使用带有 Kivy 按钮布局的 ScreeManager 时的问题不再有效

Question

所以我在尝试使用屏幕管理器时遇到了问题。因为我必须创建我的屏幕类现在是 (Screen) 而不是 (GridLayout) 才能使用 screenmanager，例如，按钮/布局管理不能再在 python 中控制了吗？它曾经在屏幕上布置 5 列和 3 行，总共 15 个按钮。现在它只显示一个大的（屏幕）而不是网格布局。

class LandingScreen(Screen):
def build(self):
    return presentation
def __init__(self, **kwargs):
    super(LandingScreen, self).__init__(**kwargs)
    self.cols = 5
    self.buttons = []  # add references to all buttons here

    # Loop to make 20 different buttons on screen
    for x in range(15):
        self.buttons.append(Button(text='button ' + str(x)))  # make a reference to the button before adding it in
        self.add_widget(self.buttons[x])
        self.buttons[x].background_normal = 'YOUTUBE.png'

此处的按钮和列设置用于使用此循环创建 3 行，每行 5 个按钮，因为我将 (Screen) 添加到类而不是 (GridLayout)，所以它没有。我宁愿不在 .kv 文件中创建所有按钮，因为我认为在 .py 中更容易管理并且对我来说更有意义。

这是我的 .kv 文件：

<GridLayout>:
    cols: 5
    height: 480
    width: 800
    spacing: 25, 20
    padding: 25,25

<MyScreenManager>:
    LandingScreen:
    InputScreen:

<InputScreen>:
    AnchorLayout:

<LandingScreen>:
    GridLayout:
        cols: 5
        height: 480
        width: 800
        spacing: 25, 20
        padding: 25,25

这显然是多余的，因为我试图弄清楚如何让所有 15 个按钮再次显示，而不仅仅是一个。

谢谢！

Answer 1

您希望将按钮添加到 GridLayout 内的 Screen，而不是直接添加到 Screen。为此，请使用id 来引用GridLayout。

但是，您不能在__init__ 方法中使用id，因为在相应的小部件完全初始化之前不会应用kv 文件中定义的规则。 Ryan Pi 在这个问题中正确提供了解决方案：

Why can't I access the Screen.ids?

另一方面，稍后要更改屏幕，您必须在屏幕中定义 name 属性。

你的代码应该是：

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.button import Button
from kivy.clock import Clock


kv_text='''\

<MyScreenManager>:
    LandingScreen:
    InputScreen:

<InputScreen@Screen>:
    name: 'input_sc'
    AnchorLayout:
        id: anchor_1

<LandingScreen@Screen>:
    name: 'landing_sc'
    GridLayout:
        id: grid_1
        cols: 5
        height: 480
        width: 800
        spacing: 25, 20
        padding: 25,25
'''

class MyScreenManager(ScreenManager):
    pass


class LandingScreen(Screen):
    def __init__(self, **kwargs):
        super(LandingScreen, self).__init__(**kwargs)
        self.buttons = [] # add references to all buttons here
        Clock.schedule_once(self._finish_init)

    def _finish_init(self, dt):
        self.ids.grid_1.cols = 5

        # Loop to make 20 different buttons on screen
        for x in range(15):
            self.buttons.append(Button(text='button {}'.format(x)))
            self.ids.grid_1.add_widget(self.buttons[x])
            self.buttons[x].background_normal = 'YOUTUBE.png'

class MyKivyApp(App):
    def build(self):
        return MyScreenManager()

def main():
    Builder.load_string(kv_text)
    app = MyKivyApp()
    app.run()

if __name__ == '__main__':
    main()

如果您想使用Properties 而不是ids 方法（请参阅documentation），您应该执行以下操作：

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.button import Button
from kivy.clock import Clock
from kivy.properties import ObjectProperty


kv_text='''\

<MyScreenManager>:
    LandingScreen:
    InputScreen:

<InputScreen@Screen>:
    name: 'input_sc'
    AnchorLayout:
        id: anchor_1

<LandingScreen@Screen>:
    name: 'landing_sc'
    grid_1: grid_1
    GridLayout:
        id: grid_1
        cols: 5
        height: 480
        width: 800
        spacing: 25, 20
        padding: 25,25
'''

class MyScreenManager(ScreenManager):
    pass


class LandingScreen(Screen):

    grid_1 = ObjectProperty(None)    #<<<< Propertie

    def __init__(self, **kwargs):
        super(LandingScreen, self).__init__(**kwargs)
        self.buttons = [] # add references to all buttons here
        Clock.schedule_once(self._finish_init)

    def _finish_init(self, dt):
        self.grid_1.cols = 5
        # Loop to make 20 different buttons on screen
        for x in range(15):
            self.buttons.append(Button(text='button{}'.format(x)))
            self.grid_1.add_widget(self.buttons[x])
            self.buttons[x].background_normal = 'star.png'

class MyKivyApp(App):
    def build(self):
        return MyScreenManager()

def main():
    Builder.load_string(kv_text)
    app = MyKivyApp()
    app.run()

if __name__ == '__main__':
    main()