Question

I was under the impression that CLR wrappers for dependency properties were optional under WPF, and just useful for setting within your own code.

However, I have created a UserControl without wrappers, but some XAML that uses it will not compile without them:

namespace MyControlLib
{
    public partial class MyControl : UserControl
    {
        public static readonly DependencyProperty SomethingProperty;

        static MyControl()
        {
            SomethingProperty = DependencyProperty.Register("Something", typeof(int), typeof(MyControl));
        }
    }
}

XAML usage:

<Window  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:ctrl="clr-namespace:MyControlLib;assembly=MyControlLib">

   <ctrl:MyControl Something="45" />

</Window>

Trying to compile this gives:

error MC3072: The property ‘Something’ does not exist in XML namespace ‘clr-namespace:MyControlLib’. Line blah Position blah.

Adding a CLR wrapper in MyControl.xaml.cs like:

public int Something
{
    get { return (int)GetValue(SomethingProperty); }
    set { SetValue(SomethingProperty, value); }
}

means it all compiles and works fine.

What am I missing?

Answer 1

You could use dependency properties without wrappers inside runtime bindings, but to set the property like you want you must have C# property to allow xaml compiler to compile your code.