kivy 小部件总是更新到父小部件的大小

Question

使用 kivy，我正在尝试创建自己的下拉菜单来解决我在使用内置 DropDown 小部件时遇到的一些问题。但是，当调整我的小部件大小以动画打开序列时，小部件大小保持不变。经过进一步调查，我意识到小部件的大小始终与父 RelativeLayout 相同，但我找不到原因。这是最低工作代码

from kivy.animation import Animation
from kivy.clock import Clock
from kivy.uix.relativelayout import RelativeLayout
from kivy.lang import Builder

import kivy.properties as props


KV = '''
#:import MaterialWidget materialwidget.MaterialWidget
<DropDown@RelativeLayout>
    _background: background
    canvas:
        Color:
            rgba: 1, 0, 0, 1
        Rectangle:
            pos: root._pos
            size: root._size
    Button:
        id: background
        size: root._size
        pos: root._pos
        on_size: print("size_changed", self.size)
'''

class DropDown(RelativeLayout):
    opened = props.BooleanProperty(False)

    anchor = props.OptionProperty("tl", options=["tr", "tl", "br", "bl"])

    _size = props.ListProperty([0, 0])
    _pos = props.ListProperty([0, 0])

    _background = props.ObjectProperty(None)

    def __init__(self, **kwargs):
        super(DropDown, self).__init__(**kwargs)

        #self.add_widget(self._background)

        trigger = Clock.create_trigger(lambda *args: self.on_pos())
        trig = Clock.create_trigger(lambda *args: self.on_size())

        self.bind(
            anchor=trigger,
            _size=trigger,
            opened=trig
        )

    def on_pos(self, *args):
        # calculate new pos
        invert_x = "r" in self.anchor
        invert_y = "t" in self.anchor

        self._pos = (
            self.pos[0] - self._size[0] if invert_x else 0,
            self.pos[1] - self._size[1] if invert_y else 0
        )

    def on_size(self, *args):
        anim = Animation(
            _size=self.size if self.opened else (0, 0),
            duration=0.5,
            transition="in_out_circ"
        )
        anim.start(self)

    def open(self, *args):
        # toggle the value of open state
        self.opened = not self.opened

Builder.load_string(KV)


if __name__ == "__main__":
    from kivy.app import runTouchApp
    from kivy.uix.button import Button
    from kivy.core.window import Window

    class Test(Button):
        def __init__(self, **kwargs):
            super(Test, self).__init__(**kwargs)
            self.size = (100, 100)
            self.size_hint = (None, None)

            self.dropdown = DropDown(pos=(200, 100), size=(400, 300))
            self.add_widget(self.dropdown)

            self.bind(on_release=lambda *args: self.dropdown.open(self))

    Window.clearcolor = (1, 1, 1, 1)
    runTouchApp(Test())

Answer 1

您可能需要在您的DropDown 上设置size_hint: None, None。如果size_hint 不是None，它将覆盖任何size 设置（包括size 属性的动画）。