是否可以等待调用任务？

Question

有没有办法等待调用任务？

Async Function DoStuff() As Task
    StartDoingOtherStuff()

    ' Doing stuff
End Function

Async Function StartDoingOtherStuff() As Task
    ' Doing stuff

    Await callingTask

    ' Finish up
End Function

注意：我想使任务瘫痪，因为它涉及将文件上传到多个目的地。但我想等待调用任务，在所有上传完成后删除文件。

Answer 1

根据 usr 对Get the current Task instance in an async method body 的回答，您可以这样做：

Private Async Function DoStuff() As Task
    'Capture the resulting task in a variable.
    Dim t As Task = (
        Async Function() As Task
            Console.WriteLine("DoStuff()")

            'First await. Required in order to return the task to 't'.
            Await Task.Delay(1)

            'Disable warnings:
            '    "Because this call is not awaited (...)"
            '    "Variable 't' is used before it has been assigned a value (...)"

#Disable Warning BC42358, BC42104

            'Call other method.
            DoOtherStuff(t)

#Enable Warning BC42358, BC42104

            'Simulate process.
            Await Task.Delay(3000)
        End Function
    ).Invoke()

    'Await if needed.
    Await t
End Function

Private Async Function DoOtherStuff(ByVal ParentTask As Task) As Task
    Console.WriteLine("DoOtherStuff()")

    'Await parent task.
    Await ParentTask

    Console.WriteLine("DoStuff() finished!")
End Function

通过使用 lambda 表达式，您可以捕获当前任务，然后将其传递给自身。 Await Task.Delay(1) 是必需的，以便异步方法返回其任务，以便可以将其设置为变量。但是，如果在调用 DoOtherStuff() 之前已经有另一个 await，则可以将其删除。