mouse leaves object while moving

11-08-2009 7:19 AM |

I made my object moving when my mouse downs on it, but when I move the mouse faster it leaves the object and I have to go back to pick it up. Why is that? Here' s the code:

XAML:

1    <UserControl
2    	xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
3    	xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
4    	x:Class="HideShowTest.MainPage"
5    	Width="640" Height="480">
6    
7    	<Canvas x:Name="LayoutRoot" Background="#FF636363">
8    		<Ellipse Fill="#FF4BC18E" Height="87" Width="87" Canvas.Left="88" Canvas.Top="300" MouseLeftButtonDown="down" MouseMove="move"/>
9    	</Canvas>
10   </UserControl>

C#:

1    bool isMouseCaptured = false;
2    double mouseVerticalPosition;
3    double mouseHorizontalPosition;
4    
5    ...
6    
7    private void down(object sender, MouseButtonEventArgs e)
8    {
9        FrameworkElement item = sender as FrameworkElement;
10   
11       if (isMouseCaptured == false)
12       {
13           mouseVerticalPosition = e.GetPosition(null).Y;
14           mouseHorizontalPosition = e.GetPosition(null).X;
15           isMouseCaptured = true;
16           item.CaptureMouse();
17       }
18       else
19       {
20           isMouseCaptured = false;
21       }
22    }
23   
24   private void move(object sender, MouseEventArgs e)
25   {
26       FrameworkElement item = sender as FrameworkElement;
27   
28       if (isMouseCaptured == true)
29       {
30           double deltaV = e.GetPosition(null).Y - mouseVerticalPosition;
31           double deltaH = e.GetPosition(null).X - mouseHorizontalPosition;
32           double newTop = deltaV + (double)item.GetValue(Canvas.TopProperty);
33           double newLeft = deltaH + (double)item.GetValue(Canvas.LeftProperty);
34   
35           item.SetValue(Canvas.TopProperty, newTop);
36           item.SetValue(Canvas.LeftProperty, newLeft);
37   
38           mouseVerticalPosition = e.GetPosition(null).Y;
39           mouseHorizontalPosition = e.GetPosition(null).X;
40       }
41   }

Thanks!

Re: mouse leaves object while moving

11-08-2009 12:29 PM |

I can see you're using CaptureMouse but I cannot see you releasing it anywhere. CaptureMouse also returns a bool value if it fails - you should check if the mouse is really captured.

Another thing: your application is not full screen, only 640x480, so if you move mouse quickly, you may move the mouse pointer outside the application area. In this case it will no longer receive the mouse move event and the dragged element will drop at the edge. You should use the LostMouseCapture event to detect this situation.

Re: mouse leaves object while moving

11-08-2009 2:31 PM |

Did you add a MouseLeave and MouseLeftButton up events to release the mouse controls?

XAML:  

<Canvas x:Name="LayoutRoot" Background="#FF636363">
    <Ellipse Fill="#FF4BC18E" Height="87" Width="87" Canvas.Left="88" Canvas.Top="300" MouseLeftButtonDown="down" MouseLeftButtonUp="up" MouseMove="move" MouseLeave="leave"/>
</Canvas>

C#:

private void up(object sender, MouseButtonEventArgs e)
{
    FrameworkElement item = sender as FrameworkElement;
    item.ReleaseMouseCapture();

    isMouseCaptured = false;
}

private void leave(object sender, MouseEventArgs e)
{
    FrameworkElement item = sender as FrameworkElement;
    item.ReleaseMouseCapture();

    isMouseCaptured = false;
}

Re: mouse leaves object while moving

11-09-2009 1:49 AM |

But I want to release the object when I down again, not when up.