Implementation

For information about the design and functionality of the MIDlet, see section Design.

To implement multipoint touch handling in the MIDlet:

1. Enable multipoint touch events on Symbian devices by setting the following attribute in the MIDlet JAD file:

   Nokia-UI-Enhancement: EnableMultiPointTouchEvents

   Multipoint touch events are enabled by default on Series 40 devices that support multipoint touch. This attribute value is therefore ignored on Series 40 devices.

2. Catch touch events by overriding selected Canvas methods. The getPointerEventId method is used to track individual multipoint touch events through the com.nokia.pointer.number system property (see the following step). Every event creates a new Point instance whose state depends on the event type.

   Note: The com.nokia.pointer.number system property is not supported on Series 40 devices, which means that the getPointerEventId always returns 0. The multipoint touch implementation used in this example therefore does not track individual multipoint touch events on Series 40 devices. While the MIDlet nevertheless draws the worm-like animation for each touch point normally, the animations are all drawn with the same color (yellow, since that is the color for touch points whose ID is 0). To track individual multipoint touch events on Series 40 devices, use the Multipoint Touch API.

       protected void pointerPressed(int x, int y)
       {
           int pointerId = this.getPointerEventId();
           this.addPoint(pointerId, new Point(x, y, Point.PRESSED));
           this.exitButtonPointerDown = this.exitButtonHitTest(x, y);
           this.inactivityCounter[pointerId] = 0;
       }
   
       protected void pointerDragged(int x, int y)
       {
           int pointerId = this.getPointerEventId();
           this.addPoint(pointerId, new Point(x, y, Point.DRAGGED));
           this.exitButtonPointerDown = this.exitButtonHitTest(x, y);
           this.inactivityCounter[pointerId] = 0;
       }
   
       protected void pointerReleased(int x, int y)
       {
           int pointerId = this.getPointerEventId();
           this.addPoint(pointerId, new Point(x, y, Point.RELEASED));
           if (this.exitButtonPointerDown && this.exitButtonHitTest(x, y))
           {
               this.inactivityTimer.cancel();
               Display.getDisplay(this.midlet).setCurrent(null);
               this.midlet.notifyDestroyed();
           }
           else
           {
               this.exitButtonPointerDown = false;
           }
           this.inactivityCounter[pointerId] = 0;
       }

3. Obtain the pointer number of the pointer that was the source of the event by calling the System.getProperty("com.nokia.pointer.number") method. This method exists only in the scope of the methods pointerPressed, pointerDragged, and pointerReleased. Outside these methods, the returned value is null.

   Note: On Series 40 devices, this method always returns 0. For more information, see the preceding step.

       private int getPointerEventId()
       {
           String idString = System.getProperty("com.nokia.pointer.number");
           int id = 0;
           if (idString != null)
           {
               id = Integer.parseInt(idString);
           }
           return id;
       }

   The currentPoints array stores the Points:

   private Point[][] currentPoints = new Point[6][25];

In conclusion, this example supports six simultaneous touches and each of them can have a maximum of 25 circles drawn on the screen to create the worm-like animation. When a point is created, it is stored to the correct index of the currentPoints array, depending on the pointer number.