Question

场景：我有一个ListBox，ListBoxItems有一个DataTemplate。我想要做的是在DataTemplate中放置一个ContextMenu。问题是我希望这个ContextMenu ItemsSource根据窗口中的某些属性而不同。我最初的想法是，我可以将ItemsSource绑定到窗口中的Property，并返回ItemsSource;但是，我似乎无法正确绑定此属性。我相信这是因为我在DataTemplate中，因此DataContext（我相信这是正确的词）是ListBoxItem而不是窗口。我怎样才能将DataTemplate中的ContextMenu绑定到DataTemplate之外的Property。

Answer 1

您可以使用RelativeSource FindAncestor语法

从窗口获取DataContext

<DataTemplate>
  <TextBlock Text="{Binding MyInfo}">
    <TextBlock.ContextMenu>
      <Menu ItemsSource="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}, Path=DataContext.MyContextMenuItems}"/>
    </TextBlock.ContextMenu>
  </TextBlock>
</DataTemplate>

不完全确定，但绑定是正确的...... 如果您的DataContext是另一种对象类型，则只需更改AncestorType（例如，通过UserControl）。

Answer 2

这可能是AttachedProperty的合适人选。基本上你要做的是将ContextMenu包装在UserControl中，然后将依赖属性添加到UserControl。例如：

MyContextMenu.xaml

<UserControl x:Class="MyContextMenu" ...>
  <UserControl.Template>
    <ContextMenu ItemSource="{Binding}" />
  </UserControl.Template>
</UserControl>

MyContextMenu.xaml.cs

public static readonly DependencyProperty MenuItemsSourceProperty = DependencyProperty.RegisterAttached(
  "MenuItemsSource",
  typeof(Object),
  typeof(MyContextMenu),
  new FrameworkPropertyMetadata(false, FrameworkPropertyMetadataOptions.AffectsRender)
);
public static void SetMenuItemsSource(UIElement element, Boolean value)
{
  element.SetValue(MenuItemsSourceProperty, value);
  // assuming you want to change the context menu when the mouse is over an element.
  // use can use other events.  ie right mouse button down if its a right click menu.
  // you may see a perf hit as your changing the datacontext on every mousenter.
  element.MouseEnter += (s, e) => {
    // find your ContextMenu and set the DataContext to value
    var window = element.GetRoot();
    var menu = window.GetVisuals().OfType<MyContextMenu>().FirstOrDefault();
    if (menu != null)
      menu.DataContext = value;
  }
}
public static Object GetMenuItemsSource(UIElement element)
{
  return element.GetValue(MenuItemsSourceProperty);
}

Window1.xaml

<Window ...>
  <Window.Resources>
    <DataTemplate TargetType="ListViewItem">
      <Border MyContextMenu.MenuItemsSource="{Binding Orders}">
        <!-- Others -->
      <Border>
    </DataTemplate>
  </Window.Resources>
  <local:MyContextMenu />
  <Button MyContextMenu.MenuItemsSource="{StaticResource buttonItems}" />
  <ListView ... />
</Window>

VisualTreeHelpers

public static IEnumerable<DependencyObject> GetVisuals(this DependencyObject root)
{
    int count = VisualTreeHelper.GetChildrenCount(root);
    for (int i = 0; i < count; i++)
    {
        var child = VisualTreeHelper.GetChild(root, i);
        yield return child;
        foreach (var descendants in child.GetVisuals())
        {
            yield return descendants;
        }
    }
}

public static DependencyObject GetRoot(this DependencyObject child)
{
    var parent = VisualTreeHelper.GetParent(child)
    if (parent == null)
      return child;
    return parent.GetRoot();
}

此示例未经测试我今晚稍后会看一看并确保其准确无误。

DataTemplate WPF中的外部属性

2 个答案:

MyContextMenu.xaml

MyContextMenu.xaml.cs

Window1.xaml

VisualTreeHelpers