Sliding finger across screen activating buttons as if they were pressed

Question

In case my title wasn't clear enough, I'll explain it in detail:

Say we have a screen filled with multiple buttons (10+), and we press down on one, activating onTouch/onClick. If we now move the finger, without lifting it, I want it to activate any other button it slides over. In this particular case, I want sound to be played when you slide over a virtual piano.

I know about the onTouchListener-solution where you register every ACTION_MOVE and find some boundaries that activates new events, but that's far from optimal if you have multiple buttons and want to allow smooth sliding without delay.

I also read this thread which suggested that we combine the touchListener of the View with a gesturelistener from the activity, but once again, this does not feel at all optimal for my situation.

I have not tried combining touchlistener with gesturelistener yet, but I will go ahead and do so if someone tells me they have no other way of doing this.

Answer 1

In my opinion, the proper way of doing this is to forget about buttons, and create a custom view which draws the entire keyboard. In this view you can handle touch events the way you like. You do not even need the gesture detector, just analyze the action and coordinates of motion events, it's very easy.

I don't understand what you mean about ACTION_MOVE and delays. To minimize delay, react on ACTION_DOWN, and then on ACTION_MOVE if it hovers other keys while in down state. It can't be any faster than that. With buttons there is an important delay because the onClick() event is triggered when the user lift the finger, on ACTION_UP.

Buttons are just not meant to work as you describe. The idea is that if a user taps on a button and then move his finger away at the same time it does not trigger onClick events on other views around. This prevents bogus clicks.

Answer 2

I actually took the "easy" way out and used buttons with an onTouch-method using ACTION_DOWN and ACTION_MOVE with coordinate calculations that combined with event.getX() and event.getY() allows me to detect which button is currently hovered. It's lag free with 13 buttons.