Question

我想在kivy（kv）中做一个非常简单的例子如下：

on_release:
    app.root.ids.scr_mngr.current = 'screen1'

这将失败，因为left_action_items和right_action_items都需要一对对象列表：[name_of_icon，expression]。另一方面，当您处理按钮时，如果我们执行以下操作，该声明将是合法的：

left_action_items: [['arrow-left', lambda x: app.root.ids.scr_mngr.current = 'screen1' ]]

另一方面，left_action_item的正确方法如下：

select *, 
    (Select top 1 BREAK_M 
            from sampleTable 
            where Item_ID <= T.Item_ID 
                and Break_M is not null 
            order by item_ID desc
    ) as LIKETHIS
from sampleTable T
order by item_ID

但这不合法，因为你无法在python下的lambda中执行这样的分配。

left_action_items更改屏幕的方法是什么？

Answer 1

这是我发现单击MDToolbar图标更改屏幕的最简单方法：

main.py

from kivymd.app import MDApp
from kivy.uix.screenmanager import ScreenManager, Screen, NoTransition
from kivy.lang import Builder

Builder.load_file("telas.kv")


class Tela1(Screen):
    pass


class Tela2(Screen):
    pass


class MainApp(MDApp):
    def build(self):
        self.sm = ScreenManager(transition=NoTransition())
        self.sm.add_widget(Tela1(name="tela1"))
        self.sm.add_widget(Tela2(name="tela2"))
        return self.sm

    def change_screen(self, tela):
        self.sm.current = tela

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

telas.kv

<Tela1>:
    BoxLayout:
        orientation: "vertical"
        MDToolbar:
            title: "My App"
        MDRoundFlatButton:
            text: "Go to Tela 2"
            on_release: app.root.current = "tela2"
        MDLabel:
            text: "Tela 1"

<Tela2>:
    BoxLayout:
        orientation: "vertical"
        MDToolbar:
            title: "Tela 2"
            left_action_items: [["arrow-left",  lambda x: app.change_screen("tela1")]]
        MDLabel:
            text: "Tela 2"

Answer 2

你可以将你的根类变成python类，并在那里有一个change_screen方法。还要将您的screenmanager设置为根类中的ObjectProperty 然后在kv中使用partial能够将参数传递给方法试试这样：

from kivy.app import App
from kivy.lang import Builder
from kivy.properties import ObjectProperty
from kivy.uix.boxlayout import BoxLayout
from kivymd.theming import ThemeManager

class MyLayout(BoxLayout):

    scr_mngr = ObjectProperty(None)

    def change_screen(self, screen, *args):
        self.scr_mngr.current = screen


KV = """
#:import Toolbar kivymd.toolbar.Toolbar
#:import partial functools.partial

MyLayout:
    scr_mngr: scr_mngr
    orientation: 'vertical'
    Toolbar:
        id: toolbar
        title: 'My Toolbar'
        left_action_items: [['arrow-left', partial(root.change_screen, 'screen1') ]]
        right_action_items: [['arrow-right', partial(root.change_screen, 'screen2') ]]
    ScreenManager:
        id: scr_mngr
        Screen:
            name: 'screen1'
            Toolbar:
                title: "Screen 1"
        Screen:
            name: 'screen2'
            Toolbar:
                title: "Screen 2"
"""


class MyApp(App):
    theme_cls = ThemeManager()

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


MyApp().run()

Answer 3

有多种选择，你可以做到

left_action_items: [('arrow-left', (app.root.ids.scr_mngr, 'current', 'screen1'))]

以后再做：

for icon, expr in self.left_action_items:
    setattr(*expr)

如果你真的想要一个可执行的表达式，你可以这样做：

left_action_items: [('arrow-left', lambda: setattr(app.root.ids.scr_mngr, 'current' 'screen1'))]

Answer 4

还有另一种方法。我使用的是：

left_action_items: [['arrow-left', lambda x: root.manager.change_screen("main_screen")]]

屏幕管理器内部功能change_screen（）的实现：

def change_screen(self, screen):
    # the same as in .kv: app.root.current = screen
    self.current = screen

Kivy - Kv - ScreenManager - 更改当前屏幕

4 个答案: