Kivy ScreenManager 在条件下切换“开始”屏幕

Question

我是 kivy 的新手，想开始一个小应用项目。我想要达到的目标：

• 当您第一次启动应用程序时 -> 显示带有某种用户数据表单的屏幕
• 将数据存储在 JsonStore -> 转到主屏幕
• 下次运行应用程序->检查userdata是否在JsonStore中并直接进入主屏幕

到目前为止，我已经找到了一个可行的解决方案，但它的工作方式让我并不满意。我想要的是在 .kv 文件中创建 ScreenManager 和 Screens 并让 .py 文件执行逻辑（通过检查存储中是否存在用户数据来加载哪个屏幕）。

我试过了：

• 使用 ScreenManager 类 (def __init__) - 无效
• 从 .kv 文件中调用方法，如下所示（也不起作用）：

<WindowManager>:
    root.check_for_user()
    MainWindow:
    UserDataWindow:
<MainWindow>:
...

到目前为止，这是我的工作代码：

main.py:

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.properties import ObjectProperty
from kivy.storage.jsonstore import JsonStore

class LoginWindow(Screen):
    nick = ObjectProperty(None)
    isle = ObjectProperty(None)
    hemisphere_n = ObjectProperty(None)
    hemisphere_s = ObjectProperty(None)

    def submit(self):
        store = JsonStore('store.json')
        if self.hemisphere_n.state == 'down' and self.hemisphere_s.state == 'normal':
            store.put('user', nickname=self.nick.text, island=self.isle.text, hemisphere="north")
        elif self.hemisphere_n.state == "normal" and self.hemisphere_s.state == "down":
            store.put('user', nickname=self.nick.text, island=self.isle.text, hemisphere="south")

class MainWindow(Screen):
    pass        

class WindowManager(ScreenManager):
    pass

kv = Builder.load_file("my.kv")
sm = WindowManager()
store = JsonStore('store.json')
screens = [MainWindow(name="main"), LoginWindow(name="login")]

for screen in screens:
    sm.add_widget(screen)

if store.exists('user'):
    print("exists")
    sm.current = "main"
else:
    print("not found")
    sm.current = "login"

class MainApp(App):
    def build(self):
        return sm

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

我的.kv：

#:kivy 1.11.1

<MainWindow>:
    FloatLayout:
        Label:
            text:
        Button:
            text: "Go Back"
            pos_hint: {"x": 0.45, "top": 0.5}
            size_hint: (0.1, 0.05)
            on_release:
                app.root.current = "login"

<LoginWindow>:
    nick: nickname
    isle: island
    hemisphere_n: hemisphere_n
    hemisphere_s: hemisphere_s
    FloatLayout:
        Label:
            text: "Nickname:"
            pos_hint: {"x": 0.45, "top": 0.7}
            size_hint: (0.1, 0.05)
        TextInput:
            id: nickname
            multiline: False
            pos_hint: {"x": 0.4, "top": 0.65}
            size_hint: (0.2, 0.05)

        Label:
            text: "Island Name:"
            pos_hint: {"x": 0.45, "top": 0.6}
            size_hint: (0.1, 0.05)
        TextInput:
            id: island
            multiline: False
            pos_hint: {"x": 0.4, "top": 0.55}
            size_hint: (0.2, 0.05)
        Label:
            text: "Hemisphere:"
            pos_hint: {"x": 0.45, "top": 0.5}
            size_hint: (0.1, 0.05)
        ToggleButton:
            id: hemisphere_n
            text: "North"
            group: "hemisphere"
            state: "down"
            pos_hint: {"x": 0.41, "top": 0.45}
            size_hint: (0.08, 0.05)
        ToggleButton:
            id: hemisphere_s
            text: "South"
            group: "hemisphere"
            pos_hint: {"x": 0.51, "top": 0.45}
            size_hint: (0.08, 0.05)
        Button:
            text: "Submit"
            pos_hint: {"x": 0.45, "top": 0.38}
            size_hint: (0.1, 0.05)
            on_press:
                root.submit()
            on_release:
                app.root.current = "main"

请忽略某些地方的松散端。在继续之前，我想先完成这项工作。 它现在进入主屏幕（当我将屏幕添加到屏幕管理器时），然后检查用户数据并最终切换到登录。你有什么建议吗？ 提前致谢。

Answer 1

您几乎可以将Screen 选择逻辑放在您想要的任何位置。这是将其放入 WindowManager 类的示例：

class WindowManager(ScreenManager):
    def select_start_screen(self):
        store = JsonStore('store.json')

        self.transition = NoTransition()
        if store.exists('user'):
            print("exists")
            self.current = "main"
        else:
            print("not found")
            self.current = "login"
        self.transition = SlideTransition()

然后你可以在你的build()方法中调用select_start_screen()：

class MainApp(App):
    def build(self):
        sm.select_start_screen()
        return sm

Answer 2

您看到的是transition 动画。您可以像这样使用NoTransition() 来消除这种情况：

sm.transition = NoTransition()
if store.exists('user'):
    print("exists")
    sm.current = "main"
else:
    print("not found")
    sm.current = "login"
sm.transition = SlideTransition()

Answer 3

在@John 的回答中先添加一个空白屏幕怎么样。

sm.add_widget(Screen(name='blank'))
for screen in screens:
    sm.add_widget(screen)