Beginning Web Development, Silverlight, and ASP.NET AJAX

CHAPTER 16 ■ PROGRAMMING SILVERLIGHT WITH XAML AND JAVASCRIPT 397
You remove the event listener using the RemoveEventListener method on the control.
You specify the event name and the handler token in the same way as you did when
adding the event listener. Here’s an example:
txtBlock.removeEventListener("mouseLeftButtonDown", handleTxtClick);
The CaptureMouse and ReleaseMouseCapture Methods
The CaptureMouse method allows the object to receive mouse events even when the
mouse isn’t within its borders. This is typically used for dragging events, so that once you
start dragging an object, you don’t have to be within its bounds to continue dragging it.
This is released using the ReleaseMouseCapture method.
Here’s an example where they are being used in conjunction with a handler for the
MouseMove event, which will be discussed later in this chapter:
var isMouseCaptured;
function handleLoad(control, context, sender)
{
var txtBlock=control.content.findName("txt");
txtBlock.addEventListener("MouseLeftButtonDown","mouseDown");
txtBlock.addEventListener("MouseLeftButtonUp","mouseUp");
txtBlock.addEventListener("MouseMove","mouseMove");
isMouseCaptured = false;
}
function mouseDown(sender,mouseEventArgs)
{
sender.captureMouse();
isMouseCaptured = true;
}
function mouseUp(sender, mouseEventArgs)
{
sender.releaseMouse();
isMouseCaptured = false;
}
function mouseMove(sender, mouseEventArgs)
{
if(isMouseCaptured)
{
sender.setValue("Canvas.Top", mouseEventArgs.getPosition(null).x);
sender.setValue("Canvas.Left", mouseEventArgs.getPosition(null).y);
}
}