FileStream.EndRead(IAsyncResult) 方法

public:
 override int EndRead(IAsyncResult ^ asyncResult);

public override int EndRead(IAsyncResult asyncResult);

override this.EndRead : IAsyncResult -> int

Public Overrides Function EndRead (asyncResult As IAsyncResult) As Integer

参数

返回

从流中读取的字节数，介于 0 和所请求的字节数之间。 流仅在流的末尾返回 0，否则，它们应阻止，直到至少有 1 个字节可用。

例外

示例

此代码示例是为构造函数提供的大型示例的 FileStream(String, FileMode, FileAccess, FileShare, Int32, Boolean) 一部分。

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();
}

let endReadCallback (asyncResult: IAsyncResult) =
    let tempState = asyncResult.AsyncState :?> State
    let readCount = tempState.FStream.EndRead asyncResult

    let mutable i = 0
    let mutable errored = false

    while i < readCount do
        if tempState.ReadArray[i] <> tempState.WriteArray[i] then
            printfn "Error writing data."
            tempState.FStream.Close()
            errored <- true
            i <- readCount

        i <- i + 1

    printfn $"The data was written to {tempState.FStream.Name} and verified."
    tempState.FStream.Close()
    // Signal the main thread that the verification is finished.
    tempState.ManualEvent.Set() |> ignore

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 和更早版本中，必须使用诸如 BeginRead 和 EndRead 实现异步文件操作等方法。 这些方法仍可在 .NET Framework 4.5 中使用以支持旧代码;但是，新的异步方法（如 ReadAsync、WriteAsync、CopyToAsync 和 FlushAsync）可帮助你更轻松地实现异步文件操作。

EndRead 必须完全为每个调用 BeginRead调用调用。 在开始另一个读取之前未能结束读取过程可能会导致不良行为，例如死锁。

此方法重写 EndRead。

EndRead 可以在每个 IAsyncResult 位置 BeginRead调用 。 调用 EndRead 指示从流中读取的字节数。 EndRead 将在 I/O 操作完成之前阻止。

另请参阅

• 文件和流输入/输出
• 如何：从文件读取文本
• 如何：将文本写入文件
• 异步文件输入/输出 (I/O)