Task has a wrong return type

问题

What wrong? and how to fix??I'm trying to learn a new subject in c#-task. and when I run I got error message: Error CS0407 'Task MainWindow.btn1_ClickAsync(object, RoutedEventArgs)' has the wrong return type

 public async Task btn1_ClickAsync(object sender, RoutedEventArgs e)
            {
                txtState.Text = "btn1_Click started";
               await LongRunningFunc1();
                txtState.Text = "btn1_Click finished";

            }

        private async Task LongRunningFunc1()
        {
            txt1.Text = "Processing 1 .....";
            btn1.Content = "Wait";
            await Task.Delay(5000);
            txt1.Text = "Hello From Func1";
            btn1.Content = "Click";
        }

wpf designer:

<Grid>
        <TextBlock Name="txtState" Margin="265,10,274,356"/>
        <TextBlock Name="txt1" Height="50" RenderTransformOrigin="0.966,-0.95" Margin="281,68,320,301"/>
        <TextBlock Name="txt2" Height="50" Margin="253,238,274,131" />
        <Button Name="btn1" Background="Red" Margin="281,127,300,208" Click="btn1_ClickAsync"></Button>
        <Button Name="btn2" Background="Aqua" Margin="298,309,311,27"></Button>
    </Grid>

回答1:

Button click events are one of the few method signatures where async void is acceptable. Change your method to read

public async void btn1_ClickAsync(object sender, RoutedEventArgs e)

and you should be OK.

回答2:

Event handlers need to be async void methods:

public async void btn1_ClickAsync(object sender, RoutedEventArgs e)

回答3:

WPF events are usually RoutedEventHandler, i.e. they have the signature void RoutedEventHandler(object sender, RoutedEventArgs e). Your btn1_ClickAsync doesn't match that, hence the error message.

You can fix it by using public async void btn1_ClickAsync(...). Event handlers are also about the only time you would use an async void function.

回答4:

Since it's an event handler it should be async void

public async void btn1_ClickAsync(object sender, RoutedEventArgs e)

Note that this is against all (actually most) async/Task rules. See async/await - when to return a Task vs void? for details.

来源：https://stackoverflow.com/questions/52024766/task-has-a-wrong-return-type

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