.net - 仅使用 XAML 在左键单击时显示上下文菜单

Question

WPF ContextMenu 的默认行为是在用户右键单击时显示它。我希望当用户单击鼠标左键时显示 ContextMenu。看起来这应该是 ContextMenu 上的一个简单属性，但事实并非如此。

我对其进行了操纵，以便在代码隐藏中处理 LeftMouseButtonDown 事件，然后显示上下文菜单。

我在项目中使用 MVVM，这意味着我对具有上下文菜单的项目使用 DataTemplate。摆脱代码隐藏并找到一种使用 XAML 中的触发器或属性来显示上下文菜单的方法会更加优雅。

对于这个问题有什么想法或解决方案吗？

Answer 1

我刚刚根据 HK1 的答案编写并测试了这个(您还可以在 Attached Properties Overview) 中阅读有关附加属性的信息:

public static class ContextMenuLeftClickBehavior
{
    public static bool GetIsLeftClickEnabled(DependencyObject obj)
    {
        return (bool)obj.GetValue(IsLeftClickEnabledProperty);
    }

    public static void SetIsLeftClickEnabled(DependencyObject obj, bool value)
    {
        obj.SetValue(IsLeftClickEnabledProperty, value);
    }

    public static readonly DependencyProperty IsLeftClickEnabledProperty = DependencyProperty.RegisterAttached(
        "IsLeftClickEnabled", 
        typeof(bool), 
        typeof(ContextMenuLeftClickBehavior), 
        new UIPropertyMetadata(false, OnIsLeftClickEnabledChanged));

    private static void OnIsLeftClickEnabledChanged(object sender, DependencyPropertyChangedEventArgs e)
    {
        var uiElement = sender as UIElement;

        if(uiElement != null) 
        {
            bool IsEnabled = e.NewValue is bool && (bool) e.NewValue;

            if(IsEnabled)
            {
                if(uiElement is ButtonBase)
                    ((ButtonBase)uiElement).Click += OnMouseLeftButtonUp;
                else
                    uiElement.MouseLeftButtonUp += OnMouseLeftButtonUp;
            }
            else
            {
                if(uiElement is ButtonBase)
                    ((ButtonBase)uiElement).Click -= OnMouseLeftButtonUp;
                else
                    uiElement.MouseLeftButtonUp -= OnMouseLeftButtonUp;
            }
        }
    }

    private static void OnMouseLeftButtonUp(object sender, RoutedEventArgs e)
    {
        Debug.Print("OnMouseLeftButtonUp");
        var fe = sender as FrameworkElement;
        if(fe != null)
        {
            // if we use binding in our context menu, then it's DataContext won't be set when we show the menu on left click
            // (it seems setting DataContext for ContextMenu is hardcoded in WPF when user right clicks on a control, although I'm not sure)
            // so we have to set up ContextMenu.DataContext manually here
            if (fe.ContextMenu.DataContext == null)
            {
                fe.ContextMenu.SetBinding(FrameworkElement.DataContextProperty, new Binding { Source = fe.DataContext });
            }

            fe.ContextMenu.IsOpen = true;
        }
    }

}

...

<Button Content="Do All" local:ContextMenuLeftClickBehavior.IsLeftClickEnabled="True" >
    <Button.ContextMenu>
        <ContextMenu>
            <MenuItem Header="Make everything awesome" />
            <MenuItem Header="Control the World" />
        </ContextMenu>
    </Button.ContextMenu>
</Button>

(请注意 OnMouseLeftButtonUp() 方法内的注释)