Dependency property on custom user control

I have a big issue here. Here's the thing:

I have a custom control which contains a RichTextBox. In this rich text box i introduce hyperlinks and textblocks.

In the user Control I have Property named Designer which returns the serialized flow document from the richtextbox contained in my usercontrol.

public string Designer
    {
        get
        {
            return XamlWriter.Save(linkRtb.Document);
        }
        set
        {
            var stringReader = new StringReader(value);
  开发者_开发问答          var xmlTextReader = new XmlTextReader(stringReader);
            linkRtb.Document = (FlowDocument)XamlReader.Load(xmlTextReader);

            OnPropertyChanged("Designer");
        }
    }

Binding anything to this property works. But what i want to do is to bind this property to something that i have in code behind. The problem is that if I make Designer a dependency property the binding doesn't work and i have no clue why.

The binding that i want to do looks like this:

Designer="{Binding Source=CodeBehindClass, Path=CodeBehindVariable, Mode=OneWayToSource, UpdateSourceTrigger=PropertyChanged}"

From what i have read i understood that you cannot add any logic to the get and set for the dependency property.

Correct, use the PropertyChangedCallback in the metadata upon DP registration instead.