Python kivy 小部件位置

Question

我正在用 kivy 制作足球杂耍游戏，但遇到了问题。在我开始游戏之前，足球的位置在屏幕中间，但在比赛结束后，足球的位置就在一边。我怎样才能让它在比赛结束后足球在屏幕中间，就像我开始比赛之前一样？下面是我的代码！任何帮助都会得到帮助！谢谢！

main.py

from kivy.app import App
from kivy.uix.screenmanager import Screen
from kivy.uix.image import Image
from kivy.core.audio import SoundLoader
from kivy.clock import Clock
from kivy.properties import NumericProperty
from kivy.vector import Vector


class HomeScreen(Screen):
    pass

    def play_sound(self):
        sound = SoundLoader.load('button press sound.wav.')
        if sound:
            sound.play()


sound = SoundLoader.load('Crowd sound effect.wav')
sound.loop = True
sound.play()


class GameScreen(Screen):
    pass

    def play_sound(self):
        sound = SoundLoader.load('button press sound.wav.')
        if sound:
            sound.play()


class Ball(Image):
    velocity_x = NumericProperty(0)
    velocity = NumericProperty(0)


    def on_touch_down(self, touch):
        if Vector(self.center).distance(touch.pos) <= 33:
            label = App.get_running_app().root.get_screen('game_screen').ids.score
            label.text = str(int(label.text) + 1)
            sound = SoundLoader.load('Soccer ball sound.wav')
            sound.play()
            self.source = "icons/ball.png"
            self.velocity = 300
            if self.center[0] + 3 < touch.pos[0]:  # click on right side
                self.velocity_x = -80
            elif self.center[0] - 3 > touch.pos[0]:  # click on left side
                self.velocity_x = +80
            else:  # click center
                self.velocity_x = 0
        return super().on_touch_down(touch)


    def on_touch_up(self, touch):
        if Vector(self.center).distance(touch.pos) <= 33:
            self.source = "icons/ball.png"
        return super().on_touch_up(touch)


class MainApp(App):
    GRAVITY = 300


    def move_ball(self, time_passed):
        ball = self.root.ids.game_screen.ids.ball
        ball.y = ball.y + ball.velocity * time_passed
        ball.x = ball.x + ball.velocity_x * time_passed
        ball.velocity = ball.velocity - self.GRAVITY * time_passed
        self.check_collision()

    def check_collision(self):
        ball = self.root.ids.game_screen.ids.ball
        if ball.top < 96:
            self.root.ids.game_screen.ids.score.text = "0"
            self.game_over()


    def game_over(self):
        self.root.ids.game_screen.ids.ball.pos = (0, (0.5) )
        print("game over")
        self.frames.cancel()
        self.root.ids.game_screen.ids.start_button.disabled = False
        self.root.ids.game_screen.ids.start_button.opacity = 1
        self.root.ids.game_screen.ids.over.opacity = 1


    def next_frame(self, time_passed):
        self.move_ball(time_passed)


    def start_game(self):
        #Clock.schedule_interval(self.move_ball, 1/60.)
        self.root.ids.game_screen.ids.ball.velocity = 275
        self.frames = Clock.schedule_interval(self.next_frame, 1/60.)
        self.root.ids.game_screen.ids.score.text = "0"
        self.root.ids.game_screen.ids.over.opacity = 0
        self.root.ids.game_screen.ids.ball.velocity_x = 0

    def change_screen(self, screen_name):
        self.root.current = screen_name



MainApp().run()

gamescreen.kv

    Ball:
        source: "icons/ball.png"
        size_hint: None, None
        size: 525, 525
        center_x: root.width / 2
        id: ball

Answer 1

尝试替换：

    self.root.ids.game_screen.ids.ball.pos = (0, (0.5) )

与

    self.root.ids.game_screen.ids.ball.center = self.root.center

Answer 2

导致问题的原因是 (0, (0.5))。为了在比赛结束后足球位于屏幕中间，就像我开始比赛之前一样，解决方案很简单，就是 self.root.center

after the game is over the soccer ball is in the middle of the screen, like how it was before I started the game

from kivy.app import App
from kivy.uix.screenmanager import Screen
from kivy.uix.image import Image
from kivy.core.audio import SoundLoader
from kivy.clock import Clock
from kivy.properties import NumericProperty
from kivy.vector import Vector


class HomeScreen(Screen):
    pass

    def play_sound(self):
        sound = SoundLoader.load('button press sound.wav.')
        if sound:
            sound.play()


sound = SoundLoader.load('Crowd sound effect.wav')
sound.loop = True
sound.play()


class GameScreen(Screen):
    pass

    def play_sound(self):
        sound = SoundLoader.load('button press sound.wav.')
        if sound:
            sound.play()


class Ball(Image):
    velocity_x = NumericProperty(0)
    velocity = NumericProperty(0)


    def on_touch_down(self, touch):
        if Vector(self.center).distance(touch.pos) <= 33:
            label = App.get_running_app().root.get_screen('game_screen').ids.score
            label.text = str(int(label.text) + 1)
            sound = SoundLoader.load('Soccer ball sound.wav')
            sound.play()
            self.source = "icons/ball.png"
            self.velocity = 300
            if self.center[0] + 3 < touch.pos[0]:  # click on right side
                self.velocity_x = -80
            elif self.center[0] - 3 > touch.pos[0]:  # click on left side
                self.velocity_x = +80
            else:  # click center
                self.velocity_x = 0
        return super().on_touch_down(touch)


    def on_touch_up(self, touch):
        if Vector(self.center).distance(touch.pos) <= 33:
            self.source = "icons/ball.png"
        return super().on_touch_up(touch)


class MainApp(App):
    GRAVITY = 300


    def move_ball(self, time_passed):
        ball = self.root.ids.game_screen.ids.ball
        ball.y = ball.y + ball.velocity * time_passed
        ball.x = ball.x + ball.velocity_x * time_passed
        ball.velocity = ball.velocity - self.GRAVITY * time_passed
        self.check_collision()

    def check_collision(self):
        ball = self.root.ids.game_screen.ids.ball
        if ball.top < 96:
            self.root.ids.game_screen.ids.score.text = "0"
            self.game_over()


    def game_over(self):
        self.root.ids.game_screen.ids.ball.center = self.root.center
        print("game over")
        self.frames.cancel()
        self.root.ids.game_screen.ids.start_button.disabled = False
        self.root.ids.game_screen.ids.start_button.opacity = 1
        self.root.ids.game_screen.ids.over.opacity = 1


    def next_frame(self, time_passed):
        self.move_ball(time_passed)


    def start_game(self):
        #Clock.schedule_interval(self.move_ball, 1/60.)
        self.root.ids.game_screen.ids.ball.velocity = 275
        self.frames = Clock.schedule_interval(self.next_frame, 1/60.)
        self.root.ids.game_screen.ids.score.text = "0"
        self.root.ids.game_screen.ids.over.opacity = 0
        self.root.ids.game_screen.ids.ball.velocity_x = 0

    def change_screen(self, screen_name):
        self.root.current = screen_name



MainApp().run()