InputHandler help ?

Newbie & Debugging Questions
#1

Hello guys, I just registered here, to ask you a question.

I’m trying to make input handler, and I’m using keys[e.getKeyCode] etc for it.

My question is, how to make isKeyPressed method, where it detects if key is pressed, but returns true just once ?

For example, I have int variable number. When I press and hold key space, it should add 1 to number, but only once, no matter how long i hold the spacebar.

I hope you can help me !

#2

Hey PixelDeBurner and welcome to JGO!

The best way to do this is to put all key codes you get from the keyPressed method into a HashSet, removing them in keyReleased.

Then it’s a matter of calling keyCodeSet.contains(…) to check if the key has been pressed.


HashSet<Integer> keyCodeSet = new HashSet<Integer>();

public void keyPressed(KeyEvent key) {
    keyCodeSet.add(key.getKeyCode());
}

public void keyReleased(KeyEvent key) {
    keyCodeSet.remove(key.getKeyCode());
}

public boolean isKeyPressed(int key) {
    return keyCodeSet.contains(key);
}
#3

How does this way effect performance, I read somewhere something about Set, that it’s a bit slower ?

#4

That doesn’t work… what it does is the same as keyDown, I want to test is keyPressed, but return true just once !

#5

So you want it to only return true once? You can add change isKeyPressed to:


public boolean isKeyPressed(int key) {
    boolean isPressed = keyCodeSet.contains(key);
    keyCodeSet.remove(key);
    return isPressed;
}
#6

Nope, doesn’t work …

#7

Depends on your operating system. The KeyDown and KeyTyped events are sometimes repeated, sometimes not. Some OSs have a pause before the repeat, others don’t. Just test it and see.

Storing the last key pressed and checking if it is still down should be enough, though.

#8

AFAIK KeyPressed and KeyReleased triggers only once (keyTyped triggers multiply times). But you could have a boolean value check whether the key has been released before it can be used again.

#9

As I said, it depends on how the OS handles the keyboard input.

Best way to find out is to simply add a System.out.println() message to the Key Listener method for each event, and see how it behaves.

In my case, on a WidowsXP machine, the KeyPressed and KeyTyped events keep repeating if I hold the key down.

#10

I managed to do it !!!

here is how:

Made boolean keyUp[keyCode]

if key is pressed, and it’s up set the keyUp to false, and return true.

the Code :

public boolean isKeyPressed(int key) {
		if (keyDown[key]) {
			if (keyUp[key]) {
				keyUp[key] = false;
				return true;
			} else
				return false;
		} else
			return false;
	}
#11

That makes no sense whatsoever. How can a key be down and up at the same time? How do you set these down and up keys?

#12

I don’t see a lot of point in an array of keys that are up. Most keys are up all the time. Makes more sense to simply have a single “keysDown” set and update it on every keyUp and keyDown event.

#13

I think his problem is actually checking when the key changes state, so a single pulse is sent regardless of the key being kept down or up.

If the validation is done against a single flag, the pulse will be sent continually once the flag is set.

Maybe have a hasChanged boolean that is set once the key changes, and reset on the next frame (would need an updateKeys method call each frame)

#14

My earlier post of resetting the key should work too.

#15

It’s like, if the key is down, but was not ( keyUp )…

I tried other things also, this one worked…

#16

It can get a bit confusing sometimes. Good thing is, if it works, you can always refine it in the future.