UTF8Encoding.GetPreamble 方法
如果此实例的构造函数请求提供一个字节顺序标记，则返回用 UTF-8 格式编码的 Unicode 字节顺序标记。
**命名空间:**System.Text
**程序集:**mscorlib（在 mscorlib.dll 中）
语法
声明
Public Overrides Function GetPreamble As Byte()
用法
Dim instance As UTF8Encoding
Dim returnValue As Byte()
returnValue = instance.GetPreamble
public override byte[] GetPreamble ()
public:
virtual array<unsigned char>^ GetPreamble () override
public byte[] GetPreamble ()
public override function GetPreamble () : byte[]
返回值
如果此实例的构造函数请求提供字节顺序标记，则返回一个包含 Unicode 字节顺序标记的字节数组。 否则，返回一个长度为零的字节数组。
备注
或者，UTF8Encoding 提供一个前导码（即一个字节数组），可以将它作为编码过程中产生的字节序列的前缀。如果前导码中包含字节顺序标记（码位为 U+FEFF），则它会帮助解码器确定字节顺序和转换格式或 UTF。Unicode 字节顺序标记被序列化为 EF BB BF（十六进制）。GetPreamble 方法返回一个包含字节顺序标记的字节数组。
有关 Unicode 编码、字节顺序和字节顺序标记的更多信息，请参见 www.unicode.org 上的“The Unicode Standard”（Unicode 标准）部分。
警告
若要确保编码后的字节能够正确解码，请在编码后的字节前添加前导码作为前缀。
示例
下面的示例演示了如何使用 GetPreamble 方法返回以 UTF-8 格式编码的 Unicode 字节顺序标记。请注意，UTF8Encoding 的默认构造函数不提供前导码。
Imports System
Imports System.Text
Class UTF8EncodingExample
Public Shared Sub Main()
' The default constructor does not provide a preamble.
Dim UTF8NoPreamble As New UTF8Encoding()
Dim UTF8WithPreamble As New UTF8Encoding(True)
Dim preamble() As Byte
preamble = UTF8NoPreamble.GetPreamble()
Console.WriteLine("UTF8NoPreamble")
Console.WriteLine(" preamble length: {0}", preamble.Length)
Console.Write(" preamble: ")
ShowArray(preamble)
preamble = UTF8WithPreamble.GetPreamble()
Console.WriteLine("UTF8WithPreamble")
Console.WriteLine(" preamble length: {0}", preamble.Length)
Console.Write(" preamble: ")
ShowArray(preamble)
End Sub 'Main
Public Shared Sub ShowArray(theArray As Array)
Dim o As Object
For Each o In theArray
Console.Write("[{0}]", o)
Next o
Console.WriteLine()
End Sub 'ShowArray
End Class 'UTF8EncodingExample
using System;
using System.Text;
class UTF8EncodingExample {
public static void Main() {
// The default constructor does not provide a preamble.
UTF8Encoding UTF8NoPreamble = new UTF8Encoding();
UTF8Encoding UTF8WithPreamble = new UTF8Encoding(true);
Byte[] preamble;
preamble = UTF8NoPreamble.GetPreamble();
Console.WriteLine("UTF8NoPreamble");
Console.WriteLine(" preamble length: {0}", preamble.Length);
Console.Write(" preamble: ");
ShowArray(preamble);
preamble = UTF8WithPreamble.GetPreamble();
Console.WriteLine("UTF8WithPreamble");
Console.WriteLine(" preamble length: {0}", preamble.Length);
Console.Write(" preamble: ");
ShowArray(preamble);
}
public static void ShowArray(Array theArray) {
foreach (Object o in theArray) {
Console.Write("[{0}]", o);
}
Console.WriteLine();
}
}
using namespace System;
using namespace System::Text;
using namespace System::Collections;
void ShowArray( Array^ theArray )
{
IEnumerator^ myEnum = theArray->GetEnumerator();
while ( myEnum->MoveNext() )
{
Object^ o = safe_cast<Object^>(myEnum->Current);
Console::Write( "[{0}]", o );
}
Console::WriteLine();
}
int main()
{
// The default constructor does not provide a preamble.
UTF8Encoding^ UTF8NoPreamble = gcnew UTF8Encoding;
UTF8Encoding^ UTF8WithPreamble = gcnew UTF8Encoding( true );
array<Byte>^preamble;
preamble = UTF8NoPreamble->GetPreamble();
Console::WriteLine( "UTF8NoPreamble" );
Console::WriteLine( " preamble length: {0}", preamble->Length );
Console::Write( " preamble: " );
ShowArray( preamble );
preamble = UTF8WithPreamble->GetPreamble();
Console::WriteLine( "UTF8WithPreamble" );
Console::WriteLine( " preamble length: {0}", preamble->Length );
Console::Write( " preamble: " );
ShowArray( preamble );
}
import System.*;
import System.Text.*;
class UTF8EncodingExample
{
public static void main(String[] args)
{
// The default constructor does not provide a preamble.
UTF8Encoding utf8NoPreamble = new UTF8Encoding();
UTF8Encoding utf8WithPreamble = new UTF8Encoding(true);
ubyte preamble[];
preamble = utf8NoPreamble.GetPreamble();
Console.WriteLine("UTF8NoPreamble");
Console.WriteLine(" preamble length: {0}",
String.valueOf(preamble.length));
Console.Write(" preamble: ");
ShowArray(preamble);
preamble = utf8WithPreamble.GetPreamble();
Console.WriteLine("UTF8WithPreamble");
Console.WriteLine(" preamble length: {0}",
String.valueOf(preamble.length));
Console.Write(" preamble: ");
ShowArray(preamble);
} //main
public static void ShowArray(Array theArray)
{
Object o = null;
for (int iCtr = 0; iCtr < theArray.get_Count(); iCtr++) {
o = theArray.get_Item(iCtr);
Console.Write("[{0}]", o);
}
Console.WriteLine();
} //ShowArray
} //UTF8EncodingExample
平台
Windows 98、Windows 2000 SP4、Windows Millennium Edition、Windows Server 2003、Windows XP Media Center Edition、Windows XP Professional x64 Edition、Windows XP SP2、Windows XP Starter Edition
.NET Framework 并不是对每个平台的所有版本都提供支持。有关受支持版本的列表，请参见系统要求。
版本信息
.NET Framework
受以下版本支持：2.0、1.1、1.0
.NET Compact Framework
受以下版本支持：2.0、1.0