Two element hit in canvas - wpf

Question

I have a bomb(element) in the canvas that is moving with doublanimation(vertical only) and I want to see if it hits an airplane(also an element on the canvas).
I wrote this code:
private bool HitCheck()
{
AirPlaneRect.Location = airplane.PointToScreen(new Point(Canvas.GetLeft(airplane), Canvas.GetTop(airplane)));
Rect BombPos = new Rect(bombPoint.X, Canvas.GetTop(this),this.bombImage.Height, this.bombImage.Width);
if (BombPos.IntersectsWith(AirPlaneRect))
{
return true;
}
return false;
}
but for some reason the bomb location is always the starting one.
I'm using a timer that call this method every half a second.

Answer 1

Instead of using a Timer to check periodic if they intersects, it is more accurate to check it when the DoubleAnimation is changed. When that happens, CurrentTimeInvalidated is raised.
I created a little sample to demonstrate what I mean. Here is the XAML:
<Canvas>
<!--be shure to assign Top and Left of all objects-->
<Rectangle Canvas.Left="0" Canvas.Top="0" Name="bomb"
Width="20" Height="100" Fill="gray"/>
<Rectangle Canvas.Left="0" Canvas.Top="200" Name="airPlane"
Width="300" Height="50" Fill="lightblue"/>
<Canvas.Triggers>
<!--Run the animation at startup-->
<EventTrigger RoutedEvent="Loaded">
<BeginStoryboard >
<Storyboard >
<DoubleAnimation Name="doubleAnimation"
Storyboard.TargetName="bomb"
Storyboard.TargetProperty="(Canvas.Top)"
From="0" To="400" Duration="0:0:5"
CurrentTimeInvalidated="CurrentTimeInvalidated"/>
</Storyboard>
</BeginStoryboard>
</EventTrigger>
</Canvas.Triggers>
</Canvas>
And the code behind:
private void CurrentTimeInvalidated(object sender, EventArgs e)
{
if (HitTest(airPlane, bomb))
{
MessageBox.Show("Hit!");
//unregister the event handler to avoid to see the messagebox more than once
doubleAnimation.CurrentTimeInvalidated -= CurrentTimeInvalidated;
}
}
static bool HitTest(FrameworkElement airPlane, FrameworkElement bomb)
{
var r1 = new Rect(Canvas.GetLeft(airPlane), Canvas.GetTop(airPlane), airPlane.ActualWidth, airPlane.ActualHeight);
var r2 = new Rect(Canvas.GetLeft(bomb), Canvas.GetTop(bomb), bomb.ActualWidth, bomb.ActualHeight);
return r1.IntersectsWith(r2);
}
If you do it similar to me, it should work. Or is your code structure significant different to my?