DefaultStyleKeyProperty second time

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VB

WPF

dependency

Hi,

I used this tool as Kenneth Haugland recommended me:

WPF-Drawing-Canvas-Control

and I have a problem that I guess is pretty simple..

On the class DrawingCanvas there's a custom control

#Region "Constructor"
    Sub New()
        DefaultStyleKeyProperty.OverrideMetadata(GetType(DrawingCanvas), _
               New FrameworkPropertyMetadata(GetType(DrawingCanvas)))

.....

Public Shared canvaseventproperty As DependencyProperty =   
  DependencyProperty.Register("canvasevent", GetType(selecteddrawingevent), GetType(DrawingCanvas), new propertymatadata()) ....

In my project there's more than this one window and according to a chosed param in window "x", the window "drawingcanvascontrol" opens with a certain picture.
On the first time there's no problem but when I go back to the previous window ("x") and it navigates to "drawingcanvascontrol" I get this error:

"PropertyMetadata property is already registered for the type 'DrawingCanvas' "

what may be the problem?

thanks!