因為未等候此呼叫，所以在呼叫完成之前會繼續執行目前方法

發行項
06/08/2015

錯誤訊息

因為未等候此呼叫，所以在呼叫完成之前會繼續執行目前方法。應用程式會呼叫的結果" 「Await運算子。

目前方法呼叫的傳回 Task 或 Task ，不應用等候運算子套用至結果的非同步方法。為非同步方法的呼叫開始非同步工作。不過，在中，因為 Await 運算子不適用，程式會繼續執行，而不等候工作完成。在大部分情況下，該行為沒有所需的。通常會呼叫方法的其他方面相依於這個呼叫的結果，或至少，呼叫的方法必須完成，才能從包含呼叫的方法之前傳回。

一樣重要的問題是發生在呼叫的非同步方法引發的例外狀況。在方法傳回 Task 引發或 Task 的例外是這個傳回的工作中。如果沒有等候工作也不會明確檢查例外狀況，例外狀況會遺失。如果您正在等候該工作，其會重新擲回例外狀況。

基於最佳做法，您應該永遠等候呼叫。

根據預設，這是一個警告訊息。如需隱藏警告或將警告視為錯誤的詳細資訊，請參閱在 Visual Basic 中設定警告。

錯誤ID: B C42358

若要解決這個警告

您應該考慮隱藏這個警告，只有在確定您不要等候非同步呼叫完成，呼叫的方法不會引發任何例外狀況。在這種情況下，您可以指定呼叫的工作結果隱藏警告指派給變數。

下列範例顯示如何產生這個警告，如何隱藏及如何等候呼叫。

    Async Function CallingMethodAsync() As Task

        ResultsTextBox.Text &= vbCrLf & "  Entering calling method."

        ' Variable delay is used to slow down the called method so that you
        ' can distinguish between awaiting and not awaiting in the program's output. 
        ' You can adjust the value to produce the output that this topic shows 
        ' after the code.
        Dim delay = 5000

        ' Call #1.
        ' Call an async method. Because you don't await it, its completion isn't 
        ' coordinated with the current method, CallingMethodAsync.
        ' The following line causes the warning.
        CalledMethodAsync(delay)

        ' Call #2.
        ' To suppress the warning without awaiting, you can assign the 
        ' returned task to a variable. The assignment doesn't change how
        ' the program runs. However, the recommended practice is always to
        ' await a call to an async method.
        ' Replace Call #1 with the following line.
        'Task delayTask = CalledMethodAsync(delay)

        ' Call #3
        ' To contrast with an awaited call, replace the unawaited call 
        ' (Call #1 or Call #2) with the following awaited call. The best 
        ' practice is to await the call.

        'Await CalledMethodAsync(delay)

        ' If the call to CalledMethodAsync isn't awaited, CallingMethodAsync
        ' continues to run and, in this example, finishes its work and returns
        ' to its caller.
        ResultsTextBox.Text &= vbCrLf & "  Returning from calling method."
    End Function

    Async Function CalledMethodAsync(howLong As Integer) As Task

        ResultsTextBox.Text &= vbCrLf & "    Entering called method, starting and awaiting Task.Delay."
        ' Slow the process down a little so you can distinguish between awaiting
        ' and not awaiting. Adjust the value for howLong if necessary.
        Await Task.Delay(howLong)
        ResultsTextBox.Text &= vbCrLf & "    Task.Delay is finished--returning from called method."
    End Function

在此範例中，，您還是可以選擇呼叫#1或呼叫#2，在它的呼叫端(CallingMethodAsync)和呼叫端的呼叫端(StartButton_Click)之後unawaited非同步方法(CalledMethodAsync)結束為止。，在呼叫的方法完成時，在下列輸出中的最後一行顯示。從呼叫在完整範例中的 CallingMethodAsync 的事件處理常式的項目與和匯出輸出標示為[]。

Entering the Click event handler.
  Entering calling method.
    Entering called method, starting and awaiting Task.Delay.
  Returning from calling method.
Exiting the Click event handler.
    Task.Delay is finished--returning from called method.

範例

下列Windows Presentation Foundation (WPF)應用程式包含前一個範例中的方法。下列步驟會設定應用程式。

建立WPF應用程式，並將其命名為 AsyncWarning。
在Visual Studio程式碼編輯器中，選取 MainWindow.xaml 索引標籤。

如果這個選項未顯示，請開啟MainWindow.xaml的捷徑功能表上 方案總管，然後選取 檢視程式碼。

以下列程式碼取代MainWindow.xaml XAML 檢視的程式碼。

<Window x:Class="MainWindow"
        xmlns="https://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="https://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Button x:Name="StartButton" Content="Start" HorizontalAlignment="Left" Margin="214,28,0,0" VerticalAlignment="Top" Width="75" HorizontalContentAlignment="Center" FontWeight="Bold" FontFamily="Aharoni" Click="StartButton_Click" />
        <TextBox x:Name="ResultsTextBox" Margin="0,80,0,0" TextWrapping="Wrap" FontFamily="Lucida Console"/>
    </Grid>
</Window>

包含一個按鈕和一個文字方塊的簡單視窗會出現在MainWindow.xaml 設計檢視。

如需XAML設計工具的詳細資訊，請參閱使用 XAML 設計工具建立 UI。如需如何建置的資訊擁有簡單UI，請參閱逐步解說：使用 Async 和 Await 存取 Web (C# 和 Visual Basic)「建立WPF應用程式」和「設計簡單的WPF MainWindow」一節。

以下列程式碼取代MainWindow.xaml.vb的程式碼。

Class MainWindow 

    Private Async Sub StartButton_Click(sender As Object, e As RoutedEventArgs)

        ResultsTextBox.Text &= vbCrLf & "Entering the Click event handler."
        Await CallingMethodAsync()
        ResultsTextBox.Text &= vbCrLf & "Exiting the Click event handler."
    End Sub


    Async Function CallingMethodAsync() As Task

        ResultsTextBox.Text &= vbCrLf & "  Entering calling method."

        ' Variable delay is used to slow down the called method so that you
        ' can distinguish between awaiting and not awaiting in the program's output. 
        ' You can adjust the value to produce the output that this topic shows 
        ' after the code.
        Dim delay = 5000

        ' Call #1.
        ' Call an async method. Because you don't await it, its completion isn't 
        ' coordinated with the current method, CallingMethodAsync.
        ' The following line causes the warning.
        CalledMethodAsync(delay)

        ' Call #2.
        ' To suppress the warning without awaiting, you can assign the 
        ' returned task to a variable. The assignment doesn't change how
        ' the program runs. However, the recommended practice is always to
        ' await a call to an async method.

        ' Replace Call #1 with the following line.
        'Task delayTask = CalledMethodAsync(delay)

        ' Call #3
        ' To contrast with an awaited call, replace the unawaited call 
        ' (Call #1 or Call #2) with the following awaited call. The best 
        ' practice is to await the call.

        'Await CalledMethodAsync(delay)

        ' If the call to CalledMethodAsync isn't awaited, CallingMethodAsync
        ' continues to run and, in this example, finishes its work and returns
        ' to its caller.
        ResultsTextBox.Text &= vbCrLf & "  Returning from calling method."
    End Function

    Async Function CalledMethodAsync(howLong As Integer) As Task

        ResultsTextBox.Text &= vbCrLf & "    Entering called method, starting and awaiting Task.Delay."
        ' Slow the process down a little so you can distinguish between awaiting
        ' and not awaiting. Adjust the value for howLong if necessary.
        Await Task.Delay(howLong)
        ResultsTextBox.Text &= vbCrLf & "    Task.Delay is finished--returning from called method."
    End Function

End Class

' Output

' Entering the Click event handler.
'   Entering calling method.
'     Entering called method, starting and awaiting Task.Delay.
'   Returning from calling method.
' Exiting the Click event handler.
'     Task.Delay is finished--returning from called method.


' Output

' Entering the Click event handler.
'   Entering calling method.
'     Entering called method, starting and awaiting Task.Delay.
'     Task.Delay is finished--returning from called method.
'   Returning from calling method.
' Exiting the Click event handler.

選取按F5鍵執行程式，然後選取啟動按鈕。

預期的輸出會顯示在程式碼結尾。

共用方式為

因為未等候此呼叫，所以在呼叫完成之前會繼續執行目前方法

錯誤訊息

若要解決這個警告

範例

請參閱

參考

概念

其他資源