awaitの前後のコードが2回実行されています

Question

var awaitの前後のコードが2回実行されているかどうかを確認する機能を作成しました。

ボタンをクリックすると、InvokeRefresh()関数が呼び出されますが、var sdfiles = await removableDevices.GetFilesAsync();の行の前後のコードは2回実行されます。

は

コード：

<Page 
    x:Class="App7.MainPage" 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    xmlns:local="using:App7" 
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
    mc:Ignorable="d" 
    Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"> 

    <Grid> 
     <Button x:Name="button" Content="Click me" HorizontalAlignment="Left" Margin="144,261,0,0" VerticalAlignment="Top" Click="button_Click" 
       RenderTransformOrigin="-0.48,0.63"/> 

    </Grid> 
</Page> 



using System; 
using System.Collections.Generic; 
using System.Diagnostics; 
using System.IO; 
using System.Linq; 
using System.Runtime.InteropServices.WindowsRuntime; 
using Windows.Foundation; 
using Windows.Foundation.Collections; 
using Windows.Storage; 
using Windows.UI.Popups; 
using Windows.UI.Xaml; 
using Windows.UI.Xaml.Controls; 
using Windows.UI.Xaml.Controls.Primitives; 
using Windows.UI.Xaml.Data; 
using Windows.UI.Xaml.Input; 
using Windows.UI.Xaml.Media; 
using Windows.UI.Xaml.Navigation; 

// The Blank Page item template is documented at http://go.microsoft.com/fwlink/?LinkId=234238 

namespace App7 
{ 
    /// <summary> 
    /// An empty page that can be used on its own or navigated to within a Frame. 
    /// </summary> 
    public sealed partial class MainPage : Page 
    { 
     public MainPage() 
     { 
      this.InitializeComponent(); 

      this.NavigationCacheMode = NavigationCacheMode.Required; 
     } 

     /// <summary> 
     /// Invoked when this page is about to be displayed in a Frame. 
     /// </summary> 
     /// <param name="e">Event data that describes how this page was reached. 
     /// This parameter is typically used to configure the page.</param> 
     protected override void OnNavigatedTo(NavigationEventArgs e) 
     { 
      // TODO: Prepare page for display here. 

      // TODO: If your application contains multiple pages, ensure that you are 
      // handling the hardware Back button by registering for the 
      // Windows.Phone.UI.Input.HardwareButtons.BackPressed event. 
      // If you are using the NavigationHelper provided by some templates, 
      // this event is handled for you. 
     } 

     private void button_Click(object sender, RoutedEventArgs e) 
     { 
      InvokeRefresh(); 
     } 

     private async void InvokeRefresh() 
     { 
      StorageFolder removableDevices; 
      removableDevices = (await KnownFolders.RemovableDevices.GetFoldersAsync()).FirstOrDefault(); 
      if (removableDevices == null) 
      { 
       MessageDialog mssgboxx1 = new MessageDialog("SD card not found. Add external SD card with downloaded bastas."); 
       await mssgboxx1.ShowAsync(); 
      } 
      else 
      { 
       Debug.WriteLine("before"); 
       var sdfiles = await removableDevices.GetFilesAsync(); 
       var epath = await removableDevices.CreateFolderAsync("ebasta", CreationCollisionOption.OpenIfExists); 
       Debug.WriteLine("after"); 
      } 
     } 
    } 
} 

出力：私はしようとするだろう

前
前 後
後

Answer 1

まず最初は、コードのこのビットを変更です。何らかの理由でボタンが2回クリックされた場合、InvokeRefreshは待つのではなく同時に2回実行されます。

private async void button_Click(object sender, RoutedEventArgs e) 
    { 
     await InvokeRefresh(); 
    } 

また、少し方法を変更する必要があります。

private async Task InvokeRefresh() 

出力