如何动态更改CommandBar中图像的来源？

Question

经过深入的互联网搜索一天后，我试着直接问你...

我在C＃中编写了一个Windows 10 UWP应用程序。我想展示无线连接的实力。我有几张图片来展示这一点。 WiFi强度应该显示在TopAppBar中。

我用MVVM设置图像源。它适用于UserControl中的图像，但我无法在CommandBar中显示图像。

我有一个事件给我的实际图像的Uri（“图片”）。

private void WiFiInformationUpdated(object sender, WiFiInformationEventArgs args) 
    { 
     if (args.SSID != _viewModel.WifiInformationData.SSID) 
     { 
      _viewModel.WifiInformationData.SSID = args.SSID; 
     } 

     if (args.SignalBars != _viewModel.WifiInformationData.SignalBars) 
     { 
      _viewModel.WifiInformationData.SignalBars = args.SignalBars; 
     } 

     if(args.Picture != null) 
     { 
      Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal,() => 
      { 
       var pic = new BitmapImage(args.Picture); 
       _viewModel.WifiInformationData.Picture = pic; 
      } 
      ); 
     } 
    } 

这是它的用户控件内正常工作：

<UserControl.DataContext> 
    <Binding Path="Main" Source="{StaticResource Locator}"/> 
</UserControl.DataContext> 
<Image Source="{Binding WifiInformationData.Picture}" Grid.Row="1" Grid.Column="2" DataContextChanged="Image_DataContextChanged"/> 

，这是有问题的场景：

<Page.DataContext> 
    <Binding Path="Main" Source="{StaticResource Locator}"/> 
</Page.DataContext> 
<Page.TopAppBar> 
    <CommandBar HorizontalContentAlignment="Center" IsOpen="True" IsSticky="True" CompositeMode="Inherit"> 
     <CommandBar.ContentTemplate> 
      <DataTemplate> 
       <RelativePanel VerticalAlignment="Stretch" Width="200" > 
        <Image Source="{Binding Main.WifiInformationData.Picture, Source={StaticResource Locator}}" Width="20" RelativePanel.Below="tbPercentWifi" DataContextChanged="Image_DataContextChanged"/> 
       </RelativePanel> 
      </DataTemplate> 
     </CommandBar.ContentTemplate>       
    </CommandBar> 
</Page.TopAppBar> 

有什么建议吗？

Answer 1

的解决方案是：

的DataTemplate访问问题...由固定：

public static class DataTemplateObjects 
{ 
    public static DependencyObject FindChildControl<T>(DependencyObject control, string ctrlName) 
    { 
     int childNumber = VisualTreeHelper.GetChildrenCount(control); 
     for (int i = 0; i < childNumber; i++) 
     { 
      DependencyObject child = VisualTreeHelper.GetChild(control, i); 
      FrameworkElement fe = child as FrameworkElement; 
      // Not a framework element or is null 
      if (fe == null) return null; 

      if (child is T && fe.Name == ctrlName) 
      { 
       // Found the control so return 
       return child; 
      } 
      else 
      { 
       // Not found it - search children 
       DependencyObject nextLevel = FindChildControl<T>(child, ctrlName); 
       if (nextLevel != null) 
        return nextLevel; 
      } 
     } 
     return null; 
    } 
} 

，然后在我的事件中的图片来源：

private void WiFiInformationUpdated(object sender, WiFiInformationEventArgs args) 
    { 
     if (args.SSID != _viewModel.WifiInformationData.SSID) 
     { 
      _viewModel.WifiInformationData.SSID = args.SSID; 
     } 

     if (args.SignalBars != _viewModel.WifiInformationData.SignalBars) 
     { 
      _viewModel.WifiInformationData.SignalBars = args.SignalBars; 
     } 

     if(args.Picture != null) 
     { 
      Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal,() => 
      { 
       var pic = new BitmapImage(args.Picture); 
       _viewModel.WifiInformationData.Picture = pic; 
       Image img = DataTemplateObjects.FindChildControl<Image>(commandBar, "imgWifi") as Image; 
       if (img == null) return; 
       img.Source = pic; 
      }); 
     } 
    }