System.NotSupportedException 類別
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
相關的例外狀況類型
例外 NotSupportedException 狀況與另外兩種例外狀況類型密切相關:
-
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。
-
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。