Question

I have a selfcreated usercontrol that inherits from canvas.
Now it is nessesary that this canvas object has always a ratio between width and height.
How is this possible?
I tried this one but it does not work:

        private void Canvas_SizeChanged(object sender, SizeChangedEventArgs e)
    {

        Vector vec = VisualTreeHelper.GetOffset(this);
        if(e.WidthChanged)
            Arrange(new Rect(vec.X, vec.Y, ActualWidth, Image.Height / Image.Width * this.ActualWidth));
        else if(e.HeightChanged)
            Arrange(new Rect(vec.X, vec.Y, Image.Width / Image.Height * this.ActualHeight, ActualHeight));

    }

Now i would like to ask if you have any ideas. The ratio is Image.Height/Image.Width (Image is the background image of the canvas object)

Answer 1

You could override ArrangeOverride:

protected override Size ArrangeOverride(Size arrangeSize)
{
    Size size = base.ArrangeOverride(arrangeSize);
    double aspectRatio = ...

    return new Size(size.Width, size.Width / aspectRatio);

    // or, if Height determines the final size
    // return new Size(size.Height * aspectRatio, size.Height);
}

And you have to make sure that the Canvas’ parent does not set its Width or Height at the same time.

You could for example put it inside another Canvas and set either your Canvas’ Width or Height explicitely. Or you put it in a Grid and set proper values for HorizontalAlignment and VerticalAlignment.