Change the parent of a WPF element after a rotation (setting new coordinates issue)

Question

I need to change the parent of elements. (for group/ungroup shapes) But I cant set the new position for an element if it has a rotation.

I saw this ,this , this and this pages and many other ways, but none worked correctly.

Please see my sample project and the following image:

The parent of Rect1 is ChildCanvas1 and The parent of Rect2 is ChildCanvas2, I want to move the Rect1 and Rect2 to the MainCanvas. (and remove the ChildCanvas and ChildCanvas2)

I don't have any problem to do that for the Rect1 because it has not any rotation. But the Rect2 has a rotation (-20 degree) and I cant set the new coordinates for it correctly.

Please see this image:

How to change the parent of an element after a rotation and setting new coordinates correctly?

UPDATE:

Note I need a general way (for the group/ungroup elements in a big app that each element (maybe) has TranslateTransform and SkewTransform and RotateTransform and ScaleTransform)

XAML:

<Canvas x:Name="MainCanvas">
    <Canvas x:Name="ChildCanvas1" Width="500" Height="250" Background="Bisque" Canvas.Top="54">
        <Rectangle x:Name="Rect1" Width="200" Height="100" Fill="Red" Canvas.Left="150" Canvas.Top="100"/>
    </Canvas>

    <Canvas Name="ChildCanvas2" Width="500" Height="250" Background="Bisque" Canvas.Left="516" Canvas.Top="54">
        <Rectangle Name="Rect2" Width="200" Height="100" Fill="Red" Canvas.Left="150" Canvas.Top="100">
              <Rectangle.RenderTransform>
                <TransformGroup>
                    <SkewTransform AngleX="-40"/>
                <RotateTransform Angle="-20"/>
                </TransformGroup>
            </Rectangle.RenderTransform>
        </Rectangle>
    </Canvas>
    <Button Name="btn1" Click="btn1_Click" Content="Move Rect1 to MainCanvas and Remove ChildCanvas1" Width="356" Height="30" Canvas.Left="59" Canvas.Top="310"/>
    <Button Name="btn2"  Click="btn2_Click" Content="Move Rect2 to MainCanvas and Remove ChildCanvas2" Width="350" Height="30" Canvas.Left="590" Canvas.Top="310"/>

C# code :

GeneralTransform transform = Rect2.TransformToVisual(MainCanvas);
Rect rect = transform.TransformBounds(new Rect(0, 0, Rect2.Width, Rect2.Height));
double ChildCanvas2Left = Canvas.GetLeft(ChildCanvas2);
double ChildCanvas2Top = Canvas.GetLeft(ChildCanvas2);
ChildCanvas2.Children.Remove(Rect2);
MainCanvas.Children.Add(Rect2);
Canvas.SetLeft(Rect2, rect.Left);
Canvas.SetTop(Rect2, rect.Top);
MainCanvas.Children.Remove(ChildCanvas2);

OK. Check my answer. Also please update your question and post the XAML and c# code instead of attachment to your project so that it will be reproducible to future visitors. — Salah Akbari
– Salah Akbari, Commented Jun 27, 2016 at 13:08

Salah Akbari · Accepted Answer · 2016-06-27 13:40:16Z

You need to recalculate the Rect2 after moving the Rect2 to the MainCanvas. Like this:

Canvas.SetTop(Rect2, Canvas.GetTop(Rect2) + Canvas.GetTop(ChildCanvas2));

The complete code:

private void btn2_Click(object sender, RoutedEventArgs e)
{       
    GeneralTransform transform = Rect2.TransformToVisual(MainCanvas);
    Rect rect = transform.TransformBounds(new Rect(0, 0, Rect2.Width, Rect2.Height));
    ChildCanvas2.Children.Remove(Rect2);
    MainCanvas.Children.Remove(ChildCanvas2);
    Canvas.SetLeft(Rect2, rect.Left);
    Canvas.SetTop(Rect2, Canvas.GetTop(Rect2) + Canvas.GetTop(ChildCanvas2));
    MainCanvas.Children.Add(Rect2);      
}

However Rect2.TransformToVisual and transform.TransformBounds are not necessary in your case and you can do it more cleaner and easier without them and get same result. Like this:

ChildCanvas2.Children.Remove(Rect2);
MainCanvas.Children.Remove(ChildCanvas2);
Canvas.SetLeft(Rect2, Canvas.GetLeft(Rect2) + Canvas.GetLeft(ChildCanvas2));
Canvas.SetTop(Rect2, Canvas.GetTop(Rect2) + Canvas.GetTop(ChildCanvas2));
MainCanvas.Children.Add(Rect2);

EDIT: A general way:

ChildCanvas2.Children.Remove(Rect2);
MainCanvas.Children.Remove(ChildCanvas2);
Canvas.SetLeft(Rect2, Canvas.GetLeft(Rect2) + Canvas.GetLeft(ChildCanvas2));
Canvas.SetTop(Rect2, Canvas.GetTop(Rect2) + Canvas.GetTop(ChildCanvas2));
Canvas.SetRight(Rect2, Canvas.GetRight(Rect2) + Canvas.GetRight(ChildCanvas2));
Canvas.SetBottom(Rect2, Canvas.GetBottom(Rect2) + Canvas.GetBottom(ChildCanvas2));
MainCanvas.Children.Add(Rect2);

Paviel Kraskoŭski · Accepted Answer · 2016-06-25 15:35:47Z

2

I have changed RenderTransform to LayoutTransform of Rect2:

<Rectangle Name="Rect2" Width="200" Height="100" Fill="Red" Canvas.Left="150" Canvas.Top="100">
       <Rectangle.LayoutTransform>
           <RotateTransform Angle="-20"/>
       </Rectangle.LayoutTransform>
</Rectangle>

Now Rect2 looks like below:

When I press the second button I see this result:

So, Rect2 stays at the original position.

answered Jun 25, 2016 at 15:35

Paviel Kraskoŭski

1,4299 silver badges16 bronze badges

1 Comment

Maria Over a year ago

Thanks for your reply, but I need to do it using RenderTransform .(not LayoutTransform)

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