Python kivy 小部件 position

Question

我正在 kivy 中制作足球雜耍游戲，但遇到了問題。 在我開始游戲之前，足球 position 在屏幕中間，但在比賽結束后，足球 position 在旁邊。 我怎樣才能讓它在比賽結束后足球在屏幕中間，就像我開始比賽之前一樣？ 下面是我的代碼！ 任何幫助都會得到幫助！ 謝謝你！

主文件

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()

游戲畫面.kv

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

Answer 1

嘗試更換：

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

和

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

Answer 2

導致問題的是（0，（0.5））。 為了在比賽結束后足球在屏幕中間，就像我開始比賽之前一樣，解決方案很簡單 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()