Duplicate Dependency Property Registration

Question

Here is my UserControl:

Public Class Categories
   Inherits UserControl
   ....
   Private ReadOnly AddSplitProperty As DependencyProperty = DependencyProperty.Register("AddSplit", GetType(Boolean), GetType(Categories))

   Public Property AddSplit As Boolean
      Get
         Return CBool(GetValue(AddSplitProperty))
      End Get
      Set(value As Boolean)
         SetValue(AddSplitProperty, value)
   End Property

End Class

The class Categories is used in a different Window as follows (PIM is the name of the application):

<Window

<Window
....
	xmlns:self="clr-namespace:PIM"
....
    <self:Categories AddSplit="True" />
....
</Window>

Running the application results in the following error:

System.ArgumentException
  HResult=0x80070057
  Message='AddSplit' property was already registered by 'Categories'.
  Source=WindowsBase

(The above is supposed to be a quote but it gets saved as code.)

Apparently, 'AddSplit' is trying to be registered twice. Why?

Answer 1

Registering a DependencyProperty in instance field is trying to register it every time that instance is created.

It should be shared field.

Private Shared ReadOnly AddSplitProperty As DependencyProperty = DependencyProperty.Register("AddSplit", GetType(Boolean), GetType(Categories))

Answer 2

Probably another property uses the same parameter “AddSplit” by mistake.