Python – Kivy – Hiding a widget as soon as screen shows up

June 2, 2022

I want to hide the progress bar at below code as soon as screen appears. In order to do that I defined a hide_widget function and added the code to "on_pre_enter" section. However it doesn’t work. What am I missing here ?

By the way if you can introduce a shorter way to hide a widget in kivy, it is also very welcome.

from kivy.app import App
from kivy.uix.widget import Widget
from kivy.lang import Builder

Builder.load_string("""

<MyLayout>

    BoxLayout:
        orientation: "vertical"
        size: root.width, root.height
        spacing: 20
        padding: 50

        Button:
            text: "Test"

        ProgressBar:
            id:         pgb_excel_read
            min:        0
            max:        100
            value:      0
            size_hint:  ( 1, 0.1)

""")

def hide_widget(wid, dohide=True):

    if hasattr(wid, 'saved_attrs'):
        if not dohide:
            wid.height, wid.size_hint_y, wid.opacity, wid.disabled = wid.saved_attrs
            del wid.saved_attrs
    elif dohide:
        wid.saved_attrs = wid.height, wid.size_hint_y, wid.opacity, wid.disabled
        wid.height, wid.size_hint_y, wid.opacity, wid.disabled = 0, None, 0, True


class MyLayout(Widget):

    def on_pre_enter(self, *args):
        hide_widget(self.ids.pgb_excel_read, True)

class MyApp(App):
    def build(self):
        return MyLayout()

if __name__ == '__main__':
    MyApp().run()

>Solution :

on_pre_enter function is only avaliable for Screen classes. But you try to use it in your custom Widget. So there is a nothing to trigger this function. We can trigger it by __init__:

class MyLayout(Widget):
    def __init__(self):
        super(MyLayout, self).__init__()
        hide_widget(self.ids.pgb_excel_read, True)

For hide any widget we just need to change 2 things:

Disabled : True
Opacity : 0

Short way to do that, lets stop triggering any function and just change variables: (Also Remove hide_widget function)

class MyLayout(Widget):
    def __init__(self):
        super(MyLayout, self).__init__()
        # hide_widget(self.ids.pgb_excel_read, True)
        self.ids.pgb_excel_read.opacity = 0
        self.ids.pgb_excel_read.disabled = True