FileStream.EndRead(IAsyncResult) 方法

定義

命名空間:

System.IO

組件:

netstandard.dll, System.Runtime.dll

來源:

FileStream.cs

等待即將完成的非同步讀取操作。 （考慮改用 ReadAsync(Byte[], Int32, Int32, CancellationToken) 。）

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

參數

asyncResult

IAsyncResult

指待處理的非同步請求，需等待。

傳回

Int32

從串流讀取的位元組數，介於 0 與你請求的位元組數之間。 串流只會在串流結束時回傳 0，否則應該封鎖直到至少有 1 位元組可用。

例外狀況

ArgumentNullException

asyncResult 是 null。

ArgumentException

這個 IAsyncResult 物件並非透過呼叫 BeginRead(Byte[], Int32, Int32, AsyncCallback, Object) 這個類別所建立。

InvalidOperationException

EndRead(IAsyncResult) 被多次呼叫。

IOException

串流已關閉或發生內部錯誤。

範例

此程式碼範例是建構子更大範例 FileStream(String, FileMode, FileAccess, FileShare, Int32, Boolean) 的一部分。

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

備註

在 .NET Framework 4 及更早版本中，你必須使用像 BeginRead 和 EndRead 這樣的方法來實作非同步檔案操作。 這些方法仍可在 .NET Framework 4.5 中提供，以支援舊有程式碼;然而，新的非同步方法如 ReadAsync、WriteAsync、CopyToAsync 及 FlushAsync，能幫助你更輕鬆地實作非同步檔案操作。

EndRead 必須在每次呼叫 BeginRead時精確地呼叫。 未能在開始下一個讀取前結束讀取程序，可能導致不理想的行為，如死結。

這個方法會覆寫 EndRead。

EndRead 可從 中呼叫 IAsyncResultBeginRead。 呼叫 EndRead 會告訴你從串流讀取了多少位元組。 EndRead 會在 I/O 操作完成前阻塞。

另請參閱

• 檔案和數據流 I/O
• 如何：從檔案讀取文字
• 如何：將文字寫入檔案
• 非同步檔案 I/O