Resize a rectangle element on pinch(gesture) - windows-phone-7

Question

I am trying to crop an image. Inorder to select the crop area I am using an rectangle element.
The initial width and height of the rectangle are set to 100 respectively. On pinch the size of the rectangle will be increased. How can i obtain the size of this rectangle, which is enlarged?
The code I am using is as follows:
private void GestureListener_PinchDelta(object sender, PinchGestureEventArgs e)
{
ImageTransformation.ScaleX = _initialScale * e.DistanceRatio;
ImageTransformation.ScaleY = ImageTransformation.ScaleX;
cropRectangle.Width = cropRectangle.Width + e.DistanceRatio;
cropRectangle.Height = cropRectangle.Height + e.DistanceRatio;
}
I am unable to obtain the size of the enlarged rectangle

Answer 1

RenderTransforms won't change Width & Height of your Control because it affects only the rendering. Not sure there is a better way but you can simply calculate the render size by using the original size and the scale factor.
Here is a very basic example
xaml
<Canvas x:Name="cnv" Grid.Row="1">
<Rectangle Canvas.Top="150" Canvas.Left="150"
Width="200" Height="200" x:Name="myrect"
Fill="AliceBlue"
ManipulationStarted="myrect_ManipulationStarted"
ManipulationDelta="myrect_ManipulationDelta"
ManipulationCompleted="myrect_ManipulationCompleted">
</Rectangle>
</Canvas>
code
public MainPage()
{
InitializeComponent();
transformGroup = new TransformGroup();
translation = new TranslateTransform();
scale = new ScaleTransform();
transformGroup.Children.Add(scale);
transformGroup.Children.Add(translation);
myrect.RenderTransform = transformGroup;
}
private TransformGroup transformGroup;
private TranslateTransform translation;
private ScaleTransform scale;
private void myrect_ManipulationStarted(object sender, ManipulationStartedEventArgs e)
{
//change the color of the Rectangle to a half transparent Red
myrect.Fill = new SolidColorBrush(Color.FromArgb(127, 255, 0, 0));
}
private void myrect_ManipulationDelta(object sender, ManipulationDeltaEventArgs e)
{
translation.X += e.DeltaManipulation.Translation.X;
translation.Y += e.DeltaManipulation.Translation.Y;
//Scale the Rectangle
if (e.DeltaManipulation.Scale.X != 0)
scale.ScaleX *= e.DeltaManipulation.Scale.X;
if (e.DeltaManipulation.Scale.Y != 0)
scale.ScaleY *= e.DeltaManipulation.Scale.Y;
}
private void myrect_ManipulationCompleted(object sender, ManipulationCompletedEventArgs e)
{
myrect.Fill = new SolidColorBrush(Color.FromArgb(255, 255, 0, 0));
Debug.WriteLine(myrect.Width * scale.ScaleX);
Debug.WriteLine(myrect.Height * scale.ScaleY);
}