无法将Observable Collection绑定到UserControl上的Attached属性

Question

I want to bind an ObservableCollection of custom type (BoundItem) to a view.

I am using it this way :

<v:MyUserControlBase x:Class="My.Views.MyView"
         (...)
         h:FrameworkElementDropBehavior.MyItems="{Binding Attachments}">

Attachments is defined in the ViewModel as :

public ObservableCollection<BoundItem> Attachments 
{ 
   get { return _Attachments; } 
   set { _Attachments = value; } 
}

My view is an actual DependencyObject since when I do in the code behind of the view the following piece of code:

MessageBox.Show((this as DependencyObject).ToString());

it shows "True".

I defined my Dependency Property that way:

    public static readonly DependencyProperty MyItemsProperty = DependencyProperty.RegisterAttached("MyItems", typeof(ObservableCollection<BoundItem>), typeof(MyView), new FrameworkPropertyMetadata(null));
    public static string GetMyItems(DependencyObject element)
    {
        if (element == null) throw new ArgumentNullException("MyItems");
        return (ObservableCollection<BoundItem>)element.GetValue(MyItemsProperty);
    }
    public static void SetMyItems(DependencyObject element, ObservableCollection<BoundItem> value)
    {
        if (element == null) throw new ArgumentNullException("MyItems");
        element.SetValue(MyItemsProperty, value);
    }

The error that occurs is:

A 'Binding' cannot be set on the 'SetMyItems' property of type 'MyView'. A 'Binding' can only be set on a DependencyProperty of a DependencyObject.

Thanks for you help :) .x

Answer 1

Problem is with your property registration. Instead of owner type MyView it should be FrameworkElementDropBehavior i,e the class where you are defining your property.

public static readonly DependencyProperty MyItemsProperty =
     DependencyProperty.RegisterAttached("MyItems", 
                                        typeof(ObservableCollection<BoundItem>), 
                                        typeof(FrameworkElementDropBehavior), 
                                        new FrameworkPropertyMetadata(null));

Answer 2

此外，SetMyItems第二个参数应为ObservableCollection类型，GetMyItems应具有返回类型ObservableCollection。