EncoderExceptionFallback Kelas

Definisi

Ruang nama:

System.Text

Rakitan:

netstandard.dll, System.Runtime.dll

Sumber:

EncoderExceptionFallback.cs

Menyediakan mekanisme penanganan kegagalan, yang disebut fallback, untuk karakter input yang tidak dapat dikonversi ke urutan byte output. Fallback melemparkan pengecualian jika karakter input tidak dapat dikonversi ke urutan byte output. Kelas ini tidak dapat diwariskan.

public ref class EncoderExceptionFallback sealed : System::Text::EncoderFallback

public sealed class EncoderExceptionFallback : System.Text.EncoderFallback

type EncoderExceptionFallback = class
    inherit EncoderFallback

Public NotInheritable Class EncoderExceptionFallback
Inherits EncoderFallback

Warisan

Object

EncoderFallback

EncoderExceptionFallback

Contoh

Contoh kode berikut menunjukkan EncoderExceptionFallback kelas dan EncoderFallbackException .

// 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. ***
'

Keterangan

Pengodean memetakan karakter Unicode ke urutan byte yang dikodekan, yang kemudian dapat ditransfer ke media fisik, seperti disk, atau melalui tautan komunikasi. Karakter dapat dipetakan dengan berbagai cara, dan pengodean tertentu diwakili oleh jenis yang berasal dari Encoding kelas . Secara khusus, metode jenis GetBytes pengodean mengodekan karakter ke urutan byte, dan GetChars metode mendekode urutan byte ke karakter.

Operasi pengodean dapat gagal jika karakter input tidak dapat diwakili oleh pengodean. Misalnya, ASCIIEncoding objek tidak dapat mengodekan karakter yang menghasilkan nilai titik kode Unicode yang berada di luar rentang U+0000 hingga U+007F.

Dalam kasus di mana konversi pengodean atau dekode tidak dapat dilakukan, .NET Framework menyediakan mekanisme penanganan kegagalan yang disebut fallback. Aplikasi Anda dapat menggunakan fallback encoder .NET Framework yang telah ditentukan sebelumnya, atau dapat membuat fallback encoder kustom yang berasal dari kelas EncoderFallback dan EncoderFallbackBuffer.

.NET Framework menyediakan dua kelas yang telah ditentukan sebelumnya yang menerapkan strategi fallback yang berbeda untuk menangani kegagalan konversi pengodean. Kelas EncoderReplacementFallback menggantikan string yang disediakan untuk karakter input apa pun yang tidak dapat dikonversi. String pengganti dikodekan sebagai pengganti karakter yang tidak valid, lalu operasi pengodean terus mengonversi sisa input. Sebaliknya, EncoderExceptionFallback kelas melemparkan EncoderFallbackException ketika karakter yang tidak valid ditemui.

Konstruktor

Nama	Deskripsi
EncoderExceptionFallback()	Menginisialisasi instans baru dari kelas EncoderExceptionFallback.

Properti

Nama	Deskripsi
MaxCharCount	Mendapatkan jumlah maksimum karakter yang dapat dikembalikan instans ini.

Metode

Nama	Deskripsi
CreateFallbackBuffer()	Mengembalikan buffer fallback encoder yang melemparkan pengecualian jika tidak dapat mengonversi urutan karakter menjadi urutan byte.
Equals(Object)	Menunjukkan apakah objek saat ini EncoderExceptionFallback dan objek tertentu sama.
GetHashCode()	Mengambil kode hash untuk instans ini.
GetType()	Mendapatkan Type instans saat ini. (Diperoleh dari Object)
MemberwiseClone()	Membuat salinan dangkal dari Objectsaat ini. (Diperoleh dari Object)
ToString()	Mengembalikan string yang mewakili objek saat ini. (Diperoleh dari Object)

Lihat juga

• Memahami Pengodean