Myujth

Well, I'm creating a Kivy app in which you can select only one of many statuses. Every status has his own Button and the selected status has a different background_color from the others.

The problem is that sometimes (apparently random) after clicking a button, two of them stays with his background changed at the same time. The strange thing is that I'm checking the background_color of those elements and it doesn't match with the result that I'm seeing on the screen.

So, the background_color property has one color but another one is being rendered on the screen.

Relevant kv file section:

<StatusButtonsContainer>:
 cols: 2
 spacing: 8
 padding: 0,16,0,0

<StatusButton>:
 selected: False
 text: self.status_name
 on_release: app.on_change_status_click(self.status_name)
 font_size: '16'
 background_color: self.back_color if self.selected else (0.259, 0.259, 0.259,1)
 background_normal: ''
 background_down: ''
 background_disabled_normal: ''

This is how I'm creating the Button widgets dinamically:

class StatusButtonsContainer(GridLayout):

 def __init__(self, **kwargs):
 super(StatusButtonsContainer, self).__init__(**kwargs)
 for name, color in config.statuses.items():
 button = StatusButton(status_name=name, back_color=color)
 self.add_widget(button)


class StatusButton(Button):
 status_name = StringProperty()
 back_color = ListProperty()

And this the function that is executed when the button is pressed:

class ControlsScreen(Screen):

 def change_selected_status(self, status):
 for button in self.ids.buttons_container.children:
 if button.status_name == status:
 button.selected = True
 button.disabled = True
 print('Status ' + button.status_name + ' was selected.')
 print('background_color:' + str(button.background_color))
 else:
 button.selected = False
 button.disabled = status in ['printing', 'preparing', 'paused']
 print('Status ' + button.status_name + ' was NOT selected.')
 print('background_color:' + str(button.background_color))

It's even more weird that this is happening on a Raspberry Pi 3 with Raspbian, but I'm not able to reproduce it on a Windows machine... I double checked that the [input] section in the config is correct and the buttons are being pressed only once.

Versions

• Python: 3.6.0


• OS: Raspbian GNU/Linux 9 (stretch)


• Kivy: 1.10.1

Finally, the problem was that I was updating the UI in a thread different from the main thread.

In my application, the button status can be changed either from the UI directly or from a web socket message. So, when the button's background_color was changed through web socket, the UI update was called by another thread and, for some reason, that was causing the issue.

I've solved it with the @mainthread decorator:

@mainthread
def change_status_ui(self, status):
 self.get_screen('Controls').change_selected_status(status)
 self.get_screen('Status').change_status(status)

Now, it doesn't matter which thread call this method, it will be executed on the main thread.