Why ActualWidth and ActualHeight start from 0,0?

Question

I want to add WPF Path to InkCanvas and use selection to select WPF Path. So, I use this code.

System.Windows.Shapes.Path path = drawCanvas.Children[i] as System.Windows.Shapes.Path;    
drawCanvas.Children.RemoveAt(i);
inkCanvas.Children.Add(path);

This is the output. I have to select WPF Path from 0,0 because Actualwidth and ActualHeight start from 0,0.

How do I select absolute WPF Path?

Thanks

Edit:

Now, I can select it absolutely by using this code.

System.Windows.Shapes.Path path = drawCanvas.Children[i] as System.Windows.Shapes.Path;
drawCanvas.Children.RemoveAt(i);
path.Margin = new Thickness(-getMinX(path), -getMinY(path), 0, 0);
containPath.Children.Add(path);
containPath.Width = getMaxX(path) - getMinX(path);
containPath.Height = getMaxY(path) - getMinY(path);
containPath.Margin = new Thickness(getMinX(path), getMinY(path), 0, 0);
inkCanvas.Children.Add(containPath);

Stereotomy

Answer 1

You can use the UIElement.UpdateLayout Method on the InkCanvas to update the FrameworkElement.ActualWidth Property and ActualHeight. See the ActualWidth link for background information on why this is needed.

Edit:

I misunderstood the question. It wasn't that ActualWidth and ActualHeight were zero but that their values were relative to (0, 0) on the InkCanvas. A pretty good solution to the problem is to wrap the Path in a Canvas and position it using Margin like this:

<Canvas Width="50" Height="50" Margin="200,200,0,0">
    <Line
        X1="0" Y1="0"
        X2="50" Y2="50"
        Stroke="Black"
        StrokeThickness="4" />
</Canvas>

which behaves like:

The disadvantage of this approach is the user has to lasso the Canvas which is a rectangle, not an arbitrary shape. Nevertheless, it's a lot better than having to lasso the object and the origin.

Helladic

I dont think UpdateLayout will do anything. – Biliary

We don't have enough code to test the theory but if UIElement.IsMeasureValid is false, there is no hope of ActualWidth and ActualHeight being correct. – Helladic

Please see my answer. In my earlier comment I meant to say that UpdateLayout will not do anything for a 'Path' – Biliary

Thanks, I can select it absolutely now. – Stereotomy

+1 - Thanks @RickSladkey, using UpdateLayout() based on your answer made ActualWidth become available in my project. Much appreciated. – Peripeteia

Answer 2

For elements that can only be defined via control points (eg Line, Path etc as against Rectangle, Ellipse etc) when you add it to an items control (which I assume the InkCanvas is since it supports selection), first a canvas is added to the panel at 0,0. The width and the Height of the canvas are determined from the maximum X and Y coordinates of the control points. After this the element is added as a child of this canvas.

You will also see that whenever you see this kind of behaviors with an element, the element wont support Layout Properties like Horizontal/Vertical alignment etc.

The only way I see around this is to find the ActualWidth and ActualHeight manually from the coordinates in the path.

Edit: This is from personal experience and not from any documentation.

Biliary

I can find ActualWidth and ActualHeight manually now. But I cannot set them to ActualWidth and ActualHeight because they are read only. – Stereotomy

ActualWidth and ActualHeight are readonly dependency properties (if memory serves right). You simply cannot and should not set it yourself. – Biliary

For selection adorners, you will have to do a lot of manual stuff to do what you want. When you add an item to an inkcanvas it will be wrapped into a container item. This container item is what is decorated by the selection adorner. Since you container contains the canvas starting at 0,0, you see the odd selection box. You need to create a derived container item which takes care of selection adorners yourself. – Biliary

Frankly, if you have just started out with WPF, this is going to look like a huge task because you will need to do a lot of sub classing and come up with your own derived InkCanvas and children etc. And the final result doesnt show much for it. :D – Biliary

The InkCanvas has two selection concepts: elements and strokes. The elements have all the problems you describe. But what if we convert the path, which appears to be a series of line segments, into strokes? Then we can let the InkCanvas do its job with the lasso. – Helladic

What you suggest is possible. Problem is except for delete, the adorner is pretty much useless in this case. Even for moving(as against resizing) you will need a custom element. My experience had been that subclassing is the only logical solution to what I believe OP wants to do after selection. – Biliary