How do you calculate the offset to the client area in WPF?

Question

I want to position a modal dialog (progress window) at the top right corner of the parent window client area.

This code will put it in the corner of the non-client area, but how do I calculate the offset to the client area?

this.Owner=owner;
this.Left=owner.Left+owner.ActualWidth-Width;
this.Top=owner.Top;

Edit:

I found this 'solution' that works for normal windows:

this.Left=owner.Left+owner.ActualWidth-Width-SystemParameters.ResizeFrameVerticalBorderWidth;
this.Top=owner.Top+SystemParameters.ResizeFrameHorizontalBorderHeight+SystemParameters.WindowCaptionHeight;

This would however fail for windows that have customized borders.

EDIT:

The code should work regardless of the systems DPI setting (e.g. 120 instead of 96).

Answer 1

As long as your window content is a subclass of UIElement (which is normally the case), you can simply check the area covered by the Content:

Matrix scaling = PresentationSource.FromVisual(windowContent)
                   .CompositionTarget.TransformFromDevice;

UIElement windowContent = owner.Content as UIElement;

Point upperRightRelativeToContent = new Point(
  windowContent.RenderSize.Width + owner.Margin.Right,
  -owner.Margin.Top);

Point upperRightRelativeToScreen =
  windowContent.PointToScreen(upperRightRelativeToContent);

Point upperRightScaled =
  scaling.Transform(upperRightRelativeToScreen);

this.Owner = owner;
this.Left = upperRightScaled.X - this.Width;
this.Top = upperRightScaled.Y;

If you have a strange situation where you want this to work for arbitrary Window.Content, you'll have to search the window's visual tree using VisualTreeHelper.GetChildCount() and VisualTreeHelper.GetChild() until you come to a ContentPresenter whose Content property matches that of the Window, and use its first visual child as "windowContent" in the above code.