Activities receive notifications of touch events by registering an onTouchListener event listener and implementing the onTouch() callback method which, in turn, is passed a MotionEvent object when called by the Android runtime. This object contains information about the touch such as the type of touch event, the coordinates of the touch and a count of the number of touches currently in contact with the view.
When multiple touches are involved, each point of contact is referred to as a pointer with each assigned an index and an ID. While the index of a touch can change from one event to another, the ID will remain unchanged until the touch ends.
This chapter has worked through the creation of an example Android application designed to display the coordinates and action type of up to two simultaneous touches on a device display.
Having covered touches in general, the next chapter (entitled “Detecting Common Gestures using the Android Gesture Detector Class...
