Kivy 按下按钮时，会创建一个新按钮，该按钮将进入第二个屏幕

Question

我有一个代码，其中有两个屏幕：“主”和“第二”，当您在主屏幕中按下一个按钮时，会在同一屏幕中创建一个新按钮。我需要创建的新按钮将我带到第二个屏幕。请帮忙，因为我很快就需要它来完成一个更大的项目。

普通代码：

from kivy.app import App
from kivy.uix.button import Button
from kivy.uix.label import Label
from kivy.uix.gridlayout import GridLayout
from kivy.lang import Builder
from kivy.uix.widget import Widget
from kivy.uix.screenmanager import Screen,ScreenManager

class Main(Screen):
   pass
class Second(Screen):
   pass
class Manager(ScreenManager):
   pass
kv=Builder.load_file("test1.kv")
movie=Manager()
movie.add_widget(Main(name="main"))
movie.add_widget(Second(name="second"))

class Movie(App):
   def build(self):
       return movie

Movie().run()

Kv 代码：

#: import Button kivy.uix.button.Button
<Main>:
    name: "main"
    GridLayout:
        id: GL
        cols: 1
        size_hint: (.5,.5)
        pos_hint: {"center_x":.5,"center_y":.5}
        Button:
            text: "Press Me"
            on_press:
                Btn=Button(text="Second",size_hint=(.5,.5),pos_hint= {"center_x":.5,"center_y":.5})
                GL.add_widget(Btn)
                #Btn.bind(on_press= ????)

<Second>:
    name: "second"
    Button:
        text: "Go Back!"
        size_hint: (.5,.5)
        pos_hint: {"center_x":.5,"center_y":.5}
        on_press:
            app.root.current="main"

Answer 1

最简单的方法是在 Main 类中定义一个方法来更改 Screen：

class Main(Screen):
    def switch(self, button_instance):
       self.manager.current = 'second'

然后在kv中引用该方法：

    Button:
        text: "Press Me"
        on_press:
            Btn=Button(text="Second",size_hint=(.5,.5),pos_hint= {"center_x":.5,"center_y":.5}, on_press=root.switch)
            GL.add_widget(Btn)

不需要任何额外方法的更复杂的方法是使用python setattr() 方法设置current Screen 的ScreenManager：

    Button:
        text: "Press Me"
        on_press:
            Btn=Button(text="Second",size_hint=(.5,.5),pos_hint= {"center_x":.5,"center_y":.5})
            Btn.bind(on_press=lambda ins: partial(setattr, root.manager, 'current', 'second')())
            GL.add_widget(Btn)

需要lambda 以避免将Button 实例传递给setattr() 方法。此外，partial 需要在 kv 中导入：

#: import partial functools.partial