title: Task has a wrong return type
body: <p>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:
  <code>Error CS0407 'Task MainWindow.btn1_ClickAsync(object, RoutedEventArgs)' has the wrong return type</code> </p>
  
  <pre><code> 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";
          }
  </code></pre>
  
  <p>wpf designer:</p>
  
  <pre><code>&lt;Grid&gt;
          &lt;TextBlock Name="txtState" Margin="265,10,274,356"/&gt;
          &lt;TextBlock Name="txt1" Height="50" RenderTransformOrigin="0.966,-0.95" Margin="281,68,320,301"/&gt;
          &lt;TextBlock Name="txt2" Height="50" Margin="253,238,274,131" /&gt;
          &lt;Button Name="btn1" Background="Red" Margin="281,127,300,208" Click="btn1_ClickAsync"&gt;&lt;/Button&gt;
          &lt;Button Name="btn2" Background="Aqua" Margin="298,309,311,27"&gt;&lt;/Button&gt;
      &lt;/Grid&gt;
  </code></pre>