Get element position after transform

Question

I have a UIElement that has various transformations performed on it (scale and translate).

Is there a way to get the UIElement's position after transformation? I tried GetValue(Canvas.TopProperty) but it doesn't change from what it was loaded as.

I must be missing something obvious but not sure what. (I'm using silverlight)

Answer 1

It is a little bit unintuitive to do this, but it can be done. It is a two step process. First, what you want to use the TransformToVisual function (from MSDN):

Returns a transform object that can be used to transform coordinates from the UIElement to the specified object.

TransformToVisual will yield a GeneralTransform that will perform the transformation from any UIElement to any other UIElement (given that they both exist in the same visual tree). It sounds like what you want is the transformation from the RootVisual.

var transform = Application.RootVisual.TransformToVisual(myUiElement);

The transform object is now a general transformation that can be used to transform anything in the same way that myUiElement was transformed relative to RootVisual

The next step is to transform a point using that transformation.

var myUiElementPosition = transform.Transform(new Point(0,0));

The myUiElementPosition is now a Point that has been transformed and should be the position of the UIElement you're looking for. new Point(0,0) is used because I assume you want to have the position given relative to the top left corner of the RootVisual.