Kivy 不使用操作栏上的按钮更改屏幕

Question

The code I referred to is from ikolim's answer here: Why is my Kivy Actionbar gone?

This is my python code:

from kivy.app import App
from kivy.uix.screenmanager import ScreenManager,Screen
from kivy.properties import ObjectProperty
from kivy.uix.boxlayout import BoxLayout
from kivy.lang import Builder
from kivy.core.window import Window

Window.clearcolor = (1,1,1,1)

Builder.load_file("designdawkalamomarunong.kv")


class Menu(BoxLayout):
    manager = ObjectProperty(None)

class Add(Screen):
    pass

class Help(Screen):
    pass

class Credits(Screen):
    pass

class Manager(ScreenManager):
    addScreen = ObjectProperty(None)
    helpScreen = ObjectProperty(None)
    creditsScreen = ObjectProperty(None)

class AntsApp(App):

    def build(self):
        return Menu()


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

And this is the kivy code:

<Menu>:
    manager: screen_manager
    orientation: "vertical"
    ActionBar:
        size_hint_y: 0.1
        ActionView:
            ActionPrevious:
            ActionButton:
                text: "Add"
                on_release: app.root.current = "add"
            ActionButton:
                text:"Help"
                on_release: app.root.current = "help"
            ActionButton:
                text: "Credits"
                on_release: app.root.current = "credits"
    Manager:
        id: screen_manager

<Add>:
    text: "hello boi"

<Help>:
    text: "hello world"

<Credits>:
    text: "goodbye world lol"

<Manager>:
    id: screen_manager
    addScreen: addScreen
    helpScreen: helpScreen
     creditsScreen: creditsScreen

    Add:
        id: addScreen
        name: 'add'
        manager: screen_manager

    Help:
        id: helpScreen
        name: 'help'
        manager: screen_manager

    Credits:
        id: creditsScreen
        name: 'credits'
        manager: screen_manager

When I run it, this is the output:

When I click the buttons on the actionbar, it does not return anything. Should I add anything else? Thank you in advance :)

Edit: Tried doing this:

<Add>:
    Button:
        text: "hello boi"

and it worked but when i tried this:

<Add>:
    Label:
        text: "hello boi"

it did not work. What am I missing here?

Answer 1

Problems

kv file

1. Replace all occurrence of app.root.current with root.manager.current because root is a BoxLayout widget and not a ScreenManager widget.
2. Each screen is missing a Label widget before the text .
3. When you instantiate Button widget as children in each class rule for the Screen, the text is visible. But when you replace the Button widget with Label, the text is not visible. The reason is because the default color text for Label is white ( rgba=1, 1, 1, 1 ) and the color of the BoxLayout is also white. Therefore, you are not able to see the text. If using Label widget, add color: (0, 0, 0, 1) # black color text .

Example

kv file

#:kivy 1.11.0

<Menu>:
    manager: screen_manager
    orientation: "vertical"
    ActionBar:
        size_hint_y: 0.1
        ActionView:
            ActionPrevious:
            ActionButton:
                text: "Add"
                on_release: root.manager.current = "add"
            ActionButton:
                text:"Help"
                on_release: root.manager.current = "help"
            ActionButton:
                text: "Credits"
                on_release: root.manager.current = "credits"
    Manager:
        id: screen_manager

<Add>:
    Label:
        text: "hello boi"
        color: 0, 0, 0, 1   # black color text

<Help>:
    Label:
        text: "hello world"
        color: 0, 0, 0, 1   # black color text

<Credits>:
    Label:
        text: "goodbye world lol"
        color: 0, 0, 0, 1   # black color text

<Manager>:
    addScreen: addScreen
    helpScreen: helpScreen
    creditsScreen: creditsScreen

    Add:
        id: addScreen
        name: 'add'

    Help:
        id: helpScreen
        name: 'help'

    Credits:
        id: creditsScreen
        name: 'credits'

Output