如何在 Kivy 的画布中引用孩子的 id?

问题描述

当我尝试将 id 分配给画布时，我收到错误 Invalid data after declaration，但我看不到任何其他引用该 id 的方式(例如 e1).如何在我的 Python 代码中引用 e1?

I get the error Invalid data after declaration when I try to assign an id to canvas, but I don't see any other way of referencing the id's further below (for example e1). How do I reference e1 in my Python code?

<MyClockWidget>:
    face: face
    ticks: ticks
    el1: el1
    FloatLayout:
        id: face
        size_hint: None, None
        pos_hint: {"center_x":0.5, "center_y":0.5}
        size: 0.9*min(root.size), 0.9*min(root.size)
        canvas:
            id: cand
            Color:
                rgb: 0.5, 0.5, 0.5
            Ellipse:
                size: self.size     
                pos: self.pos
        canvas:
            Color:
                rgb: 0.1, 0.1, 0.1
            Ellipse:
                id: el1
                size: self.size     
                pos: self.pos
                angle_start: 0
                angle_end: 90
            Ellipse:
                id: el2
                size: self.size     
                pos: self.pos
                angle_start: 110
                angle_end: 130

推荐答案

我觉得用不到 instruction groups 有很好的文档记录，但这里有一个示例，说明如何使用它们以后访问 Canvas 元素.此示例还展示了如何使用属性来控制 Canvas 指令的各个方面:

I don't think the use of instruction groups in kv lang is well documented, but here is an example for how to use them to later access Canvas elements. This example also show how to use properties to control aspects of a Canvas instruction:

from kivy.app import App
from kivy.uix.slider import Slider
from kivy.lang import Builder
from kivy.graphics import Color

kv = """
#:kivy 1.9.1
BoxLayout:
    orientation: 'vertical'
    Widget:
        id: w_canvas
        my_color: (0, 1, 1)
        canvas:
            Color:
                rgb: self.my_color
            Rectangle:
                pos: self.pos
                size: (self.width/2, self.height/2)
            Color:
                group: 'b'
                rgb: (0, .8, 0)
            Ellipse:
                group: 'a'
                pos: (self.pos[0], self.pos[1] + self.height/2)
                size: (self.width/4, self.height/4)
            Ellipse:
                group: 'b'
                pos: (self.pos[0]+ self.width/2, self.pos[1] + self.height/2)
                size: (self.width/4, self.height/4)
    Button:
        text: 'Click me'
        on_release: app.handle_button()
"""
class Test(App):
    def build(self):
        return Builder.load_string(kv)
    def handle_button(self):
        # binding Canvas instruction property to Widget property
        self.root.ids.w_canvas.my_color = (.5, .2, 0)
        # Access single item of canvas instruction group
        an_ellipse = self.root.ids.w_canvas.canvas.get_group('a')[0]
        an_ellipse.pos = (an_ellipse.pos[0] + 10, an_ellipse.pos[1])
        # loop through all elements of canvas instruction group
        for gitem in self.root.ids.w_canvas.canvas.get_group('b'):
            if isinstance(gitem, Color):
                gitem.rgb = (0, .5, 1)
            try:
                gitem.size = (gitem.size[0] / 2.0, gitem.size[1])
            except:
                pass

Test().run()

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