MDButton animation incomplete when changing screens.

[RobertFlatt]

Description of the Bug

When a button is used to switch screens, on returning to the first screen the button is seen as still elevated.

Seems to me like this is the expected behavior of Kivy (because the button is no longer visible it does not see the change in elevation event) but not of KivyMD.

It is possible this is an enhancement request. Since only the programmer knows the use of a button, the resolution may be to provide an api to allow the programmer to immediately reset the button elevation. A programmer might for example call this api on_release. Simply setting button.elevation = 0 from on_release does not have any effect.

In the example below, moving the cursor resets the elevation (presumably related to hover). This is not always the case, for example in tabs content, however this stickiness may be related to #1663 .

Code and Logs

from kivymd.app import MDApp
from kivy.lang import Builder

from kivymd.uix.screen import MDScreen
from kivymd.uix.screenmanager import MDScreenManager

Builder.load_string("""
<Screen1>:
    md_bg_color: self.theme_cls.backgroundColor
    MDBoxLayout:
        orientation:'vertical'
        MDLabel:
            text: 'Press "Go to Screen 2" Button'
            halign: "center"
        MDButton:
            on_release: root.manager.current = 'Two'
            pos_hint: {"center_x": .5, "center_y": .5}
            size_hint_y:0.5
            MDButtonText
                text: 'Go to Screen 2'
        MDLabel:

<Screen2>:
    md_bg_color: self.theme_cls.backgroundColor
    MDBoxLayout:
        orientation:'vertical'
        MDLabel:
            text: 'Press "Go to Screen 1" Button\\nThen look at the elevation of the Button in Screen 1\\nBEFORE moving the cursor,\\nTHEN move the cursor.'
            halign: "center"
        MDButton:
            style: "elevated"
            pos_hint: {"center_x": .5, "center_y": .5}
            on_release: root.manager.current = 'One'
            MDButtonText
                text: 'Go to Screen 1'
        MDLabel:
            size_hint_y:0.2
""")

class Screen1(MDScreen):
    pass

class Screen2(MDScreen):
    pass

class TestApp(MDApp):

    def build(self):
        sm = MDScreenManager()
        sm.add_widget(Screen1(name='One'))
        sm.add_widget(Screen2(name='Two'))
        return sm

TestApp().run()

Screenshots

Versions

• OS: Windows 11
• Python: 3.11.1
• Kivy: 2.3.0
• KivyMD: 2.0.1.dev0

[HeaTTheatR]

I have not found any bugs in this code yet. Maybe you have screenshots that show the bug?

[RobertFlatt]

Perhaps I don't understand the expected behavior. To try to be clearer I added a "For comparison" button to the first screen (code below) as a reference. The screen shot is the first screen on return from the second screen, and without moving the cursor. The Comparison button is a different elevation to the "Go to screen 2" button.

from kivymd.app import MDApp
from kivy.lang import Builder

from kivymd.uix.screen import MDScreen
from kivymd.uix.screenmanager import MDScreenManager

Builder.load_string("""
<Screen1>:
    md_bg_color: self.theme_cls.backgroundColor
    MDBoxLayout:
        orientation:'vertical'
        MDLabel:
            text: 'Press "Go to Screen 2" Button'
            halign: "center"
        MDButton:
            on_release: root.manager.current = 'Two'
            pos_hint: {"center_x": .5, "center_y": .5}
            size_hint_y:0.5
            MDButtonText
                text: 'Go to Screen 2'
        MDButton:
            pos_hint: {"center_x": .5, "center_y": .5}
            size_hint_y:0.5
            MDButtonText
                text: 'For comparison, no action'
        MDLabel:

<Screen2>:
    md_bg_color: self.theme_cls.backgroundColor
    MDBoxLayout:
        orientation:'vertical'
        MDLabel:
            text: 'Press "Go to Screen 1" Button\\nThen look at the elevation of the Button in Screen 1\\nBEFORE moving the cursor,\\nTHEN move the cursor.'
            halign: "center"
        MDButton:
            style: "elevated"
            pos_hint: {"center_x": .5, "center_y": .5}
            on_release: root.manager.current = 'One'
            MDButtonText
                text: 'Go to Screen 1'
        MDLabel:
            size_hint_y:0.2
""")

class Screen1(MDScreen):
    pass

class Screen2(MDScreen):
    pass

class TestApp(MDApp):

    def build(self):
        sm = MDScreenManager()
        sm.add_widget(Screen1(name='One'))
        sm.add_widget(Screen2(name='Two'))
        return sm

TestApp().run()

[HeaTTheatR]

Now I understand what the problem is, thanks