A delayed resize layout in Kivy

Sat 13 July 2019

A user on the Kivy Discord just raised the question of how to delay widget updates during resize events. The problem was that the widgets did some heavy processing (generating matplotlib graphs) that would be very slow if called for every tiny update during a larger resize event.

This is a good opportunity to return to the flexibility of Kivy layouts. It’s very easy to add some simple behaviour that delays updates until a short period has passed without the size changing. Here’s a quick implementation I threw together:

from kivy.uix.anchorlayout import AnchorLayout
from kivy.clock import Clock
from kivy.properties import ObjectProperty, NumericProperty

from functools import partial

class DelayedResizeLayout(AnchorLayout):

    do_layout_event = ObjectProperty(None, allownone=True)

    layout_delay_s = NumericProperty(0.2)

    def do_layout(self, *args, **kwargs):
        if self.do_layout_event is not None:
            self.do_layout_event.cancel()
        real_do_layout = super().do_layout
        self.do_layout_event = Clock.schedule_once(
            lambda dt: real_do_layout(*args, **kwargs),
            self.layout_delay_s)

This layout could be used as the root widget of a whole application, to delay the resizing of all the content, or somewhere within the app to delay only a small part of it.

And a simple example:

from kivy.uix.button import Button
from kivy.base import runTouchApp

button = Button(text='example button')
layout = DelayedResizeLayout()
layout.add_widget(button)
runTouchApp(layout)

Category: kivy Tagged: python kivy