestFile.dat";
        var fs = new FileStream(name,
                                FileMode.Create,
                                FileAccess.Write);
        Console.WriteLine("Filename: {0}, Encoding: {1}",
                          name, await FileUtilities1.GetEncodingType(fs));
    }
}

public class FileUtilities1
{
    public enum EncodingType
    { None = 0, Unknown = -1, Utf8 = 1, Utf16 = 2, Utf32 = 3 }

    public async static Task<EncodingType> GetEncodingType(FileStream fs)
    {
        Byte[] bytes = new Byte[4];
        int bytesRead = await fs.ReadAsync(bytes, 0, 4);
        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.FileStream.BeginRead(Byte[] array, Int32 offset, Int32 numBytes, AsyncCallback callback, Object state)
//       at System.IO.Stream.<>c.<BeginEndReadAsync>b__46_0(Stream stream, ReadWriteParameters args, AsyncCallback callback, Object state)
//       at System.Threading.Tasks.TaskFactory`1.FromAsyncTrim[TInstance, TArgs](TInstance thisRef, TArgs args, Func`5 beginMethod, 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) in C:\Work\docs\program.cs:line 26
//       at Example.Main() in C:\Work\docs\program.cs:line 13
//       at Example.<Main>()

open System
open System.IO

module FileUtilities =
    type EncodingType =
        | None = 0
        | Unknown = -1
        | Utf8 = 1
        | Utf16 = 2
        | Utf32 = 3

    let getEncodingType (fs: FileStream) = 
        task {
            let bytes = Array.zeroCreate<byte> 4
            let! bytesRead = fs.ReadAsync(bytes, 0, 4)
            if bytesRead < 2 then
                return EncodingType.None

            elif bytesRead >= 3 && bytes[0] = 0xEFuy && bytes[1] = 0xBBuy && bytes[2] = 0xBFuy then
                return EncodingType.Utf8
            else
                let value = BitConverter.ToUInt32(bytes, 0)
                if bytesRead = 4 && (value = 0x0000FEFFu || value = 0xFEFF0000u) then
                    return EncodingType.Utf32
                else
                    let value16 = BitConverter.ToUInt16(bytes, 0)
                    if value16 = 0xFEFFus || value16 = 0xFFFEus then
                        return EncodingType.Utf16
                    else
                        return EncodingType.Unknown
        }

let main _ = 
    task {
        let name = @".\TestFile.dat"
        let fs = new FileStream(name, FileMode.Create, FileAccess.Write)
        let! et = FileUtilities.getEncodingType fs
        printfn $"Filename: {name}, Encoding: {et}"
    }

// The example displays the following output:
//    Unhandled Exception: System.NotSupportedException: Stream does not support reading.
//       at System.IO.FileStream.BeginRead(Byte[] array, Int32 offset, Int32 numBytes, AsyncCallback callback, Object state)
//       at System.IO.Stream.<>c.<BeginEndReadAsync>b__46_0(Stream stream, ReadWriteParameters args, AsyncCallback callback, Object state)
//       at System.Threading.Tasks.TaskFactory`1.FromAsyncTrim[TInstance, TArgs](TInstance thisRef, TArgs args, Func`5 beginMethod, 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()
//       at Example.<Main>()

Imports System.IO
Imports System.Threading.Tasks

Module Example2
    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, FileUtilities2.GetEncodingType(fs))
    End Sub
End Module

Public Class FileUtilities2
    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 = &HFEFF 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 FileUtilities2.GetEncodingType(FileStream fs)
'       at Example.Main()

如果數據流是只讀的 FileStream.CanRead ，您可以檢查屬性的值並結束方法，藉此消除例外狀況。

    public static async Task<EncodingType> GetEncodingType(FileStream fs)
    {
        if (!fs.CanRead)
            return EncodingType.Unknown;

        Byte[] bytes = new Byte[4];
        int bytesRead = await fs.ReadAsync(bytes, 0, 4);
        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

let getEncodingType (fs: FileStream) = 
    task {
        if not fs.CanRead then
            return EncodingType.Unknown
        else
            let bytes = Array.zeroCreate<byte> 4
            let! bytesRead = fs.ReadAsync(bytes, 0, 4)
            if bytesRead < 2 then
                return EncodingType.None

            elif bytesRead >= 3 && bytes[0] = 0xEFuy && bytes[1] = 0xBBuy && bytes[2] = 0xBFuy then
                return EncodingType.Utf8
            else
                let value = BitConverter.ToUInt32(bytes, 0)
                if bytesRead = 4 && (value = 0x0000FEFFu || value = 0xFEFF0000u) then
                    return EncodingType.Utf32
                else
                    let value16 = BitConverter.ToUInt16(bytes, 0)
                    if value16 = 0xFEFFus || value16 = 0xFFFEus then
                        return EncodingType.Utf16
                    else
                        return EncodingType.Unknown
    }
// The example displays the following output:
//       Filename: .\TestFile.dat, Encoding: Unknown

Public Class FileUtilities3
    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
        End If

        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 = &HFEFF 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

例外 NotSupportedException 狀況與另外兩種例外狀況類型密切相關：

NotImplementedException

當方法可以實作但不是時，就會擲回這個例外狀況，可能是因為成員將在較新的版本中實作、特定平臺上無法使用成員，或是成員屬於抽象類，且衍生類別必須提供實作。
InvalidOperationException

這個例外狀況會在物件執行要求作業的案例中擲回，而且對象狀態決定是否可以執行作業。

.NET Compact Framework 附注

使用 .NET Compact Framework 並在原生函式上使用 P/Invoke 時，如果：

Managed 程式碼中的宣告不正確。
.NET Compact Framework 不支援您嘗試執行的動作。
DLL 名稱在輸出期間損壞。

NotSupportedException如果擲回例外狀況，請檢查：

針對 .NET Compact Framework P/Invoke 限制的任何違規。
需要預先配置記憶體的任何引數。如果這些引數存在的話，您必須將參考傳遞至現有變數。
輸出函式的所有名稱都是正確的。這可以使用 DumpBin.exe進行驗證。
您並未嘗試傳遞過多的引數。

System.NotSupportedException 類別

擲回 NotSupportedException 例外狀況

處理 NotSupportedException 例外狀況

.NET Compact Framework 附注

意見反應

其他資源

System.NotSupportedException 類別

擲回 NotSupportedException 例外狀況

處理 NotSupportedException 例外狀況

相關的例外狀況類型

.NET Compact Framework 附注

意見反應

其他資源