EncoderExceptionFallback 类
定义
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节序列的输入字符提供一个称为“回退”的失败处理机制。 如果输入字符无法转换为输出字节序列，则回退会引发异常。 此类不能被继承。
public ref class EncoderExceptionFallback sealed : System::Text::EncoderFallbackpublic sealed class EncoderExceptionFallback : System.Text.EncoderFallback[System.Serializable]
public sealed class EncoderExceptionFallback : System.Text.EncoderFallbacktype EncoderExceptionFallback = class
inherit EncoderFallback[<System.Serializable>]
type EncoderExceptionFallback = class
inherit EncoderFallbackPublic NotInheritable Class EncoderExceptionFallback
Inherits EncoderFallback- 继承
- 属性
示例
下面的代码示例演示 EncoderExceptionFallback 了这些和 EncoderFallbackException 类。
// 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. ***
'
注解
编码将 Unicode 字符映射到编码的字节序列，该序列随后可以传输到物理介质，例如磁盘或通信链接。 可以通过各种方式映射字符，特定编码由派生自类的类型 Encoding 表示。 具体而言，编码类型的方法将 GetBytes 字符编码为字节序列，方法将 GetChars 字节序列解码为字符。
如果输入字符不能由编码表示，编码操作可能会失败。 例如， ASCIIEncoding 对象无法对生成超出 U+0000 到 U+007F 范围的 Unicode 代码点值的字符进行编码。
如果无法执行编码或解码转换，.NET Framework提供称为回退的故障处理机制。 应用程序可以使用预定义的.NET Framework编码器回退，也可以创建派生自和EncoderFallbackBuffer类的EncoderFallback自定义编码器回退。
.NET Framework提供了两个预定义类，用于实现不同的回退策略来处理编码转换失败。 该 EncoderReplacementFallback 类替换为无法转换的任何输入字符提供的字符串。 替换字符串将编码为代替无效字符，然后编码操作继续转换输入的其余部分。 相反，类 EncoderExceptionFallback 会在 EncoderFallbackException 遇到无效字符时引发。
构造函数
| EncoderExceptionFallback() |
初始化 EncoderExceptionFallback 类的新实例。 |
属性
| MaxCharCount |
获取此实例可以返回的最大字符数。 |
方法
| CreateFallbackBuffer() |
返回编码器回退缓冲区，如果无法将字符序列转换为字节序列，则该缓冲区引发异常。 |
| Equals(Object) |
指示当前 EncoderExceptionFallback 对象与指定对象是否相等。 |
| GetHashCode() |
检索此实例的哈希代码。 |
| 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) |