Changing a Kivy Widget Text

Question

I am attempting to create a pong game using kivy. However, I am running into issues when I try to end a game after someone scores 10 points. Everything is working well except that I would like to show a Game Over text using a label. I created a label and currently the text is set to an empty string, but it should change after someone scores enough points.

I have looked through the kivy documentation and searched stackoverflow but I have not found an answer for this(or at least not one that I understand.)

If someone can point me in the right direction I would really appreciate it.

Here is my code:

.py file:

from kivy.app import App
from kivy.uix.widget import Widget
from kivy.uix.label import Label
from kivy.properties import NumericProperty, ReferenceListProperty,\
ObjectProperty
from kivy.vector import Vector
from kivy.clock import Clock


count1 = 0
count2 = 0



class PongPaddle(Widget):
    score = NumericProperty(0)

    def bounce_ball(self, ball):
        if self.collide_widget(ball):
            vx, vy = ball.velocity
            offset = (ball.center_y - self.center_y) / (self.height / 2)
            bounced = Vector(-1 * vx, vy)
            vel = bounced * 1.1
            ball.velocity = vel.x, vel.y + offset


class PongBall(Widget):
    velocity_x = NumericProperty(0)
    velocity_y = NumericProperty(0)
    velocity = ReferenceListProperty(velocity_x, velocity_y)

    def move(self):
        self.pos = Vector(*self.velocity) + self.pos


class PongGame(Widget):
    ball = ObjectProperty(None)
    player1 = ObjectProperty(None)
    player2 = ObjectProperty(None)


    def serve_ball(self, vel=(4, 0)):
        self.ball.center = self.center
        self.ball.velocity = vel

    def update(self, dt):
        global count1
        global count2

        self.ball.move()

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

        #bounce ball off bottom or top
        if (self.ball.y < self.y) or (self.ball.top > self.top):
            self.ball.velocity_y *= -1

        #went of to a side to score point?
        if self.ball.x < self.x:
            self.player1.score += 1
            count2 = count2 + 1
            self.serve_ball(vel=(4, 0))
        if self.ball.x > self.width:
            self.player2.score += 1
            self.serve_ball(vel=(-4, 0))

        if count1 or count2 >= 10:
            #
            #
            #
            #I don't know what needs to be placed here to change the third label's text


    def on_touch_move(self, touch):
        if touch.x < self.width / 3:
            self.player1.center_y = touch.y
        if touch.x > self.width - self.width / 3:
            self.player2.center_y = touch.y

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



if __name__ == '__main__':
    PongApp().run()

.kv file

#:kivy 1.0.9

<PongBall>:
    size: 50, 50
    canvas:
        Ellipse:
            pos: self.pos
            size: self.size

<PongPaddle>:
    size: 25, 200
    canvas:
        Rectangle:
            pos: self.pos
            size: self.size


<PongGame>:
    ball: pong_ball
    player1: player_left
    player2: player_right

    canvas:
        Rectangle:
            pos: self.center_x - 5, 0
            size: 10, self.height

    Label:
        font_size: 70
        center_x: root.width / 4
        top: root.top - 50
        text: str(root.player2.score)

    Label:
        font_size: 70
        center_x: root.width * 3/4
        top: root.top - 50
        text: str(root.player1.score)

    PongBall:
        id: pong_ball
        center: self.parent.center

    PongPaddle:
        id: player_left
        x: root.x
        center_y: root.center_y

    PongPaddle:
        id: player_right
        x: root.width-self.width
        center_y: root.center_y

    Label:
        id: game_over_label
        text: " "
        font_size: 100
        center_x: root.width / 2
        center_y: root.height / 2

Answer 1

You would use the same method to change the game over label that you use to change the score labels when the score changes.

If you add an ObjectProperty to PongGame in main.py:

end_label = ObjectProperty()

And in your kv file under PongGame , write:

end_label: game_over_label  # linking them up

You could add a function to PongGame class in main.py:

def check_score(self):
    scores = [self.player1.score,
              self.player2.score]
    for s in scores:
        if s == 10:
            self.end_label = "Game Over"
            return

Then in your update function, you could call this function any time the scores are incremented, for instance:

 self.player1.score += 1
 self.check_score()

and the same for self.player2.score

Answer 2

one way to find the ID inside the tree is to put a "redirector" in the root of the widget

In .kv, right under PongGame:

        gameoverlabel: game_over_label

in .py under the " if count1 or count2 >= 10:" add

        self.gameoverlabel.text = "win"

hope this is helpful