WPF 依赖属性优先级 &引用类型默认值 [英] WPF dependency property precedence & reference type Default Values

问题描述

如果我创建一个这样的自定义控件:

If I create a custom control like this:

public class MyControl : ContentControl
{
   public static readonly DependencyProperty ItemsProperty =               
         DependencyProperty.Register(
                "Items", 
                typeof(ObservableCollection<object>), 
                typeof(MyControl), 
                new PropertyMetadata(null));

   public MyControl()
   {   
       // Setup a default value to empty collection
       // so users of MyControl can call MyControl.Items.Add()
       Items = new ObservableCollection<object>();
   }

   public ObservableCollection<object> Items
   { 
      get { return (ObservableCollection<object>)GetValue(ItemsProperty); } 
      set { SetValue(ItemsProperty, value); } 
   } 
}

然后允许用户像这样在 Xaml 中绑定到它:

And then allow the user to bind to it in Xaml like this:

<DataTemplate>
    <MyControl Items="{Binding ItemsOnViewModel}"/>
</DataTemplate>

然后绑定永远不会起作用！这是由于 Dependency Property Precedence 将 CLR Set值高于模板绑定！

Then the binding never works! This is due to the Dependency Property Precedence, which puts CLR Set values above Template bindings!

所以，我明白为什么这不起作用，但我想知道是否有解决方案.对于只想以编程方式添加项目的 MyControl 的懒惰消费者，是否可以为新的 ObservableCollection 提供 ItemsProperty 的默认值，同时允许 My Control 的 MVVM 高级用户通过 DataTemplate 绑定到相同的属性?

So, I understand why this isn't working, but I wonder if there is a solution. Is it possible to provide a default value of ItemsProperty to new ObservableCollection for lazy consumers of MyControl that just want to add Items programmatically, while allowing MVVM power-users of My Control to bind to the same property via a DataTemplate?

这是为了 Silverlight &WPF.样式中的 DynamicResource setter 似乎是一个解决方案，但不适用于 Silverlight :(

This is for Silverlight & WPF. DynamicResource setter in a style seemed like a solution but that won't work for Silverlight :(

更新:

我可以确认 SetCurrentValue(ItemsProperty, new ObservableCollection