問題描述

當(dāng)我嘗試將 id 分配給畫布時(shí)，我收到錯(cuò)誤 Invalid data after declaration，但我看不到任何其他引用該 id 的方式(例如 e1).如何在我的 Python 代碼中引用 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

推薦答案

我覺得用不到 instruction groups 有很好的文檔記錄，但這里有一個(gè)示例，說明如何使用它們以后訪問 Canvas 元素.此示例還展示了如何使用屬性來控制 Canvas 指令的各個(gè)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()

這篇關(guān)于如何在 Kivy 的畫布中引用孩子的 id?的文章就介紹到這了，希望我們推薦的答案對(duì)大家有所幫助，也希望大家多多支持html5模板網(wǎng)！