如何在Kivy中制作重复的旋转动画？

Question

我想制作一个动画小部件，该小部件将旋转加载微调器图像。我看了Animation上课，看来它可以胜任。但是我找不到一种方法可以持续不断地沿单个方向旋转小部件

这是我的代码：

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.image import Image
from kivy.graphics import Rotate
from kivy.animation import Animation
from kivy.properties import NumericProperty

Builder.load_string('''                                                                                                                                        
<Loading>:                                                                                                                                                 
    canvas.before:                                                                                                                                             
        PushMatrix                                                                                                                                             
        Rotate:                                                                                                                                                
            angle: self.angle                                                                                                                                  
            axis: (0, 0, 1)                                                                                                                                    
            origin: self.center                                                                                                                                
    canvas.after:                                                                                                                                              
        PopMatrix                                                                                                                                              
''')

class Loading(Image):
    angle = NumericProperty(0)
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        anim = Animation(angle = 360)
        anim += Animation(angle = -360)
        anim.repeat = True
        anim.start(self)


class TestApp(App):
    def build(self):
        return Loading()

TestApp().run()

启动它时，您会看到该小部件沿一个方向旋转360度，然后旋转。我该如何构建动画序列，以使角度每360度旋转一次不断增加或减少到0？

Answer 1

您可以在on_angle方法内部将角度设置为0 。这是一个稍作修改的版本：

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.floatlayout import FloatLayout
from kivy.animation import Animation
from kivy.properties import NumericProperty

Builder.load_string('''                               
<Loading>:
    canvas.before:
        PushMatrix
        Rotate:
            angle: root.angle
            axis: 0, 0, 1
            origin: root.center
    canvas.after:
        PopMatrix


    Image:
        size_hint: None, None
        size: 100, 100
        pos_hint: {'center_x': 0.5, 'center_y': 0.5}
''')

class Loading(FloatLayout):
    angle = NumericProperty(0)
    def __init__(self, **kwargs):
        super(Loading, self).__init__(**kwargs)
        anim = Animation(angle = 360, duration=2) 
        anim += Animation(angle = 360, duration=2)
        anim.repeat = True
        anim.start(self)

    def on_angle(self, item, angle):
        if angle == 360:
            item.angle = 0


class TestApp(App):
    def build(self):
        return Loading()

TestApp().run()