Multiple taps create index out of bounds exception - crash

Question

I am adapting Mario Zechner's Beginning Android Games framework to create a toddler color learning app. In the final phases of testing I have found that if the user presses and releases two different buttons at the same time (such as the 'settings' and 'home' buttons in the screenshot below) the "Colors! has stopped." notification appears.
Zechner's framework provides the handling of inputs in the form of a list which then processes each individually. I believe the issue resides in the #Override update area of code:
#Override
public void update(float deltaTime) {
world.timer = world.timer + deltaTime;
List<TouchEvent> touchEvents = game.getInput().getTouchEvents();
int len = touchEvents.size();
for (int i = 0; i < len; i++) {
TouchEvent event = touchEvents.get(i);
if (event.type == TouchEvent.TOUCH_UP) {
// This is where the guts of my app are
}
}
}
The following is from LogCat showing the exception (I have noticed that the "Invalid index" will be different depending on how many touches are used but the size is alway 0):
04-24 19:27:55.239: E/AndroidRuntime(28002): FATAL EXCEPTION: Thread-555
04-24 19:27:55.239: E/AndroidRuntime(28002): java.lang.IndexOutOfBoundsException: Invalid index 1, size is 0
04-24 19:27:55.239: E/AndroidRuntime(28002): at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:251)
04-24 19:27:55.239: E/AndroidRuntime(28002): at java.util.ArrayList.get(ArrayList.java:304)
04-24 19:27:55.239: E/AndroidRuntime(28002): at com.lilyandrosieshow.colors.GameScreen.update(GameScreen.java:153)
04-24 19:27:55.239: E/AndroidRuntime(28002): at com.badlogic.androidgames.framework.impl.AndroidFastRenderView.run(AndroidFastRenderView.java:42)
04-24 19:27:55.239: E/AndroidRuntime(28002): at java.lang.Thread.run(Thread.java:856)
04-24 19:28:59.301: D/dalvikvm(28002): GC_CONCURRENT freed 482K, 4% free 15473K/16071K, paused 2ms+2ms
04-24 19:32:55.262: I/Process(28002): Sending signal. PID: 28002 SIG: 9
04-24 19:32:55.262: E/AndroidRuntime(28002): Handle UnCaght exceptions. KILLING PID: 28002
I have tried to add
if (len != 0)
before the for loop but received the same results
Thank you for any and all assistance!

Answer 1

The "settings" and "home" buttons lead to another Screen implementation, with a call such as game.setScreen(new HomeScreen()). Inside that method, the Screen argument is updated with a delta-time of zero. If the argument Screen's update method also iterates through touch events by fetching them from the events of the game's UserInput instance, the current events list is no longer the same as the one being iterated over in the old Screen. The fix is to return immediately from any call to setScreen(). No need to continue touch processing.
#Override
public void update(float deltaTime) {
world.timer = world.timer + deltaTime;
List<TouchEvent> touchEvents = game.getInput().getTouchEvents();
int len = touchEvents.size();
for (int i = 0; i < len; i++) {
TouchEvent event = touchEvents.get(i);
if (event.type == TouchEvent.TOUCH_UP) {
if (touchingHomeButton(event)) {
game.setScreen(new HomeScreen());
return; // return immediately
}
}
}