使用LibGDX按空格键时如何射击子弹？

Question

I did it as follows:

...
if (Gdx.input.isKeyPressed(Keys.SPACE)) {
   shoot();
}
...

The problem is that if I keep pressing SPACE many bullets are created. What I want is that the bullet is shot only when I press SPACE but not while I'm pressing the key.

Answer 1

Libgdx InputProcessor interface has methods to receive keyDown and keyUp events. This is probably what you should be using.

Answer 2

Took a look at the documentation for the library, and it doesn't seem to expose any other way of getting key presses (particularly key down/release). In such a case you can keep track of keep changes yourself with a spaceAlreadyPressed variable that persists between frames.

...
boolean spaceIsPressed = Gdx.input.isKeyPressed(Keys.SPACE);
if (spaceIsPressed && !spaceAlreadyPressed) {
   shoot();
}
...
spaceAlreadyPressed = spaceIsPressed;

It may be safer to use a spaceIsPressed variable in case the input state changes unexpectedly.

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Alternatively, if you want to make it shorter, you can use logical laws to reduce to the following, where canShoot also persists between frames and has an initial value of false .

...
canShoot = !canShoot && Gdx.input.isKeyPressed(Keys.SPACE);
if (canShoot) {
   shoot();
}
...