DecoderExceptionFallback 類別
定義
重要
部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。
針對無法轉換為輸入字元的編碼輸入位元組序列，提供失敗處理機制 (稱為後援)。 後援會擲回例外狀況，而不會將輸入位元組序列解碼。 此類別無法獲得繼承。
public ref class DecoderExceptionFallback sealed : System::Text::DecoderFallbackpublic sealed class DecoderExceptionFallback : System.Text.DecoderFallback[System.Serializable]
public sealed class DecoderExceptionFallback : System.Text.DecoderFallbacktype DecoderExceptionFallback = class
inherit DecoderFallback[<System.Serializable>]
type DecoderExceptionFallback = class
inherit DecoderFallbackPublic NotInheritable Class DecoderExceptionFallback
Inherits DecoderFallback- 繼承
- 屬性
範例
下列程式碼範例示範 DecoderExceptionFallback 和 DecoderFallbackException 類別。
// This example demonstrates the DecoderExceptionFallback class.
using namespace System;
using namespace System::Text;
int main()
{
// Create an encoding, which is equivalent to calling the
// ASCIIEncoding class constructor.
// The DecoderExceptionFallback parameter specifies that an exception
// is thrown if a character cannot be encoded.
// An encoder exception fallback is also specified, but in this code
// example the encoding operation cannot fail.
Encoding^ asciiEncoding = Encoding::GetEncoding("us-ascii",
gcnew EncoderExceptionFallback(), gcnew DecoderExceptionFallback());
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);
// ---------------------------------------------------------------------
// Attempt to decode the encoded bytes. However, an exception is thrown
// before the byte sequence can be decoded.
Console::WriteLine("Compare the decoded bytes to the input string...");
try
{
decodedString = asciiEncoding->GetString(encodedBytes);
// This statement is never executed.
Console::WriteLine("This statement is never executed.");
}
catch (DecoderFallbackException^ 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): "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...
System.Text.DecoderFallbackException: Unable to translate bytes [FF] at index 0 from speci
fied code page to Unicode.
at System.Text.DecoderExceptionFallbackBuffer.Throw(Byte[] bytesUnknown, Int32 index)
at System.Text.DecoderExceptionFallbackBuffer.Fallback(Byte[] bytesUnknown, Int32 index
)
at System.Text.DecoderFallbackBuffer.InternalFallback(Byte[] bytes, Byte* pBytes)
at System.Text.ASCIIEncoding.GetCharCount(Byte* bytes, Int32 count, DecoderNLS decoder)
at System.String.CreateStringFromEncoding(Byte* bytes, Int32 byteLength, Encoding encod
ing)
at System.Text.ASCIIEncoding.GetString(Byte[] bytes, Int32 byteIndex, Int32 byteCount)
at System.Text.Encoding.GetString(Byte[] bytes)
at Sample.Main()
*** THE CODE EXAMPLE TERMINATES HERE AS INTENDED. ***
*/
// This example demonstrates the DecoderExceptionFallback 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 DecoderExceptionFallback parameter specifies that an exception
// is thrown if a character cannot be encoded.
// An encoder exception fallback is also specified, but in this code
// example the encoding operation cannot fail.
Encoding ae = Encoding.GetEncoding(
"us-ascii",
new EncoderExceptionFallback(),
new DecoderExceptionFallback());
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);
// --------------------------------------------------------------------------
// Attempt to decode the encoded bytes. However, an exception is thrown
// before the byte sequence can be decoded.
Console.WriteLine("Compare the decoded bytes to the input string...");
try {
decodedString = ae.GetString(encodedBytes);
}
catch (DecoderFallbackException dfe)
{
Console.WriteLine(dfe);
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): "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...
System.Text.DecoderFallbackException: Unable to translate bytes [FF] at index 0 from speci
fied code page to Unicode.
at System.Text.DecoderExceptionFallbackBuffer.Throw(Byte[] bytesUnknown, Int32 index)
at System.Text.DecoderExceptionFallbackBuffer.Fallback(Byte[] bytesUnknown, Int32 index
)
at System.Text.DecoderFallbackBuffer.InternalFallback(Byte[] bytes, Byte* pBytes)
at System.Text.ASCIIEncoding.GetCharCount(Byte* bytes, Int32 count, DecoderNLS decoder)
at System.String.CreateStringFromEncoding(Byte* bytes, Int32 byteLength, Encoding encod
ing)
at System.Text.ASCIIEncoding.GetString(Byte[] bytes, Int32 byteIndex, Int32 byteCount)
at System.Text.Encoding.GetString(Byte[] bytes)
at Sample.Main()
*** THE CODE EXAMPLE TERMINATES HERE AS INTENDED. ***
*/
' This example demonstrates the DecoderExceptionFallback class.
Imports System.Text
Class Sample
Public Shared Sub Main()
' Create an encoding, which is equivalent to calling the
' ASCIIEncoding class constructor.
' The DecoderExceptionFallback parameter specifies that an exception
' is thrown if a character cannot be encoded.
' An encoder exception fallback is also specified, but in this code
' example the encoding operation cannot fail.
Dim eef As New EncoderExceptionFallback()
Dim def As New DecoderExceptionFallback()
Dim ae As Encoding = Encoding.GetEncoding("us-ascii", eef, def)
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 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...")
' Each element is converted to an integer with Convert.ToInt32.
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)
' --------------------------------------------------------------------------
' Attempt to decode the encoded bytes. However, an exception is thrown
' before the byte sequence can be decoded.
Console.WriteLine("Compare the decoded bytes to the input string...")
Try
decodedString = ae.GetString(encodedBytes)
Catch dfe As DecoderFallbackException
Console.WriteLine(dfe)
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): "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...
'System.Text.DecoderFallbackException: Unable to translate bytes [FF] at index 0 from speci
'fied code page to Unicode.
' at System.Text.DecoderExceptionFallbackBuffer.Throw(Byte[] bytesUnknown, Int32 index)
' at System.Text.DecoderExceptionFallbackBuffer.Fallback(Byte[] bytesUnknown, Int32 index
')
' at System.Text.DecoderFallbackBuffer.InternalFallback(Byte[] bytes, Byte* pBytes)
' at System.Text.ASCIIEncoding.GetCharCount(Byte* bytes, Int32 count, DecoderNLS decoder)
'
' at System.String.CreateStringFromEncoding(Byte* bytes, Int32 byteLength, Encoding encod
'ing)
' at System.Text.ASCIIEncoding.GetString(Byte[] bytes, Int32 byteIndex, Int32 byteCount)
' at System.Text.Encoding.GetString(Byte[] bytes)
' 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。
如果輸入位元組序列無法透過編碼對應，解碼作業可能會失敗。 例如， ASCIIEncoding 物件無法解碼位元組序列，其會產生代碼點值超出 U+0000 到 U+007F 的字元。
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解碼器後援，也可以建立衍生自 和 DecoderFallbackBuffer 類別的 DecoderFallback 自訂解碼器後援。
.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解碼轉換失敗。 類別 DecoderReplacementFallback 會取代所提供的字串，取代無法轉換的任何輸入位元組序列。 發出替代字串之後，解碼作業會繼續轉換輸入的其餘部分。 相反地，當遇到不正確位元組序列時，類別 DecoderExceptionFallback 會擲回 DecoderFallbackException 。
建構函式
| DecoderExceptionFallback() |
初始化 DecoderExceptionFallback 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() |
傳回解碼器後援緩衝區，它會在無法將位元組序列轉換成字元時擲回例外狀況。 |
| Equals(Object) |
指示目前的 DecoderExceptionFallback 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) |