C# WPF Caliburn Micro TreeViewItem.Expanded 事件未触发

Question

我正在使用 Caliburn Micro Message.Attach 通过 XAML 尝试将事件绑定(bind)到 View 模型，但我无法获得 TreeViewItem.Expanded事件触发。其他事件如 SetSelectedItem工作正常。

我在 SO here 上发现了另一个问题但这对我的情况没有帮助，因为没有提供响应的上下文。

我能找到的唯一其他信息是以下 GitHub issue .

Internally Caliburn.Micro turns <Button cm:Message.Attach="[Event Click] = [Action Test]" />

into

<Button>
   <i:Interaction.Triggers>
       <i:EventTrigger EventName="Click">
           <cm:ActionMessage MethodName="Test" />
       </i:EventTrigger>
   </i:Interaction.Triggers>
</Button>

As you noted, EventTrigger doesn't support attached events. A quick look around brought up How to attached an MVVM EventToCommand to an Attached event which shows how to create a RoutedEventTrigger that you could plug into the full syntax.

同样，我尝试了这种方法，但不完全理解如何实现它。它在自定义类中触发事件，但永远不会传递给我在 View 模型中的处理程序。

这是我的 XAML(没有 GitHub 建议):

    <TreeView x:Name="FolderView"
                              cal:Message.Attach="[Event TreeViewItem.Expanded] = [Action Expanded($this)]; 
                              [Event SelectedItemChanged] = [Action SetSelectedItem($this.SelectedItem)]">
                        <TreeView.Resources>
                            <HierarchicalDataTemplate DataType="{x:Type models:LogicalDriveItem}" 
                                                      ItemsSource="{Binding Directories}"  >
                                <StackPanel Orientation="Horizontal">
                                    <TextBlock VerticalAlignment="Center" Text="{Binding Path=DriveLetter}"></TextBlock>
                                </StackPanel>
                            </HierarchicalDataTemplate>
                            <HierarchicalDataTemplate DataType="{x:Type models:DirectoryItem}"
                                                      ItemsSource="{Binding Directories}">
                                <TextBlock VerticalAlignment="Center" Text="{Binding Path=Path}"></TextBlock>
                            </HierarchicalDataTemplate>
                        </TreeView.Resources>
                    </TreeView>

我的 View 模型代码:

    public void Expanded(object sender, RoutedEventArgs e)
    {
        // This won't fire
    }

    public void Expanded(object sender)
    {
        // Or this
    }

    public void SetSelectedItem(object sender)
    {
        // But this will
    }

Answer 1

mm8 提供的链接解决了我的问题。

该问题中的 OP 使用的是我在 GitHub 上找到的相同 RoutedEventTrigger 帮助器类，但他们的答案提供的额外上下文很有帮助。使用 RoutedEventTrigger 帮助器类，我将 XAML 更新为以下内容:

<i:Interaction.Triggers>
                    <!--in the routed event property you need to put the full name space and event name-->
                    <helpers:RoutedEventTrigger RoutedEvent="TreeViewItem.Expanded">
                        <cal:ActionMessage MethodName="Expanded">
                            <cal:Parameter Value="$eventArgs" />
                        </cal:ActionMessage>
                    </helpers:RoutedEventTrigger>
                </i:Interaction.Triggers>

现在成功地在 ViewModel 代码中触发了我的事件。

请注意， $this 对我不起作用，因为我的数据项是字符串。就我而言，它是文件资源管理器样式的 TreeView 。对于上下文，这是完整的 XAML:

<TreeView x:Name="FolderView">
                <i:Interaction.Triggers>
                    <!--in the routed event property you need to put the full name space and event name-->
                    <helpers:RoutedEventTrigger RoutedEvent="TreeViewItem.Expanded">
                        <cal:ActionMessage MethodName="Expanded">
                            <cal:Parameter Value="$eventArgs" />
                        </cal:ActionMessage>
                    </helpers:RoutedEventTrigger>
                </i:Interaction.Triggers>
                <TreeView.Resources>
                    <HierarchicalDataTemplate DataType="{x:Type models:LogicalDriveItem}" 
                                              ItemsSource="{Binding Directories}"  >
                        <StackPanel Orientation="Horizontal">
                            <!--<Image MaxWidth="20" Source="Images/Image.png"/>-->
                            <TextBlock VerticalAlignment="Center" Text="{Binding Path=DriveLetter}"></TextBlock>
                        </StackPanel>
                    </HierarchicalDataTemplate>
                    <HierarchicalDataTemplate DataType="{x:Type models:DirectoryItem}"
                                              ItemsSource="{Binding Directories}">
                        <TextBlock VerticalAlignment="Center" Text="{Binding Path=Name}"></TextBlock>
                    </HierarchicalDataTemplate>
                </TreeView.Resources>
            </TreeView>