FileStream.EndRead(IAsyncResult) 方法
定义
重要
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等待挂起的异步读操作完成。 （请考虑改用 ReadAsync(Byte[], Int32, Int32, CancellationToken)。）
public:
override int EndRead(IAsyncResult ^ asyncResult);public override int EndRead (IAsyncResult asyncResult);override this.EndRead : IAsyncResult -> intPublic Overrides Function EndRead (asyncResult As IAsyncResult) As Integer参数
- asyncResult
- IAsyncResult
对所等待的挂起异步请求的引用。
返回
从流中读取的字节数，介于 0 和所请求的字节数之间。 流仅在流结尾返回 0，否则在至少有 1 个字节可用之前应一直进行阻止。
例外
asyncResult 为 null。
此 IAsyncResult 对象不是通过对该类调用 BeginRead(Byte[], Int32, Int32, AsyncCallback, Object) 来创建的。
流已关闭或出现了内部错误。
示例
此代码示例是为构造函数提供的较大示例的 FileStream(String, FileMode, FileAccess, FileShare, Int32, Boolean) 一部分。
static void EndReadCallback( IAsyncResult^ asyncResult )
{
State^ tempState = dynamic_cast<State^>(asyncResult->AsyncState);
int readCount = tempState->FStream->EndRead( asyncResult );
int i = 0;
while ( i < readCount )
{
if ( tempState->ReadArray[ i ] != tempState->WriteArray[ i++ ] )
{
Console::WriteLine( "Error writing data." );
tempState->FStream->Close();
return;
}
}
Console::WriteLine( "The data was written to {0} "
"and verified.", tempState->FStream->Name );
tempState->FStream->Close();
// Signal the main thread that the verification is finished.
tempState->ManualEvent->Set();
}
public:
static void EndReadCallback(IAsyncResult asyncResult)
{
State tempState = (State)asyncResult.AsyncState;
int readCount = tempState.FStream.EndRead(asyncResult);
int i = 0;
while(i < readCount)
{
if(tempState.ReadArray[i] != tempState.WriteArray[i++])
{
Console.WriteLine("Error writing data.");
tempState.FStream.Close();
return;
}
}
Console.WriteLine("The data was written to {0} and verified.",
tempState.FStream.Name);
tempState.FStream.Close();
// Signal the main thread that the verification is finished.
tempState.ManualEvent.Set();
}
Private Shared Sub EndReadCallback(asyncResult As IAsyncResult)
Dim tempState As State = _
DirectCast(asyncResult.AsyncState, State)
Dim readCount As Integer = _
tempState.FStream.EndRead(asyncResult)
Dim i As Integer = 0
While(i < readCount)
If(tempState.ReadArray(i) <> tempState.WriteArray(i))
Console.WriteLine("Error writing data.")
tempState.FStream.Close()
Return
End If
i += 1
End While
Console.WriteLine("The data was written to {0} and " & _
"verified.", tempState.FStream.Name)
tempState.FStream.Close()
' Signal the main thread that the verification is finished.
tempState.ManualEvent.Set()
End Sub
注解
在 .NET Framework 4 及更早版本中，你必须使用 和 等方法来 BeginRead EndRead 实现异步文件操作。 这些方法仍可用于 .NET Framework 4.5 以支持旧代码;但是，新的异步方法（如 、、 和 ）可帮助你更轻松地实现异步 ReadAsync WriteAsync CopyToAsync FlushAsync 文件操作。
EndRead 必须完全针对每次对 的调用调用 BeginRead 。 在开始另一个读取之前未能结束读取进程可能会导致意外行为，例如死锁。
此方法重写 EndRead。
EndRead 可以从 中对每个 IAsyncResult 调用 BeginRead 。 调用 EndRead 可指示从流中读取的字节数。 EndRead 将阻止 ，直到 I/O 操作完成。