在我的自定义控件中单击按钮时发生异常

Question

我制作了一个UWP自定义模板控件，它包含ICommandBarElement的集合，非常类似于标准的CommandBar控件。问题是，只要我点击我的CommandBar实现中包含的任何AppBarButton，就会发生未处理的异常：“没有支持这样的接口”。

有一些我必须做错，但我不能看到它。下面是定制控件的代码：

public sealed class MyCommandBarControl : ContentControl 
{ 
    public MyCommandBarControl() 
    { 
     this.DefaultStyleKey = typeof(MyCommandBarControl); 

     this.PrimaryCommands = new ObservableCollection<ICommandBarElement>(); 
    } 

    public ObservableCollection<ICommandBarElement> PrimaryCommands 
    { 
     get { return (ObservableCollection<ICommandBarElement>)GetValue(PrimaryCommandsProperty); } 
     set { SetValue(PrimaryCommandsProperty, value); } 
    } 

    /// <summary> 
    /// PrimaryCommands Dependency Property 
    /// </summary> 
    public static readonly DependencyProperty PrimaryCommandsProperty = 
     DependencyProperty.Register(
      "PrimaryCommands", 
      typeof(ObservableCollection<ICommandBarElement>), 
      typeof(MainPage), 
      new PropertyMetadata(null, null)); 


    protected override void OnApplyTemplate() 
    { 
     base.OnApplyTemplate(); 

     var primaryItemsControl = GetTemplateChild("PrimaryItemsControl") as ItemsControl; 
     primaryItemsControl.ItemsSource = this.PrimaryCommands; 

    } 

} 

和相关风格：

<Style TargetType="local:MyCommandBarControl" > 
    <Setter Property="Template"> 
     <Setter.Value> 
      <ControlTemplate TargetType="local:MyCommandBarControl"> 
       <Grid x:Name="LayoutRoot" Background="{TemplateBinding Background}"> 
        <Grid x:Name="ContentRoot" 
          VerticalAlignment="{TemplateBinding VerticalAlignment}" 
          Margin="{TemplateBinding Padding}" 
          Height="{TemplateBinding Height}" 
          Background="{TemplateBinding Background}" 
          Opacity="{TemplateBinding Opacity}"> 

         <Grid.ColumnDefinitions> 
          <ColumnDefinition Width="Auto"/> 
          <ColumnDefinition Width="*"/> 
         </Grid.ColumnDefinitions> 

         <ContentControl 
           x:Name="ContentControl" 
           Content="{TemplateBinding Content}" 
           ContentTemplate="{TemplateBinding ContentTemplate}" 
           ContentTransitions="{TemplateBinding ContentTransitions}" 
           Foreground="{TemplateBinding Foreground}" 
           HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" 
           VerticalAlignment="{TemplateBinding VerticalContentAlignment}" 
           HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}" 
           VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}" 
          IsTabStop="False" 
          Margin="10, 0, 0, 0"/> 

         <ItemsControl 
           x:Name="PrimaryItemsControl" 
           IsTabStop="False" 
           Grid.Column="1" 
           Margin="10, 0, 0, 0" 
           HorizontalAlignment="Right" 
           HorizontalContentAlignment="Right"> 
          <ItemsControl.ItemsPanel> 
           <ItemsPanelTemplate> 
            <StackPanel Orientation="Horizontal" /> 
           </ItemsPanelTemplate> 
          </ItemsControl.ItemsPanel> 
         </ItemsControl> 
        </Grid> 
       </Grid> 
      </ControlTemplate> 
     </Setter.Value> 
    </Setter> 
</Style> 

我已经作出了small project you can download能重现问题。任何帮助解决这个例外，将不胜感激。

Answer 1

为什么不从CommandBar控件继承，并且不需要自己管理PrimaryCommands。

所以，简单地更改您的代码下面就可以解决这一问题：

public sealed class MyCommandBarControl : CommandBar 
{ 
    public MyCommandBarControl() 
    { 
     this.DefaultStyleKey = typeof(MyCommandBarControl); 

     //this.PrimaryCommands = new ObservableCollection<ICommandBarElement>(); 
    } 

    //public ObservableCollection<ICommandBarElement> PrimaryCommands 
    //{ 
    // get { return (ObservableCollection<ICommandBarElement>)GetValue(PrimaryCommandsProperty); } 
    // set { SetValue(PrimaryCommandsProperty, value); } 
    //} 

    ///// <summary> 
    ///// PrimaryCommands Dependency Property 
    ///// </summary> 
    //public static readonly DependencyProperty PrimaryCommandsProperty = 
    // DependencyProperty.Register(
    //  "PrimaryCommands", 
    //  typeof(ObservableCollection<ICommandBarElement>), 
    //  typeof(MainPage), 
    //  new PropertyMetadata(null, null)); 


    protected override void OnApplyTemplate() 
    { 
     base.OnApplyTemplate(); 

     var primaryItemsControl = GetTemplateChild("PrimaryItemsControl") as ItemsControl; 
     primaryItemsControl.ItemsSource = this.PrimaryCommands; 

    } 

} 

[UPDATE1]

我觉得这是基本的类型转换，我们不能看到或者我们必须使用一些接口像ICommandBar，但由于其保护级别，我们无法使用。

如果你确实希望自己实现CommandBar，我认为最好创建自己的Command按钮，而不是使用AppBarButton。 但是你需要确保你有一个坚实的理由来自己做。

例如，如果我使用默认按钮，以下方法将起作用。

public sealed class MyCommandBarControl : ContentControl 
{ 
    public MyCommandBarControl() 
    { 
     this.DefaultStyleKey = typeof(MyCommandBarControl); 

     this.PrimaryCommands = new ObservableCollection<Button>(); 
    } 

    public ObservableCollection<Button> PrimaryCommands 
    { 
     get { return (ObservableCollection<Button>)GetValue(PrimaryCommandsProperty); } 
     set { SetValue(PrimaryCommandsProperty, value); } 
    } 

    /// <summary> 
    /// PrimaryCommands Dependency Property 
    /// </summary> 
    public static readonly DependencyProperty PrimaryCommandsProperty = 
     DependencyProperty.Register(
      "PrimaryCommands", 
      typeof(ObservableCollection<Button>), 
      typeof(MainPage), 
      new PropertyMetadata(null, null)); 


    protected override void OnApplyTemplate() 
    { 
     base.OnApplyTemplate(); 

     var primaryItemsControl = GetTemplateChild("PrimaryItemsControl") as ItemsControl; 
     primaryItemsControl.ItemsSource = this.PrimaryCommands; 

    } 

} 

在MainPage.xaml中

<local:MyCommandBarControl> 
     <local:MyCommandBarControl.Content> 
      <TextBlock Text="My CommandBar" /> 
     </local:MyCommandBarControl.Content> 

     <local:MyCommandBarControl.PrimaryCommands> 
      <Button Content="Pin" Click="PinBarButton_Click" /> 
      <Button Content="UnPin" /> 
      <Button Content="Sync" /> 
      <Button Content="Remove" /> 
     </local:MyCommandBarControl.PrimaryCommands> 
    </local:MyCommandBarControl>