DecoderReplacementFallback 类

参考

定义

命名空间:: System.Text

程序集:: mscorlib.dll, System.Text.Encoding.dll

程序集:: System.Runtime.dll

程序集:: System.Text.Encoding.dll

程序集:: mscorlib.dll

程序集:: netstandard.dll

重要

一些信息与预发行产品相关，相应产品在发行之前可能会进行重大修改。对于此处提供的信息，Microsoft 不作任何明示或暗示的担保。

为不能转换为输出字符的已编码输入字节序列提供称为“回退”的失败处理机制。回退发出用户指定的替换字符串，而不是已解码的输入字节序列。此类不能被继承。

public ref class DecoderReplacementFallback sealed : System::Text::DecoderFallback

public sealed class DecoderReplacementFallback : System.Text.DecoderFallback

[System.Serializable]
public sealed class DecoderReplacementFallback : System.Text.DecoderFallback

type DecoderReplacementFallback = class
    inherit DecoderFallback

[<System.Serializable>]
type DecoderReplacementFallback = class
    inherit DecoderFallback

Public NotInheritable Class DecoderReplacementFallback
Inherits DecoderFallback

继承: Object

DecoderFallback
DecoderReplacementFallback

属性: SerializableAttribute

示例

下面的代码示例演示了该 DecoderReplacementFallback 类。

// This example demonstrates the DecoderReplacementFallback class.

using namespace System;
using namespace System::Text;

int main()
{ 
    // Create an encoding, which is equivalent to calling the 
    // ASCIIEncoding class constructor. 
    // The DecoderReplacementFallback parameter specifies that the 
    // string "(error)" is to replace characters that cannot be decoded. 
    // An encoder replacement fallback is also specified, but in this code
    // example the encoding operation cannot fail.  

    Encoding^ asciiEncoding = Encoding::GetEncoding("us-ascii",
        gcnew EncoderReplacementFallback("(unknown)"),
        gcnew DecoderReplacementFallback("(error)"));
    String^ inputString = "XYZ";
    String^ decodedString;
    String^ twoNewLines = Environment::NewLine + Environment::NewLine;
    array<Byte>^ encodedBytes = gcnew array<Byte>(
        asciiEncoding->GetByteCount(inputString));
    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);

    // ---------------------------------------------------------------------
    // Encode the input string. 

    Console::WriteLine("Encode the input string...");
    numberOfEncodedBytes = asciiEncoding->GetBytes(inputString, 0,
        inputString->Length, encodedBytes, 0);

    // Display the encoded bytes.
    Console::WriteLine("Encoded bytes in hexadecimal ({0} bytes):{1}", 
        numberOfEncodedBytes, Environment::NewLine);
    for each (Byte b in encodedBytes)
    {
        Console::Write("0x{0:X2} ", b);
    }
    Console::Write(twoNewLines);

    // ---------------------------------------------------------------------

    // Replace the encoded byte sequences for the characters 'X' and 'Z'
    // with the value 0xFF, which is outside the valid range of 0x00 to 0x7F
    // for ASCIIEncoding. The resulting byte sequence is actually the
    // beginning of this code example because it is the input to the decoder
    // operation, and is equivalent to a corrupted or improperly encoded
    // byte sequence. 

    encodedBytes[0] = 0xFF;
    encodedBytes[2] = 0xFF;

    Console::WriteLine("Display the corrupted byte sequence...");
    Console::WriteLine("Encoded bytes in hexadecimal ({0} bytes):{1}", 
        numberOfEncodedBytes, Environment::NewLine);
    for each (Byte b in encodedBytes)
    {
        Console::Write("0x{0:X2} ", b);
    }
    Console::Write(twoNewLines);

    // ---------------------------------------------------------------------
    // Decode the encoded bytes.

    Console::WriteLine("Compare the decoded bytes to the input string...");
    decodedString = asciiEncoding->GetString(encodedBytes);

    // Display the input string and the decoded string for comparison.
    Console::WriteLine("Input string:  \"{0}\"", inputString);
    Console::WriteLine("Decoded string:\"{0}\"", decodedString);
}
/*
This code example produces the following results:

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

Input string (3 characters): "XYZ"
Input string in hexadecimal: 0x58 0x59 0x5A

Encode the input string...
Encoded bytes in hexadecimal (3 bytes):

0x58 0x59 0x5A

Display the corrupted byte sequence...
Encoded bytes in hexadecimal (3 bytes):

0xFF 0x59 0xFF

Compare the decoded bytes to the input string...
Input string:  "XYZ"
Decoded string:"(error)Y(error)"

*/

// This example demonstrates the DecoderReplacementFallback 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 DecoderReplacementFallback parameter specifies that the
// string "(error)" is to replace characters that cannot be decoded.
// An encoder replacement fallback is also specified, but in this code
// example the encoding operation cannot fail.

    Encoding ae = Encoding.GetEncoding(
                  "us-ascii",
                  new EncoderReplacementFallback("(unknown)"),
                  new DecoderReplacementFallback("(error)"));
    string inputString = "XYZ";
    string decodedString;
    string twoNewLines = "\n\n";
    byte[] encodedBytes = new byte[ae.GetByteCount(inputString)];
    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);

// --------------------------------------------------------------------------
// Encode the input string.

    Console.WriteLine("Encode the input string...");
    numberOfEncodedBytes = ae.GetBytes(inputString, 0, inputString.Length,
                                       encodedBytes, 0);

// Display the encoded bytes.
    Console.WriteLine("Encoded bytes in hexadecimal ({0} bytes):\n",
                       numberOfEncodedBytes);
    foreach (byte b in encodedBytes)
        {
        Console.Write("0x{0:X2} ", (int)b);
        }
    Console.Write(twoNewLines);

// --------------------------------------------------------------------------

// Replace the encoded byte sequences for the characters 'X' and 'Z' with the
// value 0xFF, which is outside the valid range of 0x00 to 0x7F for
// ASCIIEncoding. The resulting byte sequence is actually the beginning of
// this code example because it is the input to the decoder operation, and
// is equivalent to a corrupted or improperly encoded byte sequence.

    encodedBytes[0] = 0xFF;
    encodedBytes[2] = 0xFF;

    Console.WriteLine("Display the corrupted byte sequence...");
    Console.WriteLine("Encoded bytes in hexadecimal ({0} bytes):\n",
                       numberOfEncodedBytes);
    foreach (byte b in encodedBytes)
        {
        Console.Write("0x{0:X2} ", (int)b);
        }
    Console.Write(twoNewLines);

// --------------------------------------------------------------------------
// Decode the encoded bytes.

    Console.WriteLine("Compare the decoded bytes to the input string...");
    decodedString = ae.GetString(encodedBytes);

// Display the input string and the decoded string for comparison.
    Console.WriteLine("Input string:  \"{0}\"", inputString);
    Console.WriteLine("Decoded string:\"{0}\"", decodedString);
    }
}
/*
This code example produces the following results:

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

Input string (3 characters): "XYZ"
Input string in hexadecimal: 0x58 0x59 0x5A

Encode the input string...
Encoded bytes in hexadecimal (3 bytes):

0x58 0x59 0x5A

Display the corrupted byte sequence...
Encoded bytes in hexadecimal (3 bytes):

0xFF 0x59 0xFF

Compare the decoded bytes to the input string...
Input string:  "XYZ"
Decoded string:"(error)Y(error)"

*/

' This example demonstrates the DecoderReplacementFallback class.
Imports System.Text

Class Sample
    Public Shared Sub Main() 
        
        ' Create an encoding, which is equivalent to calling the 
        ' ASCIIEncoding class constructor. 
        ' The DecoderReplacementFallback parameter specifies that the 
        ' string "(error)" is to replace characters that cannot be decoded. 
        ' An encoder replacement fallback is also specified, but in this code
        ' example the encoding operation cannot fail.  

        Dim erf As New EncoderReplacementFallback("(unknown)")
        Dim drf As New DecoderReplacementFallback("(error)")
        Dim ae As Encoding = Encoding.GetEncoding("us-ascii", erf, drf)
        Dim inputString As String = "XYZ"
        Dim decodedString As String
        Dim twoNewLines As String = vbCrLf & vbCrLf
        Dim numberOfEncodedBytes As Integer = ae.GetByteCount(inputString)
        ' Counteract the compiler implicitly 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)
        
        ' --------------------------------------------------------------------------
        ' Encode the input string. 
        Console.WriteLine("Encode the input string...")
        numberOfEncodedBytes = ae.GetBytes(inputString, 0, inputString.Length, _
                                           encodedBytes, 0)
        
        ' Display the encoded bytes. 
        ' Each element is converted to an integer with Convert.ToInt32.
        Console.WriteLine("Encoded bytes in hexadecimal ({0} bytes):" & vbCrLf, _
                                                         numberOfEncodedBytes)
        Dim b As Byte
        For Each b In  encodedBytes
            Console.Write("0x{0:X2} ", Convert.ToInt32(b))
        Next b
        Console.Write(twoNewLines)
        
        ' --------------------------------------------------------------------------
        ' Replace the encoded byte sequences for the characters 'X' and 'Z' with the 
        ' value 0xFF, which is outside the valid range of 0x00 to 0x7F for 
        ' ASCIIEncoding. The resulting byte sequence is actually the beginning of 
        ' this code example because it is the input to the decoder operation, and 
        ' is equivalent to a corrupted or improperly encoded byte sequence. 

        encodedBytes(0) = &HFF
        encodedBytes(2) = &HFF
        
        Console.WriteLine("Display the corrupted byte sequence...")
        Console.WriteLine("Encoded bytes in hexadecimal ({0} bytes):" & vbCrLf, _
                           numberOfEncodedBytes)
        For Each b In  encodedBytes
            Console.Write("0x{0:X2} ", Convert.ToInt32(b))
        Next b
        Console.Write(twoNewLines)
        
        ' --------------------------------------------------------------------------
        ' Decode the encoded bytes.
        Console.WriteLine("Compare the decoded bytes to the input string...")
        decodedString = ae.GetString(encodedBytes)
        
        ' Display the input string and the decoded string for comparison.
        Console.WriteLine("Input string:  ""{0}""", inputString)
        Console.WriteLine("Decoded string:""{0}""", decodedString)
    
    End Sub
End Class
'
'This code example produces the following results:
'
'The name of the encoding is "us-ascii".
'
'Input string (3 characters): "XYZ"
'Input string in hexadecimal: 0x58 0x59 0x5A
'
'Encode the input string...
'Encoded bytes in hexadecimal (3 bytes):
'
'0x58 0x59 0x5A
'
'Display the corrupted byte sequence...
'Encoded bytes in hexadecimal (3 bytes):
'
'0xFF 0x59 0xFF
'
'Compare the decoded bytes to the input string...
'Input string:  "XYZ"
'Decoded string:"(error)Y(error)"
'

注解

编码或解码操作失败的一个常见原因是基础编码类不提供字符与等效字节序列之间的映射。例如，对象 ASCIIEncoding 无法解码大于0x7F的字节值。如果无法将输入字节序列转换为输出字符，对象 DecoderReplacementFallback 会将替换字符串发送到输出以表示原始输入字节序列。然后，转换过程继续解码原始输入的其余部分。

对象的替换字符串 DecoderReplacementFallback 由对其类构造函数的调用确定。有两个选项可供选择：

替换为默认字符。如果调用 DecoderReplacementFallback() 构造函数，替换字符为“？” (U+003F) 。
替换为所选字符串。如果调用 DecoderReplacementFallback(String) 构造函数，则提供替换字符串。

此类是两个.NET Framework类之一，用于实现不同的回退策略来处理解码转换失败。另一DecoderFallbackException个类是DecoderExceptionFallback类，在遇到无效字节序列时引发该类。

构造函数

DecoderReplacementFallback()	初始化 DecoderReplacementFallback 类的新实例。
DecoderReplacementFallback(String)	使用指定的替换字符串初始化 DecoderReplacementFallback 类的新实例。

属性

DefaultString	获取作为此 DecoderReplacementFallback 对象的值的替换字符串。
MaxCharCount	获取此 DecoderReplacementFallback 对象的替换字符串中的字符数。

方法

CreateFallbackBuffer()	创建一个 DecoderFallbackBuffer 对象，该对象是用此 DecoderReplacementFallback 对象的替换字符串初始化的。
Equals(Object)	指示指定对象的值是否与等于此 DecoderReplacementFallback 对象的值。
GetHashCode()	检索此 DecoderReplacementFallback 对象的值的哈希代码。
GetType()	获取当前实例的 Type。 (继承自 Object)
MemberwiseClone()	创建当前 Object 的浅表副本。 (继承自 Object)
ToString()	返回表示当前对象的字符串。 (继承自 Object)

适用于

DecoderReplacementFallback 类

定义

示例

注解

构造函数

属性

方法

适用于

另请参阅

其他资源