Kivy widget's opacity doesn't update visually - python-3.x

Question

I want to hide one widget and show another on button's click. I do it by changing opacity form 1 to 0 and from 0 to 1. The firt widget becomes invisible, but the second is not showing.
This is my python file:
from kivy.app import App
from kivy.uix.widget import Widget
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.properties import NumericProperty
from kivy.config import Config
Config.set('graphics', 'width', '1920')
Config.set('graphics', 'height', '1080')
Config.set('graphics', 'fullscreen', 1)
class FirstScreen(Screen):
pass
class SecondScreen(Screen):
pass
class MyScreenManager(ScreenManager):
pass
class PasswordEntryWidget(BoxLayout):
def checkPswd(instance, pswd):
if (pswd == "123"):
instance.parent.opacity = 0
instance.parent.disabled = True
instance.parent.parent.ids.settingsWgt.opacity = 1.0
#print(instance.parent.parent.ids.settingsWgt.size_hint)
class SettingsEntryWidget(BoxLayout):
def checkPswd(instance, pswd):
if (pswd == "123"):
print ("It's OK!")
class MyApp(App):
def build(self):
return MyScreenManager()
if __name__ == '__main__':
MyApp().run()
This is my.kv:
#:kivy 1.11.1
#:include loginWidgets.kv
<MyScreenManager>:
FirstScreen:
SecondScreen:
<FirstScreen>:
name: "FirstScreen"
canvas.before:
Rectangle:
pos: self.pos
size: self.size
source: 'img/background.png'
FloatLayout:
size: root.size
PasswordEntryWidget:
id: passwordWgt
size_hint: 0.2, 0.1
pos_hint: {'top': 0.35, 'right': 0.7}
SettingsEntryWidget:
id: settingsWgt
opacity: 0
disabled: True
size_hint: 0.2, 0.32
pos_hint: {'top': 0.35, 'right': 0.95}
<SecondScreen>:
name: "SecondScreen"
Label:
color: 1,1,1,1
font_size: 10
center_x: root.width/4
top: root.top - 50
text: "Lalalala"
And this is loginWidgets.kv:
#:kivy 1.11.1
<PasswordEntryWidget>:
orientation: "vertical"
spacing: 20
#padding: 50
TextInput:
id: adminPswdLine
multiline: False
password: True
size_hint_y: None
height: 30
font_size: self.height - 10
Button:
id: "takeAdminPswd"
size_hint_x: 0.5
pos_hint: {'center_x': 0.5}
on_press: root.checkPswd(adminPswdLine.text)
<SettingsEntryWidget>:
orientation: "vertical"
spacing: 20
#padding: 50
TextInput:
id: host
padding: [5, 2, 0, 5]
text: ""
multiline: False
password: False
size_hint_y: None
height: 30
font_size: self.height - 10
Button:
id: "takeSettings"
size_hint_x: 0.5
pos_hint: {'center_x': 0.5}
on_press: root.checkPswd(adminPswdLine.text)
As I said, the first part works well. PasswordWgt hide perfectly, but SettingsWgt doesn't become visible. When I print it's opacity after - it gives 1, so widget must be visible, but it's not. I checked ids and what elements are there and needed widget is there with this id.
Is it a bug or I do something wrong?

Answer 1

The problem is that your are changing the opacity of the container (FloatLayout) instead of the PasswordEntryWidget. Just change:
class PasswordEntryWidget(BoxLayout):
def checkPswd(instance, pswd):
if (pswd == "123"):
instance.parent.opacity = 0
instance.parent.disabled = True
instance.parent.parent.ids.settingsWgt.opacity = 1.0
to:
class PasswordEntryWidget(BoxLayout):
def checkPswd(instance, pswd):
if (pswd == "123"):
instance.opacity = 0
instance.disabled = True
instance.parent.parent.ids.settingsWgt.opacity = 1.0
and I think it will work as you desire.