We are not sure what exactly you are trying to achieve in your application. If you want to animate the RadRibbonBackstage you can use an attached property to trigger a custom animation for the RadRibbonBackstage control. You can also define attached property to take and use the width of the ribbon in the animations. Basically, you can do the following:
Create a class for the attached properties
Create an attached property (for example called BackstageAnimationProperty). Then in its PropertyChangedCallback get the RadRibbonBackstage element and add a handler for its Loaded event.
In the Loaded event handler, create a Storyboard with a DoubleAnimation which animates the Width of the backstage
Then you can set this attached property on the RibbonBackstage. For example:
For your convenience, I prepared a sample project which demonstrates such an implementation. Note that when you resize the RibbonView in the attached project, the backstage will not change its width automatically. This is why you will need to change the width of the backstage in its SizeChanged handler.
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