在 MDTab 中显示来自 API 请求的数据

Question

我正在尝试学习使用 Python 进行编码，并正在制作一个应用程序来跟踪使用 KivyMD 的用户的会话时间。目前，我试图通过从我的数据库中的 api 调用获取 json 数据来显示总时间。我编写了一个函数来获取和处理 json 数据以计算总时间。当 Mijn sessie 选项卡加载时，该函数必须自动触发以在 MDLabel time_label 中显示数据（变量：total_minutes）。这就是我非常困惑的地方。

我在 Kivy 中找到了 on_pre_enter 函数，它在屏幕加载时触发该函数，但它仅在 Screen 类中有效，在 Tabs 类中无效。如果我在Screen 类中执行python 逻辑，我不知道如何在Tabs 类中使用python 变量。我用 Objectproperty 和 Stringproperty 尝试了很多东西，但都没有成功。我认为我在这里遗漏了一些更大的东西。

当您自己看到应用程序时，我将发布代码以使事情更清楚。出于安全原因，我用一个产生相同结果（浮点数）的小函数替换了 api 请求函数。

非常感谢！

main.py 文件

from kivymd.app import MDApp
from kivy.lang import Builder
from kivy.core.window import Window
from kivy.uix.screenmanager import ScreenManager, Screen
from kivymd.uix.tab import MDTabsBase
from kivymd.font_definitions import fonts
from kivymd.icon_definitions import md_icons
from kivy.uix.floatlayout import FloatLayout
from kivy.properties import ObjectProperty, StringProperty
from kivy.uix.widget import Widget
from kivymd.uix.label import MDLabel
import requests
import json
from datetime import datetime

Window.size = (300, 500) # voor develop doeleinden mobielscherm

class Screen1(Screen):
    pass

    def on_pre_enter(self, *args):

        def func(a, b):
            total_minutes = a - b
            return total_minutes

        print(func(3000,1500))

class Screen2(Screen):
    pass


class Screen3(Screen):
    pass


class Screen4(Screen):
    pass


class Tab_mijn_sessie(FloatLayout, MDTabsBase):
    pass


class Tab_alarm(FloatLayout, MDTabsBase):
    pass


class Tab_actieve_drinkers(FloatLayout, MDTabsBase):
    pass


class Tab_score(FloatLayout, MDTabsBase):
    pass


class Tab_achievments(FloatLayout, MDTabsBase):
    pass


class Tab_historie(FloatLayout, MDTabsBase):
    pass


class DemoApp(MDApp):

    def build(self):

        self.theme_cls.primary_palette = 'Red'
        self.theme_cls.theme_style = 'Dark'
        screen = Builder.load_file('demo_file.kv')

        return screen


DemoApp().run()

demo_file.kv 文件

Screen:

    NavigationLayout:

        ScreenManager:
            id:screen_manager

            Screen1:
                name: 'home_screen'

                BoxLayout:
                    name: 'home_layout'
                    orientation: 'vertical'

                    MDToolbar:
                        title: 'Huidige sessie'
                        left_action_items: [['menu', lambda x: nav_drawer.set_state("open")]]
                        specific_text_color: 1,1,1,1

                    MDTabs:
                        id:home_tabs
                        tab_bar_height: '35dp'
                        text_color_active: 1,1,0,1
                        text_color_normal: 0,0,0,1
                        color_indicator: 0.95, 0.95, 0.1, 1
                        tab_indicator_anim: True
                        anim_duration: 0.2
                        tab_indicator_height: '3dp'

                        Tab_mijn_sessie:
                            text: 'Mijn sessie'

                        Tab_alarm:
                            text: 'Alarm'

                        Tab_actieve_drinkers:
                            text: 'Actieve drinkers'

                    MDToolbar:
                        id: bottom_toolbar_scr1
                        name: 'bottom_toolbar'
                        specific_text_color: 1,1,1,1
                        title: '          Sessie inactief..'

            Screen2:
                name: 'statistieken_screen'

                BoxLayout:
                    name: 'statistieken_layout'
                    orientation: 'vertical'

                    MDToolbar:
                        title: 'Statistieken'
                        left_action_items: [['menu', lambda x: nav_drawer.set_state("open")]]
                        specific_text_color: 1,1,1,1

                    MDTabs:
                        id:home_tabs
                        tab_bar_height: '35dp'
                        text_color_active: 1,1,0,1
                        text_color_normal: 0,0,0,1
                        color_indicator: 0.95, 0.95, 0.1, 1
                        tab_indicator_anim: True
                        anim_duration: 0.2
                        tab_indicator_height: '3dp'

                        Tab_score:
                            text: 'Scorebord'

                        Tab_achievments:
                            text: 'Achievements'

                        Tab_historie:
                            text: 'Historie'

                    MDToolbar:
                        id: bottom_toolbar_scr2
                        name: 'bottom_toolbar'
                        specific_text_color: 1,1,1,1
                        title: '          Sessie inactief..'


            Screen3:
                name: 'logout_screen'

                BoxLayout:
                    name: 'logout_layout'
                    orientation: 'vertical'

                    MDToolbar:
                        title: 'Uitloggen'
                        left_action_items: [['menu', lambda x: nav_drawer.set_state("open")]]
                        specific_text_color: 1,1,1,1

                    Widget:


            Screen4:
                name: 'profile_screen'

                BoxLayout:
                    name: 'profile_layout'
                    orientation: 'vertical'

                    MDToolbar:
                        title: 'Profiel'
                        left_action_items: [['menu', lambda x: nav_drawer.set_state("open")]]
                        specific_text_color: 1,1,1,1

                    Widget:

                    MDToolbar:
                        id: bottom_toolbar_scr4
                        name: 'bottom_toolbar'
                        specific_text_color: 1,1,1,1
                        title: '          Sessie inactief..'

        MDNavigationDrawer:
            id:nav_drawer

            BoxLayout:
                orientation: 'vertical'
                spacing: '8dp'
                padding: '8dp'

                Image:
                    source: 'avatar.jpg'


                MDLabel:
                    text: '     Name'
                    front_style: 'Subtitle1'
                    size_hint_y: None
                    height: self.texture_size[1]

                MDLabel:

                    text: '     email@hotmail.com'
                    front_style: 'Caption'
                    size_hint_y: None
                    height: self.texture_size[1]

                ScrollView:
                    MDList:

                        OneLineIconListItem:
                            theme_text_color: 'Custom'
                            text_color: 244/255, 67/255, 54/255, 1
                            text: 'Huidige sessie'


                            on_press:
                                screen_manager.current = 'home_screen'
                                nav_drawer.set_state("close")

                            IconLeftWidget:
                                theme_text_color: 'Custom'
                                text_color: 0.95, 0.95, 0.1, 1
                                icon: 'beer'
                                on_press:
                                    screen_manager.current = 'home_screen'
                                    nav_drawer.set_state("close")

                        OneLineIconListItem:
                            theme_text_color: 'Custom'
                            text_color: 244/255, 67/255, 54/255, 1
                            text: 'Statistieken'

                            on_press:
                                screen_manager.current = 'statistieken_screen'
                                nav_drawer.set_state("close")

                            IconLeftWidget:
                                icon: 'history'
                                theme_text_color: 'Custom'
                                text_color: 0.95, 0.95, 0.1, 1
                                on_press:
                                    screen_manager.current = 'historie_screen'
                                    nav_drawer.set_state("close")

                        OneLineIconListItem:
                            theme_text_color: 'Custom'
                            text_color: 244/255, 67/255, 54/255, 1
                            text: 'Profiel'

                            on_press:
                                screen_manager.current = 'profile_screen'
                                nav_drawer.set_state("close")

                            IconLeftWidget:
                                icon: 'face-profile'
                                theme_text_color: 'Custom'
                                text_color: 0.95, 0.95, 0.1, 1
                                on_press:
                                    screen_manager.current = 'profile_screen'
                                    nav_drawer.set_state("close")

                        OneLineIconListItem:
                            theme_text_color: 'Custom'
                            text_color: 244/255, 67/255, 54/255, 1
                            text: 'Uitloggen'
                            on_press:
                                screen_manager.current = 'logout_screen'
                                nav_drawer.set_state("close")

                            IconLeftWidget:

                                icon: 'logout'
                                theme_text_color: 'Custom'
                                text_color: 0.95, 0.95, 0.1, 1
                                on_press:
                                    screen_manager.current = 'logout_screen'
                                    nav_drawer.set_state("close")

<Tab_mijn_sessie>:

    MDLabel:
        text: 'Total time'
        font_style: 'H6'
        halign: 'center'
        pos_hint: {"center_x": .5, "center_y": .4}
    MDLabel:
        id : time_label
        text: '(this has to display the total amount of time)'
        font_style: 'Body2'
        halign: 'center'
        pos_hint: {"center_x": .5, "center_y": .3}

    MDFlatButton:
        theme_text_color: 'Custom'
        text_color: 1,1,1,1
        halign: 'center'
        text:'Activate session'
        user_font_size: "48sp"
        pos_hint: {"center_x": .5, "center_y": .7}
        on_press:
            app.root.ids.bottom_toolbar_scr1.title = '          Sessie actief!'
            app.root.ids.bottom_toolbar_scr1.specific_text_color = 0,1,0,1
            app.root.ids.bottom_toolbar_scr2.title = '          Sessie actief!'
            app.root.ids.bottom_toolbar_scr2.specific_text_color = 0,1,0,1
            app.root.ids.bottom_toolbar_scr4.title = '          Sessie actief!'
            app.root.ids.bottom_toolbar_scr4.specific_text_color = 0,1,0,1


<Tab_alarm>:
    MDLabel:
        halign: 'center'
        text:'Alarm'
        user_font_size: "48sp"
        pos_hint: {"center_x": .5, "center_y": .5}


<Tab_actieve_drinkers>:
    MDLabel:
        halign: 'center'
        text:'Actieve drinkers'
        user_font_size: "48sp"
        pos_hint: {"center_x": .5, "center_y": .5}

<Tab_score>:
    MDLabel:
        halign: 'center'
        text:'Scorebord'
        user_font_size: "48sp"
        pos_hint: {"center_x": .5, "center_y": .5}

<Tab_achievments>:
    MDLabel:
        halign: 'center'
        text:'Achievments'
        user_font_size: "48sp"
        pos_hint: {"center_x": .5, "center_y": .5}

<Tab_historie>:
    FloatLayout:
        MDLabel:
            halign: 'center'
            text:'Historie'
            user_font_size: "48sp"
            pos_hint: {"center_x": .5, "center_y": .5}

        MDFlatButton:
            id: flat
            text: 'druk hier'
            pos_hint: {"center_x": .5, "center_y": 0.4}

Answer 1

from kivy.lang import Builder
from kivy.uix.floatlayout import FloatLayout

from kivymd.app import MDApp
from kivymd.uix.tab import MDTabsBase
from kivymd.icon_definitions import md_icons

KV = '''
BoxLayout:
    orientation: "vertical"

    MDToolbar:
        title: "Example Tabs"

    MDTabs:
        id: tabs
        on_tab_switch: app.on_tab_switch(*args)


<Tab>:

    MDIconButton:
        id: icon
        icon: app.icons[0]
        user_font_size: "48sp"
        pos_hint: {"center_x": .5, "center_y": .5}
'''


class Tab(FloatLayout, MDTabsBase):
    '''Class implementing content for a tab.'''


class Example(MDApp):
    icons = list(md_icons.keys())[15:30]

    def build(self):
        return Builder.load_string(KV)

    def on_start(self):
        for name_tab in self.icons:
            self.root.ids.tabs.add_widget(Tab(text=name_tab))

    def on_tab_switch(
        self, instance_tabs, instance_tab, instance_tab_label, tab_text
    ):
        '''Called when switching tabs.

        :type instance_tabs: <kivymd.uix.tab.MDTabs object>;
        :param instance_tab: <__main__.Tab object>;
        :param instance_tab_label: <kivymd.uix.tab.MDTabsLabel object>;
        :param tab_text: text or name icon of tab;
        '''

        count_icon = [k for k, v in md_icons.items() if v == tab_text]
        instance_tab.ids.icon.icon = count_icon[0]


Example().run()

https://kivymd.readthedocs.io/en/latest/components/tabs/index.html#kivymd.uix.tab.MDTabs.on_tab_switch