Android for Game Developers - Beginning Android Games - page 133

textView.setText("Touch and drag (one finger only)!");
textView.setOnTouchListener( this );
setContentView(textView);
}
public boolean onTouch(View v, MotionEvent event) {
builder.setLength(0);
switch (event.getAction()) {
case MotionEvent. ACTION_DOWN :
builder.append("down, ");
break ;
case MotionEvent. ACTION_MOVE :
builder.append("move, ");
break ;
case MotionEvent. ACTION_CANCEL :
builder.append("cancel", ");
break ;
case MotionEvent. ACTION_UP :
builder.append("up, ");
break ;
}
builder.append(event.getX());
builder.append(", ");
builder.append(event.getY());
String text = builder.toString();
Log.d("TouchTest", text);
textView.setText(text);
return true ;
}
}
We let our activity implement the OnTouchListener interface. We also have two members: one for
the TextView , and a StringBuilder we'll use to construct our event strings.
The onCreate() method is pretty self-explanatory. The only novelty is the call to
TextView.setOnTouchListener() , where we register our activity with the TextView so that it
receives MotionEvent s.
What's left is the onTouch() method implementation itself. We ignore the view argument, as
we know that it must be the TextView . All we are interested in is getting the touch event type,
appending a string identifying it to our StringBuilder , appending the touch coordinates, and
updating the TextView text. That's it. We also log the event to LogCat so that we can see
the order in which the events happen, as the TextView will only show the last event that we
processed (we clear the StringBuilder every time onTouch() is called).
One subtle detail in the onTouch() method is the return statement, where we return true .
Usually, we'd stick to the listener concept and return false in order not to interfere with the
event-dispatching process. If we do this in our example, we won't get any events other than
the MotionEvent.ACTION_DOWN event. So, we tell the TextView that we just consumed the event.
That behavior might differ between different View implementations. Luckily, we'll only need three
other views in the rest of this topic, and those will happily let us consume any event we want.