Using add_widget in the kv file

I'm having trouble dynamically adding widgets in my kv file, everything I've seen so far has been around adding widgets in the py file. The reason I'd like to use the kv file for this is that I've got a modified Button widget I'd like to use that's written in the kv file and I don't know how to create it in the py file.

So I guess there are two possible questions:

1. How do I use add_widget correctly in the kv file. In the below code I get the NameError: SmoothButton is not defined.

Or

2. How do I create my SmoothButton in the py file?

kv file:

WindowManager:
    ChatPage:

<ChatPage>:
    name: "chat_page"

    NavigationLayout:
        id: nav_layout
        MDNavigationDrawer:
            NavigationDrawerIconButton:
                text: "Test"
                on_release: app.root.current = "login"

        FloatLayout:
            MDToolbar:
                pos_hint: {'top': 1}
                md_bg_color: 0.2, 0.6, 1, 1
                left_action_items: [['menu', lambda x: root.ids.nav_layout.toggle_nav_drawer()]]

            Button:
                text: "Create button"
                pos_hint: {"x": 0.65, "top": 0.15}
                size_hint: 0.35, 0.15
                on_release: root.add_widget(SmoothButton)


<SmoothButton@Button>:
    background_color: 0,0,0,0
    background_normal: ""
    back_color: 1,0,1,1
    border_radius: [6]
    canvas.before:
        Color:
            rgba: self.back_color
        RoundedRectangle:
            size: self.size
            pos: self.pos
            radius: self.border_radius

py file:

import kivy
from kivy.app import App
from kivy.properties import ObjectProperty, StringProperty, NumericProperty, ListProperty
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.lang import Builder
from kivy.uix.popup import Popup
from kivy.uix.label import Label
from kivy.uix.button import Button
from kivy.core.window import Window
from kivymd.theming import ThemeManager
import mysql.connector
from kivymd.uix.picker import MDDatePicker

class ChatPage(Screen):
    pass


class WindowManager(ScreenManager):
    pass


class MyApp(App):
    theme_cls = ThemeManager()

    def build(self):
        kv = Builder.load_file("kivy.kv")
        sm = WindowManager()

        screens = [ChatPage(name="chat_page")]
        for screen in screens:
            sm.add_widget(screen)

        sm.current = "chat_page"
        return sm


if __name__ == '__main__':
    MyApp().run()
Thanks

</details>


# 答案1
**得分**: 2

如果你想在.kv文件中添加修改后的小部件，这并不意味着你必须在那里添加它。解决方案是将修改后的小部件在.kv文件中暴露给.py文件，并在"ChatPage"中创建一个方法，用于添加小部件：

***.py文件***

```python
# ...
class SmoothButton(Button):
    pass

class ChatPage(Screen):
    def on_released(self):
        self.add_widget(SmoothButton())

# ...

.kv文件

# ...
<ChatPage>:
    name: "chat_page"

    NavigationLayout:
        id: nav_layout
        MDNavigationDrawer:
            NavigationDrawerIconButton:
                text: "Test"
                on_release: app.root.current = "login"

        FloatLayout:
            MDToolbar:
                pos_hint: {'top': 1}
                md_bg_color: 0.2, 0.6, 1, 1
                left_action_items: [['menu', lambda x: root.ids.nav_layout.toggle_nav_drawer()]]

            Button:
                text: "Create button"
                pos_hint: {'x': 0.65, 'top': 0.15}
                size_hint: 0.35, 0.15
                on_release: root.on_released()  # <---

<SmoothButton>:  # <---
    background_color: 0, 0, 0, 0
    # ...

请注意，我已经将代码部分从你的原始内容中提取出来，只保留了翻译后的部分。

NavigationLayout:
    id: nav_layout
    MDNavigationDrawer:
        NavigationDrawerIconButton:
            text: "Test"
            on_release: app.root.current = "login"

    FloatLayout:
        MDToolbar:
            pos_hint: {'top': 1}
            md_bg_color: 0.2, 0.6, 1, 1
            left_action_items: [['menu', lambda x: root.ids.nav_layout.toggle_nav_drawer()]]

        Button:
            text: "Create button"
            pos_hint: {"x": 0.65, "top": 0.15}
            size_hint: 0.35, 0.15
            on_release: <b>root.on_released()</b> # <---