滚动视图中的 Kivy 背景

Question

测试应用程序摘要： 我正在编写一个带有可滚动视图（名为 Scroller）的 Kivy 应用程序，其中包含许多要查看的字段（名为 Field）。这些单独的字段有时真的很难区分，所以我决定为每个字段使用交替的背景颜色来帮助区分彼此。我的测试应用程序使用 20 个单独的字段，每个字段在深灰色和深灰色之间交替。

测试试验： 启动应用程序，程序看起来很棒。交替的背景看起来很好。即使我向下滚动应用程序看起来也很好。但是，当我向上滚动应用程序时，应用程序似乎变得很奇怪。文本随应用程序滚动，但背景不滚动。更好的是（讽刺地），文本开始消失在他们的邻居背景中。当我再次向下滚动（通过最远向上滚动点的点）时，问题似乎消失了。

简单的问题描述：Field 的“背景颜色”在向上滚动事件期间弄乱了应用程序。

旁注：我还注意到应用程序在滚动过多后变得有点迟钝。我对 Kivy 的绘制周期不是很熟悉，但是 blitting 背景不应导致过度减速。

测试应用：

import kivy
kivy.require('1.0.7')

from kivy.app import App
from kivy.uix.gridlayout import GridLayout
from kivy.uix.scrollview import ScrollView
from kivy.uix.label import Label
from kivy.uix.button import Button
from kivy.graphics import Color, Rectangle

class Main(App):
    def build(self):
        self.root = GridLayout(rows = 1)
        self.root.add_widget(Scroller())
        return self.root

class Scroller(ScrollView):
    def __init__(self):
        ScrollView.__init__(self)
        self.view = GridLayout(cols = 1, size_hint = (1, None))
        self.add_widget(self.view)
        self.view.bind(minimum_height = self.view.setter('height'))

        for i in range(20):
            self.view.add_widget(Field('Test field {}'.format(i),i%2 is 0))

class Field(GridLayout):
    def __init__(self, name, bg):
        assert isinstance(name, str)
        assert isinstance(bg, bool)
        self.bg = bg
        GridLayout.__init__(self,
                            rows = 1,
                            padding = 10,
                            size = (0, 60),
                            size_hint = (1, None))
        self.add_widget(Label(text = name))
        self.add_widget(Button(text = 'Test button',
                               size = (200, 0),
                               size_hint = (None, 1)))
        self.bind(pos = self.change_background)
        self.bind(size = self.change_background)

    def change_background(self, *args):
        with self.canvas.before:
            if self.bg:
                Color(0.2, 0.2, 0.2, mode = 'rgb')
            else:
                Color(0.1, 0.1, 0.1, mode = 'rgb')
            Rectangle(pos = self.pos, size = self.size)

if __name__ in ('__main__', '__android__'):
    app = Main()
    app.run()

Answer 1

def change_background(self, *args):
        self.canvas.before.clear()#<- clear previous instructions
        with self.canvas.before:
            if self.bg:
                Color(0.2, 0.2, 0.2, mode = 'rgb')
            else:
                Color(0.1, 0.1, 0.1, mode = 'rgb')
            Rectangle(pos = self.pos, size = self.size)

每次字段的位置/大小发生变化时，您都在向画布添加/堆积指令，而无需清除先前的指令。

您还应该考虑将 kv 用于除小型 sn-p 之外的任何东西，它最终会为您节省大量时间。您可以像这样使用 kv 转换代码 ::

import kivy
kivy.require('1.0.7')

from kivy.app import App
from kivy.uix.gridlayout import GridLayout
from kivy.uix.scrollview import ScrollView
from kivy.properties import ObjectProperty, BooleanProperty
from kivy.lang import Builder

Builder.load_string('''
<Scroller>
    # root is Scroller here
    # create a new ObjectProperty in kv that holds the ref to Gridlayout
    # so you can access the instance in python code
    view: glayout
    GridLayout:
        id: glayout
        cols: 1
        size_hint: (1, None)
        height: self.minimum_height

<Field>
    canvas.before:
        Color:
            rgba: (0.2, 0.2, 0.2, 1) if self.bg else (0.1, 0.1, 0.1, 1)
        Rectangle:
            # binding properties is done implicitly and instructions aren't
            # piled up while doing that.
            pos: self.pos
            # self here refers to Field as `self` is supposed to refer to the
            # Widget not the drawing instruction
            size: self.size
    rows: 1
    padding: 10
    size: (0, 60)
    size_hint: (1, None)
    Label:
        text: root.name
    Button:
        text: 'test button'
        size: (200, 0)
        size_hint: (None, 1)
''')


class Main(App):

    def build(self):
        self.root = GridLayout(rows = 1)
        self.root.add_widget(Scroller())
        return self.root


class Scroller(ScrollView):
    def __init__(self, **kwargs):
        super(Scroller, self).__init__(**kwargs)
        for i in range(20):
            # access self.view that was set in kv
            self.view.add_widget(
                                Field(
                                    name = 'Test field {}'.format(i),
                                    bg = i%2 is 0))

class Field(GridLayout):

    # use  kivy's Properties so it becomes easier to observe and apply changes
    # as a plus these can also be directly used in kv. As a advantage of using this now
    # you can change name and bg dynamically and the changes should be reflected on
    # screen
    name = ObjectProperty('Test field uninitialized')

    bg = BooleanProperty(False)


if __name__ in ('__main__', '__android__'):
    app = Main()
    app.run()