Canvas.GetTop() returning NaN

Question

I've got a Canvas with a few UIElements on. After I've moved them on the canvas by animating the top and left properties, very occasionally a subsiquent call to Canvas.GetTop results in NaN.

Am I not 'closing' the animations properly?

Here's how I'm doing the move

private void InternalMove(double durationMS, FrameworkElement fElement, Point point, EventHandler callback)
{
   _moveElement = fElement;
   _destination = point;

   Duration duration = new Duration(TimeSpan.FromMilliseconds(durationMS));

   DoubleAnimation moveLeftAnimation = new DoubleAnimation(Canvas.GetLeft(fElement), point.X, duration, FillBehavior.Stop);
   Storyboard.SetTargetProperty(moveLeftAnimation, new PropertyPath("(Canvas.Left)"));

   DoubleAnimation moveTopAnimation = new DoubleAnimation(Canvas.GetTop(fElement), point.Y, duration, FillBehavior.Stop);
   Storyboard.SetTargetProperty(moveTopAnimation, new PropertyPath("(Canvas.Top)"));

   // Create a storyboard to contain the animation.
   _moveStoryboard = new Storyboard();
   if (callback != null) _moveStoryboard.Completed += callback;

   _moveStoryboard.Completed += new EventHandler(s1_Completed);
   _moveStoryboard.Children.Add(moveLeftAnimation);
   _moveStoryboard.Children.Add(moveTopAnimation);
   _moveStoryboard.FillBehavior = FillBehavior.Stop;
   _moveStoryboard.Begin(fElement);
}

private void s1_Completed(object sender, EventArgs e)
{
    if (_moveStoryboard != null)
    {
       _moveStoryboard.BeginAnimation(Canvas.LeftProperty, null, HandoffBehavior.Compose);
       _moveStoryboard.BeginAnimation(Canvas.TopProperty, null, HandoffBehavior.Compose);
    }

    Canvas.SetLeft(_moveElement, _destination.X);
    Canvas.SetTop(_moveElement, _destination.Y);
}

thanks

PaulB · Accepted Answer · 2023-02-21T13:33:32.467

20

It seems than Canvas.GetTop(x) can return 'Nan' if the value is not explictly set (even tho I do explicitly set it I still sometimes get that result).

An alternative method I'm now using is

Vector offset = VisualTreeHelper.GetOffset(fElement);

which returns the position of fElement within it's container.

edited Feb 21 '23 at 13:33

answered Aug 25 '09 at 12:32

PaulB

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Oops accidentally hit the down arrow first ! Now back to what I intended giving a positive tick. – Jim Dec 23 '15 at 00:51
Not the "the general consensus" but just the default value of the attached property. – Clemens Feb 20 '23 at 22:30

score 1 · Answer 2 · answered Mar 23 '09 at 12:03

1

I've run into a similar situation (NaN), but in a different context. As I recall, it had something to do with how the element was positioned in the container.

Sorry I couldn't provide more help, but maybe this will provide some guidance.

answered Mar 23 '09 at 12:03

CodeMonkey1313

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score -1 · Answer 3 · answered Apr 25 '20 at 12:36

-1

Check back your xaml file in Properties Layout make sure value of left or top show only number but not mix (auto). Example: Top 123(auto), this caused Canvas.GetTop will return NaN.

answered Apr 25 '20 at 12:36

Bounpakhong phoomithep

31
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Canvas.GetTop() returning NaN

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