如何将 ApplicationCommands 绑定到 ViewModel? [英] How to bind ApplicationCommands to a ViewModel?

问题描述

我已经使用 MVVM-Light 成功地使用了一些自定义命令，但我希望我的应用程序响应标准 ApplicationCommands，不仅在窗口级别，而且在详细的项目级别.

I have successfully used a few custom commands using MVVM-Light, but I want my application to respond to the standard ApplicationCommands, not just at a Window level, but at a detailed item level as well.

我有一个 TreeView，我希望能够在其中复制和粘贴节点.每个 TreeViewItem 都有自己的 ViewModel，它们通过 XAML 中的 HierarchicalDataTemplates 显示为有几种不同的类型.我已经在我的 ViewModel 类上实现了复制、粘贴以及 CanCopy 和 CanPaste 的方法.如果合适，我可以很容易地实现指向这些的 MVVM-Light RelayCommands，但这似乎不对.

I have a TreeView that I want to be able to copy and paste nodes in. Each TreeViewItem has its own ViewModel, and they are displayed via HierarchicalDataTemplates in XAML as there are several different types. I have implemented methods to copy, paste, as well as CanCopy and CanPaste on my ViewModel classes. If appropriate, I could implement MVVM-Light RelayCommands pointing to these easily enough, but that doesn't seem right.

我想使用菜单、Ctrl+C 和 Ctrl+V 或最终使用上下文菜单访问命令.我也不想破坏 UI 中其他元素的复制/粘贴功能，例如文本框.为此目的使用内置的 ApplicationCommands 似乎是合适的.但是，我只看到在 UserControl 代码隐藏中处理这些的示例.我没有(或需要)UserControl，也没有真正遵循 MVVM.

I would like to access the commands using a menu, Ctrl+C and Ctrl+V, or eventually a context menu. I also don't want to break copy/paste functionality for other elements in my UI, such as TextBoxes. It seems appropriate to use the built-in ApplicationCommands for this purpose. However, I am only seeing examples of these being handled in a UserControl code-behind. I don't have (or otherwise need) a UserControl, nor is that really following MVVM.

有什么方法可以将 ApplicationCommand.Copy 和 ApplicationCommand.Paste 命令绑定到我的 ViewModel，即在数据模板中?

Is there a way I can bind ApplicationCommand.Copy and ApplicationCommand.Paste commands to my ViewModels, i.e., in the data templates?

推荐答案

我已经使用附加到 TreeView 的行为解决了这个问题.TreeViewItems 或模板似乎没有将命令路由到它们.幸运的是，TreeView 还有一个 SelectedItem 属性，可以用来获取 ViewModel！

I have resolved this using Behaviors attached to the TreeView. The TreeViewItems or Templates to not seem to get the commands routed to them. Fortunately, the TreeView also has a SelectedItem property that can be used to get the ViewModel!

(行为在概念上类似于@Natxo 答案中链接中的解决方案，但它并不能解决所有问题.)

(Behaviors are conceptually similar to the solution in the link in @Natxo's answer, but it doesn't resolve everything.)

行为类:

public class TreeViewClipboardBehavior : Behavior<TreeView>
{
    protected override void OnAttached()
    {
        base.OnAttached();

        CommandBinding CopyCommandBinding = new CommandBinding(
            ApplicationCommands.Copy,
            CopyCommandExecuted,
            CopyCommandCanExecute);
        AssociatedObject.CommandBindings.Add(CopyCommandBinding);

        CommandBinding CutCommandBinding = new CommandBinding(
            ApplicationCommands.Cut,
            CutCommandExecuted,
            CutCommandCanExecute);
        AssociatedObject.CommandBindings.Add(CutCommandBinding);

        CommandBinding PasteCommandBinding = new CommandBinding(
            ApplicationCommands.Paste,
            PasteCommandExecuted,
            PasteCommandCanExecute);
        AssociatedObject.CommandBindings.Add(PasteCommandBinding);
    }

    private void CopyCommandExecuted(object target, ExecutedRoutedEventArgs e)
    {
        NestingItemTreeViewModelBase item = AssociatedObject.SelectedItem as NestingItemTreeViewModelBase;
        if (item != null && item.CanCopyToClipboard)
        {
            item.CopyToClipboard();
            e.Handled = true;
        }
    }

    private void CopyCommandCanExecute(object target, CanExecuteRoutedEventArgs e)
    {
        NestingItemTreeViewModelBase item = AssociatedObject.SelectedItem as NestingItemTreeViewModelBase;
        if (item != null)
        {
            e.CanExecute = item.CanCopyToClipboard;
            e.Handled = true;
        }
    }

    private void CutCommandExecuted(object target, ExecutedRoutedEventArgs e)
    {
        NestingItemTreeViewModelBase item = AssociatedObject.SelectedItem as NestingItemTreeViewModelBase;
        if (item != null && item.CanCutToClipboard)
        {
            item.CutToClipboard();
            e.Handled = true;
        }
    }

    private void CutCommandCanExecute(object target, CanExecuteRoutedEventArgs e)
    {
        NestingItemTreeViewModelBase item = AssociatedObject.SelectedItem as NestingItemTreeViewModelBase;
        if (item != null)
        {
            e.CanExecute = item.CanCutToClipboard;
            e.Handled = true;
        }
    }


    private void PasteCommandExecuted(object target, ExecutedRoutedEventArgs e)
    {
        NestingItemTreeViewModelBase item = AssociatedObject.SelectedItem as NestingItemTreeViewModelBase;
        if (item != null && item.CanPasteFromClipboard)
        {
            item.PasteFromClipboard();
            e.Handled = true;
        }
    }

    private void PasteCommandCanExecute(object target, CanExecuteRoutedEventArgs e)
    {
        NestingItemTreeViewModelBase item = AssociatedObject.SelectedItem as NestingItemTreeViewModelBase;
        if (item != null)
        {
            e.CanExecute = item.CanPasteFromClipboard;
            e.Handled = true;
        }
    }
}

XAML

<TreeView Grid.Row="2" ItemsSource="{Binding SystemTreeRoot}">
    <i:Interaction.Behaviors>
        <local:TreeViewClipboardBehavior/>
    </i:Interaction.Behaviors>
    <TreeView.Resources>
        <HierarchicalDataTemplate DataType="{x:Type local:MyViewModel}" ItemsSource="{Binding Children}">
            <!-- Template content -->
        </HierarchicalDataTemplate>
</TreeView>

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