EncoderExceptionFallback 類別

定義

針對無法轉換為輸出位元組序列的輸入字元,提供失敗處理機制 (稱為後援)。 如果輸入字元無法轉換成輸出位元組序列,後援會擲回例外狀況。 此類別無法獲得繼承。

public ref class EncoderExceptionFallback sealed : System::Text::EncoderFallback
public sealed class EncoderExceptionFallback : System.Text.EncoderFallback
[System.Serializable]
public sealed class EncoderExceptionFallback : System.Text.EncoderFallback
type EncoderExceptionFallback = class
    inherit EncoderFallback
[<System.Serializable>]
type EncoderExceptionFallback = class
    inherit EncoderFallback
Public NotInheritable Class EncoderExceptionFallback
Inherits EncoderFallback
繼承
EncoderExceptionFallback
屬性

範例

下列程式碼範例示範 EncoderExceptionFallbackEncoderFallbackException 類別。

// This example demonstrates the EncoderExceptionFallback class.

using namespace System;
using namespace System::Text;

int main()
{
    // Create an encoding, which is equivalent to calling the
    // ASCIIEncoding class constructor.
    // The EncoderExceptionFallback parameter causes an exception to
    // be thrown when a character cannot be encoded.
    // A decoder exception fallback is also specified, but it is not
    // used because this example terminates during the encoding operation.

    Encoding^ asciiEncoding = Encoding::GetEncoding("us-ascii",
        gcnew EncoderExceptionFallback(), gcnew DecoderExceptionFallback());

    // The input string consists of the Unicode characters LEFT POINTING
    // DOUBLE ANGLE QUOTATION MARK (U+00AB), 'X' (U+0058), and RIGHT
    // POINTING DOUBLE ANGLE QUOTATION MARK (U+00BB).
    // The encoding can only encode characters in the US-ASCII range of
    // U+0000 through U+007F. Consequently, the characters bracketing the
    // 'X' character cause an exception.
    String^ inputString = L"\u00abX\u00bb";

    String^ twoNewLines = Environment::NewLine + Environment::NewLine;
    array<Byte>^ encodedBytes = gcnew array<Byte>(
        asciiEncoding->GetMaxByteCount(inputString->Length));
    int numberOfEncodedBytes = 0;

    // ---------------------------------------------------------------------
    Console::Clear();

    // Display the name of the encoding.
    Console::WriteLine("The name of the encoding is \"{0}\".{1}",
        asciiEncoding->WebName, Environment::NewLine);

    // Display the input string in text.
    Console::WriteLine("Input string ({0} characters): \"{1}\"",
        inputString->Length, inputString);

    // Display the input string in hexadecimal.
    Console::Write("Input string in hexadecimal: ");
    for each (char c in inputString)
    {
        Console::Write("0x{0:X2} ", c);
    }
    Console::Write(twoNewLines);

    // ---------------------------------------------------------------------
    // Attempt to encode the input string. However, an exception is thrown
    // before the input string can be encoded.

    Console::WriteLine("Encode the input string...");

    // The code example terminates during the call to the GetBytes() method.
    try
    {
        numberOfEncodedBytes = asciiEncoding->GetBytes(inputString, 0,
            inputString->Length, encodedBytes, 0);
        // This statement is never executed.
        Console::WriteLine("This statement is never executed.");
    }
    catch (EncoderFallbackException^ ex)
    {
        Console::WriteLine(ex);
        Console::WriteLine(
            "{0}*** THE CODE EXAMPLE TERMINATES HERE AS INTENDED. ***",
            Environment::NewLine);
    }
}

/*
This code example produces the following results:

The name of the encoding is "us-ascii".

Input string (3 characters): "X"
Input string in hexadecimal: 0xAB 0x58 0xBB

Encode the input string...
System.Text.EncoderFallbackException: Unable to translate Unicode character \u00AB at inde
x 0 to specified code page.
at System.Text.EncoderExceptionFallbackBuffer.Fallback(Char charUnknown, Int32 index)
at System.Text.EncoderFallbackBuffer.InternalFallback(Char ch, Char*& chars)
at System.Text.ASCIIEncoding.GetBytes(Char* chars, Int32 charCount, Byte* bytes, Int32
byteCount, EncoderNLS encoder)
at System.Text.ASCIIEncoding.GetBytes(String chars, Int32 charIndex, Int32 charCount, B
yte[] bytes, Int32 byteIndex)
at Sample.Main()

*** THE CODE EXAMPLE TERMINATES HERE AS INTENDED. ***

*/
// This example demonstrates the EncoderExceptionFallback class.

using System;
using System.Text;

class Sample
{
    public static void Main()
    {

// Create an encoding, which is equivalent to calling the
// ASCIIEncoding class constructor.
// The EncoderExceptionFallback parameter causes an exception to
// be thrown when a character cannot be encoded.
// A decoder exception fallback is also specified, but it is not
// used because this example terminates during the encoding operation.

    Encoding ae = Encoding.GetEncoding(
                  "us-ascii",
                  new EncoderExceptionFallback(),
                  new DecoderExceptionFallback());

// The input string consists of the Unicode characters LEFT POINTING
// DOUBLE ANGLE QUOTATION MARK (U+00AB), 'X' (U+0058), and RIGHT POINTING
// DOUBLE ANGLE QUOTATION MARK (U+00BB).
// The encoding can only encode characters in the US-ASCII range of U+0000
// through U+007F. Consequently, the characters bracketing the 'X' character
// cause an exception.
    string inputString = "\u00abX\u00bb";

    string twoNewLines = "\n\n";
    byte[] encodedBytes = new byte[ae.GetMaxByteCount(inputString.Length)];
    int numberOfEncodedBytes = 0;

// --------------------------------------------------------------------------
    Console.Clear();

// Display the name of the encoding.
    Console.WriteLine("The name of the encoding is \"{0}\".\n", ae.WebName);

// Display the input string in text.
    Console.WriteLine("Input string ({0} characters): \"{1}\"",
                       inputString.Length, inputString);

// Display the input string in hexadecimal.
    Console.Write("Input string in hexadecimal: ");
    foreach (char c in inputString.ToCharArray()) {
        Console.Write("0x{0:X2} ", (int)c);}
    Console.Write(twoNewLines);

// --------------------------------------------------------------------------
// Attempt to encode the input string. However, an exception is thrown before
// the input string can be encoded.

    Console.WriteLine("Encode the input string...");

// The code example terminates during the call to the GetBytes() method.
    try {
        numberOfEncodedBytes = ae.GetBytes(inputString, 0, inputString.Length,
                                           encodedBytes, 0);
        }
    catch (EncoderFallbackException e)
        {
        Console.WriteLine(e);
        Console.WriteLine("\n*** THE CODE EXAMPLE TERMINATES HERE AS INTENDED. ***");
        return;
        }

// This statement is never executed.
    Console.WriteLine("This statement is never executed.");
    }
}
/*
This code example produces the following results:

The name of the encoding is "us-ascii".

Input string (3 characters): "«X»"
Input string in hexadecimal: 0xAB 0x58 0xBB

Encode the input string...
System.Text.EncoderFallbackException: Unable to translate Unicode character \u00AB at inde
x 0 to specified code page.
   at System.Text.EncoderExceptionFallbackBuffer.Fallback(Char charUnknown, Int32 index)
   at System.Text.EncoderFallbackBuffer.InternalFallback(Char ch, Char*& chars)
   at System.Text.ASCIIEncoding.GetBytes(Char* chars, Int32 charCount, Byte* bytes, Int32
byteCount, EncoderNLS encoder)
   at System.Text.ASCIIEncoding.GetBytes(String chars, Int32 charIndex, Int32 charCount, B
yte[] bytes, Int32 byteIndex)
   at Sample.Main()

*** THE CODE EXAMPLE TERMINATES HERE AS INTENDED. ***

*/
' This example demonstrates the EncoderExceptionFallback class.
Imports System.Text

Class Sample
    Public Shared Sub Main() 
        
        ' Create an encoding, which is equivalent to calling the 
        ' ASCIIEncoding class constructor. 
        ' The EncoderExceptionFallback parameter causes an exception to
        ' be thrown when a character cannot be encoded. 
        ' A decoder exception fallback is also specified, but it is not 
        ' used because this example terminates during the encoding operation.  


        Dim eef As New EncoderExceptionFallback()
        Dim def As New DecoderExceptionFallback()
        Dim ae As Encoding = Encoding.GetEncoding("us-ascii", eef, def)
        
        ' The input string consists of the Unicode characters LEFT POINTING 
        ' DOUBLE ANGLE QUOTATION MARK (U+00AB), 'X' (U+0058), and RIGHT POINTING 
        ' DOUBLE ANGLE QUOTATION MARK (U+00BB). 
        ' The encoding can only encode characters in the US-ASCII range of U+0000 
        ' through U+007F. Consequently, the characters bracketing the 'X' character
        ' cause an exception.

        Dim inputString As String = "«X»"
        
        Dim twoNewLines As String = vbCrLf & vbCrLf
        Dim numberOfEncodedBytes As Integer = ae.GetMaxByteCount(inputString.Length)
        ' Counteract the compiler adding an extra element.
        Dim encodedBytes(numberOfEncodedBytes - 1) As Byte
        
        ' --------------------------------------------------------------------------
        Console.Clear()
        
        ' Display the name of the encoding.
        Console.WriteLine("The name of the encoding is ""{0}""." & vbCrLf, ae.WebName)
        
        ' Display the input string in text.
        Console.WriteLine("Input string ({0} characters): ""{1}""", _
                           inputString.Length, inputString)
        
        ' Display the input string in hexadecimal. 
        ' Each element is converted to an integer with Convert.ToInt32.
        Console.Write("Input string in hexadecimal: ")
        Dim c As Char
        For Each c In  inputString.ToCharArray()
            Console.Write("0x{0:X2} ", Convert.ToInt32(c))
        Next c
        Console.Write(twoNewLines)
        
        ' --------------------------------------------------------------------------
        ' Attempt to encode the input string. However, an exception is thrown before
        ' the input string can be encoded.
        Console.WriteLine("Encode the input string...")
        
        ' The code example terminates during the call to the GetBytes() method.
        Try
            numberOfEncodedBytes = ae.GetBytes(inputString, 0, inputString.Length, _
                                               encodedBytes, 0)
        Catch e As EncoderFallbackException
            Console.WriteLine(e)
            Console.WriteLine(vbCrLf & _
                              "*** THE CODE EXAMPLE TERMINATES HERE AS INTENDED. ***")
            Return
        End Try
        
        ' This statement is never executed.
        Console.WriteLine("This statement is never executed.")
    
    End Sub
End Class
'
'This code example produces the following results:
'
'The name of the encoding is "us-ascii".
'
'Input string (3 characters): "X"
'Input string in hexadecimal: 0xAB 0x58 0xBB
'
'Encode the input string...
'System.Text.EncoderFallbackException: Unable to translate Unicode character \u00AB at inde
'x 0 to specified code page.
'   at System.Text.EncoderExceptionFallbackBuffer.Fallback(Char charUnknown, Int32 index)
'   at System.Text.EncoderFallbackBuffer.InternalFallback(Char ch, Char*& chars)
'   at System.Text.ASCIIEncoding.GetBytes(Char* chars, Int32 charCount, Byte* bytes, Int32
'byteCount, EncoderNLS encoder)
'   at System.Text.ASCIIEncoding.GetBytes(String chars, Int32 charIndex, Int32 charCount, B
'yte[] bytes, Int32 byteIndex)
'   at Sample.Main()
'
'*** THE CODE EXAMPLE TERMINATES HERE AS INTENDED. ***
'

備註

編碼會將 Unicode 字元對應至編碼的位元組序列,之後可以傳輸至實體媒體,例如磁片或透過通訊連結。 字元可以透過各種方式對應,而特定編碼方式是由衍生自 類別的類型 Encoding 來表示。 具體而言,編碼類型的 GetBytes 方法會將字元編碼為位元組序列,而 方法會將 GetChars 位元組序列解碼為字元。

如果輸入字元無法由編碼表示,編碼作業可能會失敗。 例如, ASCIIEncoding 物件無法編碼產生超出 U+0000 至 U+007F 範圍的 Unicode 字碼點值。

如果無法執行編碼或解碼轉換,.NET Framework會提供稱為後援的失敗處理機制。 您的應用程式可以使用預先定義的.NET Framework編碼器後援,也可以建立衍生自 和 EncoderFallbackBuffer 類別的 EncoderFallback 自訂編碼器後援。

.NET Framework提供兩個預先定義的類別,可實作不同的後援策略來處理編碼轉換失敗。 類別 EncoderReplacementFallback 會取代提供給任何無法轉換之輸入字元的字串。 替代字串會編碼來取代不正確字元,然後編碼作業會繼續轉換輸入的其餘部分。 相反地,當遇到無效字元時,類別 EncoderExceptionFallback 會擲回 EncoderFallbackException

建構函式

EncoderExceptionFallback()

初始化 EncoderExceptionFallback 類別的新執行個體。

屬性

MaxCharCount

取得這個執行個體可以傳回的最大字元數。

方法

CreateFallbackBuffer()

傳回編碼器後援緩衝區,它會在無法將字元序列轉換成位元組序列時擲回例外狀況。

Equals(Object)

指示目前的 EncoderExceptionFallback 物件和指定的物件是否相等。

GetHashCode()

擷取這個執行個體的雜湊碼。

GetType()

取得目前執行個體的 Type

(繼承來源 Object)
MemberwiseClone()

建立目前 Object 的淺層複製。

(繼承來源 Object)
ToString()

傳回代表目前物件的字串。

(繼承來源 Object)

適用於

另請參閱