How to call a function from a class from another class in kivy Pong ball game

Question

I\'m practicing Kivy with the PongGame code given in the tutorial. I want to know how to call a function - serve_ball2() in the class PongGame from a newly created class - PongS

Answer 1

I emphasize that this seems unnecessary, and that PongSample itself seems like it needn't exist at all. However, to do what you asked, I believe the following should work. One thing I really don't like about this however, is that a PongSample instance is created in the kv file, without any other purpose than to serve ball2. However...

Why not define the serve_ball2 function in the PongSample class instead, and pass ball2 to it?

Example:

class PongSample(Widget):

    def serve_ball2(self, ball2, vel=(3,0)):
        print 'Serve ball 2'
        ball2.center = self.center
        ball2.velocity = vel

And in the PongGame class:

class PongGame(Widget):
    ball = ObjectProperty(None)
    ball2 = ObjectProperty(None)
    player1 = ObjectProperty(None)
    player2 = ObjectProperty(None)
    # add this
    sample = ObjectProperty(None)

Then in the kv file:

# add at the top

<PongSample>:
    size: self.size
    pos: self.pos

# add the below in appropriate places within the PongGame definition

PongGame:
    sample: pong_sample

    PongSample:
        id: pong_sample # now it's linked to 'sample' in PongGame

So now in PongGame you can call self.sample.serve_ball2(ball2) from any method.

Answer 2

To use your class add game.serve_ball2() to PongApp

class PongApp(App):
    def build(self):
        game = PongGame()
        game.serve_ball()
        game.serve_ball2()
        Clock.schedule_interval(game.update, 1.0 / 60.0)
        return game

And add self.ball2 to bounce off the paddles:

#bounce of paddles
self.player1.bounce_ball(self.ball)
self.player2.bounce_ball(self.ball)
self.player1.bounce_ball(self.ball2)
self.player2.bounce_ball(self.ball2)