BC42358：由于此调用未等待，因此在调用完成之前，当前方法的执行将继续执行

2025-07-31

由于此调用未等待，因此在调用完成之前，当前方法的执行将继续执行。请考虑将 Await 运算符应用于调用的结果。

当前方法调用一个异步方法，该方法返回或返回Task<TResult>一个Task，并且不对结果应用 Await 运算符。对异步方法的调用将启动异步任务。但是，由于未 Await 应用任何运算符，程序将继续运行，而无需等待任务完成。在大多数情况下，不需要该行为。调用方法的其他方面通常取决于调用的结果，或者，在从包含调用的方法返回之前，调用方法应完成。

同样重要的问题是，在调用异步方法中引发异常时会发生什么情况。在返回Task Task<TResult>或存储在返回的任务的方法中引发的异常。如果不等待任务或显式检查异常，异常将丢失。如果等待任务，则会重新引发其异常。

最佳做法是，应始终等待呼叫。

默认情况下，此消息是警告。有关隐藏警告或将警告视为错误的详细信息，请参阅在 Visual Basic 中配置警告。

错误 ID： BC42358

解决此警告

仅当确定不想等待异步调用完成并且调用方法不会引发任何异常时，才应考虑取消警告。在这种情况下，可以通过向变量分配调用的任务结果来禁止显示警告。

以下示例演示如何引发警告、如何取消警告以及如何等待调用：

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

在此示例中，如果选择“调用”#1 或“调用”#2，则取消唤醒的异步方法（）在调用方（CalledMethodAsyncCallingMethodAsync）和调用方（StartButton_Click）完成后完成。以下输出中的最后一行显示调用方法完成的时间。在输出中标记完整示例中调用 CallingMethodAsync 的事件处理程序的入口和退出。

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.

示例：

以下 Windows Presentation Foundation （WPF）应用程序包含上一个示例中的方法。以下步骤设置应用程序：

创建 WPF 应用程序并将其命名 AsyncWarning。
在 Visual Studio Code 编辑器中，选择 MainWindow.xaml 选项卡。

如果选项卡不可见，请在 解决方案资源管理器中打开 MainWindow.xaml 的快捷菜单，然后选择“ 查看代码”。

将 MainWindow.xaml 的 XAML 视图中的代码替换为以下代码：

<Window x:Class="MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://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>

包含按钮和文本框的简单窗口显示在 MainWindow.xaml 的设计 视图中。

有关 XAML 设计器的详细信息，请参阅使用 XAML 设计器创建 UI。有关如何生成自己的简单 UI 的信息，请参阅演练的“创建 WPF 应用程序”和“设计简单的 WPF MainWindow”部分：使用 Async 和 Await 访问 Web。

将MainWindow.xaml.vb中的代码替换为以下代码。

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.

选择要运行程序的 F5 键，然后选择 “开始 ”按钮。

预期输出显示在代码末尾。

通过

BC42358：由于此调用未等待，因此在调用完成之前，当前方法的执行将继续执行

解决此警告

示例：

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