Question

I’m creating a UserControl which will be used in various scenarios. I need to expose a collection of strings from the UserControl and I’m not sure how to do it.

The two possible uses I see are:

• a control on its containing control binds to the collection, e.g. a ListBox;
• a property on the containing control’s ViewModel needs to bind to the collection.

I can get the former to work with a public ObservableCollection<String> property on the UserControl but it won’t work for the latter. (I get “Object of type ‘System.Windows.Data.Binding’ cannot be converted to type ‘System.Collections.ObjectModel.ObservableCollection`1[System.String]’.”)

Is there a solution that will work for both?

EDIT

This is my stab at a UML diagram showing what I’m doing:

Answer 1

I think the problem is just that the binder can’t understand generics. You should be able to get around that by inheriting from ObservableCollection<string> to make a non-generic class. You can use something like this:

class StringCollection : ObservableCollection<string> { }

Since you are using that property as a target of a binding, you must declare it as a DependencyProperty:

class ObjectSelectorView
{
    public StringCollection ObjectNames
    {
        get { return (StringCollection)GetValue(ObjectNamesProperty); }
        set { SetValue(ObjectNamesProperty, value); }
    }

    // Using a DependencyProperty as the backing store for ObjectNames.
    // This enables animation, styling, binding, etc...
    public static readonly DependencyProperty ObjectNamesProperty = 
        DependencyProperty.Register("ObjectNames", typeof(StringCollection),
            typeof(ObjectSelectorView), null);
   ....
}