Articolo
11/18/2011

UTF8Encoding.GetEncoder Method

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Obtains an encoder that converts a sequence of Unicode characters into a UTF-8 encoded sequence of bytes.

Namespace: System.Text
Assembly: mscorlib (in mscorlib.dll)

Syntax

'Declaration
Public Overrides Function GetEncoder As Encoder

public override Encoder GetEncoder()

Return Value

Type: System.Text.Encoder
An object that converts a sequence of Unicode characters into a UTF-8 encoded sequence of bytes.

Remarks

The Encoder.GetBytes method converts sequential blocks of characters into sequential blocks of bytes, in a manner similar to the UTF8Encoding.GetBytes method. However, an Encoder object maintains state information between calls so it can correctly encode character sequences that span blocks. The Encoder also preserves trailing characters at the end of data blocks and uses the trailing characters in the next encoding operation. For example, a data block might end with an unmatched high surrogate, and the matching low surrogate might be in the next data block. Therefore, GetDecoder and GetEncoder are useful for operations in which a single set of data spans multiple blocks.

If error detection is enabled, that is, the throwOnInvalidCharacters parameter of the constructor is set to true, error detection is also enabled in the Encoder returned by this method. If error detection is enabled and an invalid sequence is encountered, the state of the encoder is undefined and processing must stop.

Examples

The following example demonstrates how to use the GetEncoder method to obtain an encoder to convert a sequence of characters into a UTF-8 encoded sequence of bytes.

Imports System.Text
Imports Microsoft.VisualBasic.Strings

Class Example

   Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      'Characters:
      ' ChrW(97) = a
      ' ChrW(98) = b
      ' ChrW(99) = c
      ' ChrW(768) = `
      ' ChrW(41120) = valid unicode code point, but not a character
      Dim chars() As Char = {ChrW(97), ChrW(98), ChrW(99), ChrW(768), ChrW(41120)}
      Dim bytes() As Byte

      Dim utf8Encoder As Encoder = Encoding.UTF8.GetEncoder()

      Dim byteCount As Integer = utf8Encoder.GetByteCount(chars, 2, 3, True)
      bytes = New Byte(byteCount - 1) {}
      Dim bytesEncodedCount As Integer = utf8Encoder.GetBytes( _
          chars, 2, 3, bytes, 0, True _
      )

      outputBlock.Text += String.Format("{0} bytes used to encode characters.", bytesEncodedCount) & vbCrLf

      outputBlock.Text &= "Encoded bytes: "
      Dim b As Byte
      For Each b In bytes
         outputBlock.Text += String.Format("[{0}]", b)
      Next b
      outputBlock.Text &= vbCrLf
   End Sub 'Main
End Class 'UTF8EncodingExample

using System;
using System.Text;

class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      Char[] chars = new Char[] { 'a', 'b', 'c', '\u0300', '\ua0a0' };
      Byte[] bytes;

      Encoder utf8Encoder = Encoding.UTF8.GetEncoder();

      int byteCount = utf8Encoder.GetByteCount(chars, 2, 3, true);
      bytes = new Byte[byteCount];
      int bytesEncodedCount = utf8Encoder.GetBytes(chars, 2, 3, bytes, 0, true);

      outputBlock.Text += String.Format(
          "{0} bytes used to encode characters.", bytesEncodedCount
      ) + "\n";

      outputBlock.Text += "Encoded bytes: ";
      foreach (Byte b in bytes)
      {
         outputBlock.Text += String.Format("[{0}]", b);
      }
      outputBlock.Text += "\n";
   }
}

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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