An Android Game Development Framework - Beginning Android Games - page 205

public boolean isKeyPressed( int keyCode) {
if (keyCode<0 || keyCode>127)
return false ;
return pressedKeys[keyCode];
}
The next method of our handler is the isKeyPressed() method, which implements the semantics
of Input.isKeyPressed() . First, we pass in an integer that specifies the key code (one of the
Android KeyEvent.KEYCODE_XXX constants) and returns whether that key is pressed or not. We
do this by looking up the state of the key in the pressedKey array after some range checking.
Remember, we set the elements of this array in the previous method, which gets called on the UI
thread. Since we are working with primitive types again, there's no need for synchronization.
public List<KeyEvent>getKeyEvents() {
synchronized ( this ) {
int len=keyEvents.size();
for ( int i=0; i<len; i++) {
keyEventPool.free(keyEvents.get(i));
}
keyEvents.clear();
keyEvents.addAll(keyEventsBuffer);
keyEventsBuffer.clear();
return keyEvents;
}
}
}
The last method of our handler is called getKeyEvents() , and it implements the semantics of the
Input.getKeyEvents() method. Once again, we start with a synchronized block and remember
that this method will be called from a different thread.
Next, we loop through the keyEvents array and insert all of its KeyEvent s into our Pool .
Remember, we fetch instances from the Pool in the onKey() method on the UI thread. Here, we
reinsert them into the Pool . But isn't the keyEvents list empty? Yes, but only the first time we
invoke that method. To understand why, you have to grasp the rest of the method.
After our mysterious Pool insertion loop, we clear the keyEvents list and fill it with the events in
our keyEventsBuffer list. Finally, we clear the keyEventsBuffer list and return the newly filled
keyEvents list to the caller. What is happening here?
We'll use a simple example to illustrate this. First, we'll examine what happens to the keyEvents
and the keyEventsBuffer lists, as well as to our Pool , each time a new event arrives on the UI
thread or the game fetches the events in the main thread:
UI thread: onKey() ->
keyEvents={ }, keyEventsBuffer={KeyEvent1}, pool={ }
Main thread: getKeyEvents() ->
keyEvents={KeyEvent1}, keyEventsBuffer={ }, pool { }
UI thread: onKey() ->
keyEvents={KeyEvent1}, keyEventsBuffer={KeyEvent2}, pool { }