Canvas.GetLeft is NaN

I have a custom FrameworkElement which is added via code to a canvas.
Whenever I ask the canvas the position of the element via
Canvas.GetLeft(...) I get a NaN.

What is wrong?


The custom element is defined as

public class CustomRender : FrameworkElement
{
protected override void OnRender(DrawingContext drawingContext)
{
base.OnRender(drawingContext);

drawingContext.DrawRectangle(Brushes.Red, null, new Rect(0,
0, 100, 50));

FormattedText text = new FormattedText("Whatever",
CultureInfo.CurrentUICulture,
FlowDirection.LeftToRight,
new Typeface("Verdana"), 12, Brushes.Black);
drawingContext.DrawText(text, new Point(23, 23));
}
protected override Size MeasureOverride(Size availableSize)
{
return new Size(100, 50);
}
}

while the addition is done as:

{
...
cr = new CustomRender();
canvas.Children.Add(cr);
cr.MouseDown += new MouseButtonEventHandler(cr_MouseDown);
...
}


void cr_MouseDown(object sender, MouseButtonEventArgs e)
{
double left = Canvas.GetLeft(e.Source as UIElement); //gives NaN
}

Canvas.GetLeft is returning NaN (the default value for that property)
because, as far as I can tell, you never set the Canvas.Left property on
your CustomRender object. Until you give the object a Canvas.Left value
using the Canvas.SetLeft method, it will continue to return NaN.

It seems like the question you want to answer is "where did this thing end
up?" To determine the position of a Visual relative to its parent, you can
use the VisualTreeHelper.GetOffset method.

Vector offset = VisualTreeHelper.GetOffset(cr);

Thanks,

Mike Jacobs [MSFT]


<NetronProject@gmail.com> wrote in message
news:1149623142.710923.298030@g10g2000cwb.googlegroups.com...
>I have a custom FrameworkElement which is added via code to a canvas.
> Whenever I ask the canvas the position of the element via
> Canvas.GetLeft(...) I get a NaN.
>
> What is wrong?
>
>
> The custom element is defined as
>
> public class CustomRender : FrameworkElement
> {
> protected override void OnRender(DrawingContext drawingContext)
> {
> base.OnRender(drawingContext);
>
> drawingContext.DrawRectangle(Brushes.Red, null, new Rect(0,
> 0, 100, 50));
>
> FormattedText text = new FormattedText("Whatever",
> CultureInfo.CurrentUICulture,
> FlowDirection.LeftToRight,
> new Typeface("Verdana"), 12, Brushes.Black);
> drawingContext.DrawText(text, new Point(23, 23));
> }
> protected override Size MeasureOverride(Size availableSize)
> {
> return new Size(100, 50);
> }
> }
>
> while the addition is done as:
>
> {
> ...
> cr = new CustomRender();
> canvas.Children.Add(cr);
> cr.MouseDown += new MouseButtonEventHandler(cr_MouseDown);
> ...
> }
>
>
> void cr_MouseDown(object sender, MouseButtonEventArgs e)
> {
> double left = Canvas.GetLeft(e.Source as UIElement); //gives NaN
> }
>