WPF: Cannot set items of a read-only collection in XAML

Question

The scenario is really simple. I have a read-only collection property of my custom control, and I want set the items of the collection in XAML. Like this:

<l:CustomControl>
   <l:CustomControl.ControlItems>
     <l:CustomItem />
     <l:CustomItem />
  </l:CustomControl.ControlItems>
</l:CustomControl>

The ControlItems property has internal set and public get accessors, and is of type FreezableCollection<CustomItem>.

The thing is that I am getting build errors that say this is not possible because my ControlItems property does not have an accessable set accessor.

As I know, this scenario is supported in WPF (as of .NET3.5SP1). Am I wrong? What might be the problem? This works with Grid.RowDefinitions, I tried adding the DesignerSerializationVisibility attribute but it did not work.

Edit: I noticed that I receive this error only when I have an internal, private or protected set accessor. When I completely remove the accessor, everything builds fine.

Answer 1

OK, let me write something here to mark this as answered. XAML parser cannot add items to your control if it does have an internal, private, or protected set method. The solution is to remove the internal/private/protected set method. If no 'set' method exists, everything is fine. This sounds stupid, but this is the fact.

This issue also did hit one of my teammates, so I guess people must be hitting the same issue.