How to register touches while another finger is held down

On a WP7 device I have a canvas. When the user touches anywhere on the canvas an image is displayed at that position.

I want to add a feature where if a user touches and holds the screen with one finger and then touches the screen in another place with a different finger an image is also displayed. So basic开发者_开发技巧ally I want to be able capture and respond to the second touch in the simplest possible way. Any ideas?

Have you taken a look at the GestureService? The Pinch* events let you handle two simultanious touches.

See example.

what you need is just the GestureListener which lies in the Microsoft.Phone.Controls namespace, which can handle a couple gestures like

• Flick
• Pinch
• Drag
• Swipe
• etc.

You can use it like so

var gestureListener = GestureService.GetGestureListener(myCanvas);

//registering the Events
gestureListener.PinchStarted += new EventHandler<PinchStartedGestureEventArgs>(PinchStartedHandler);
gestureListener.PinchDelta += new EventHandler<PinchGestureEventArgs>(PinchDeltaHandler);
gestureListener.PinchCompleted += new EventHandler<PinchGestureEventArgs>(PinchCompletedHandler);

In the approriate Hanler-Methods you do your rotate- and scale- transformations.

Since you are clearly in Silverlight, this post shows you how to implement multitouch for yourself - http://mine.tuxfamily.org/?p=111

Register for touches

 Touch.FrameReported += new TouchFrameEventHandler(Touch_FrameReported);

Then handle those touches:

 void Touch_FrameReported(object sender, TouchFrameEventArgs e)
 {
        // if there are more than one finger on screen
        if (e.GetTouchPoints(myCanvas).Count == 2)
        {
            TouchPointCollection tpc = e.GetTouchPoints(myCanvas);
            // use tpc[0].Position
            // use tpc[1].Position
        }
 }

Alternatively, if you want to use ready-build Gestures, then consider using the latest Silverlight Toolkit - see this blog post for information - http://3water.wordpress.com/2011/03/09/wp7-gesture-recognition-2/