如何在 Kivy 中更改小部件颜色

Question

我正在尝试学习用于 Python GUI 编程的 Kivy 包的基础知识。我已经完成了 Pong 教程 (here) 并想通过改变乒乓球每次撞到墙上的颜色来测试我的理解力。它不起作用 - 每次球撞到墙上时，我都会收到一个错误，说没有颜色属性。我做错了什么？

main.py

from kivy.app import App
from kivy.uix.widget import Widget
from kivy.properties import  NumericProperty, ReferenceListProperty, ObjectProperty
from kivy.vector import Vector
from kivy.clock import Clock
from kivy.graphics import Color
from random import randint

class PongBall(Widget):
    vel_x = NumericProperty(0)
    vel_y = NumericProperty(0)
    vel = ReferenceListProperty(vel_x,vel_y)

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

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

    def serve_ball(self):
        self.ball.center = self.center
        self.ball.vel = Vector(4,0).rotate(randint(0,360))

    def update(self, dt):
        self.ball.move()

        if(self.ball.y < 0) or (self.ball.top > self.height):
            self.ball.vel_y *= -1
            self.ball.Color(1,0,0)

        if(self.ball.x < 0) or (self.ball.right > self.width):
            self.ball.vel_x *= -1
            self.ball.Color(0,1,0)


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 文件：

#:kivy 1.0.9

<PongBall>:
    size: 50, 50
    canvas:
        Ellipse:
            pos: self.pos
            size: self.size
        Color:
            rgba: 1, 1, 0, 0

<PongGame>:
    ball: pong_ball

    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: "0"

    Label:
        font_size: 70
        center_x: root.width * 3 / 4
        top: root.top - 50
        text: "0"

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

Answer 1

您必须执行以下操作：

• 创建一个 ListProperty 以获取颜色信息并在 .kv 中进行绑定。

• 颜色指令必须在椭圆指令之前：

class PongBall(Widget):
    vel_x = NumericProperty(0)
    vel_y = NumericProperty(0)
    vel = ReferenceListProperty(vel_x,vel_y)
    color = ListProperty((1, 1, 1, 1)) # <---

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

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

    def serve_ball(self):
        self.ball.center = self.center
        self.ball.vel = Vector(4,0).rotate(randint(0,360))

    def update(self, dt):
        self.ball.move()

        if(self.ball.y < 0) or (self.ball.top > self.height):
            self.ball.vel_y *= -1
            self.ball.color = (1, 0, 0, 1) # <---

        if(self.ball.x < 0) or (self.ball.right > self.width):
            self.ball.vel_x *= -1
            self.ball.color = (0, 1, 0, 1) # <---
# ...

<PongBall>:
    size: 50, 50
    canvas:
        Color:
            rgba: self.color # <---
        Ellipse:
            pos: self.pos
            size: self.size
# ...