KivyMD实例化Vkeyboard与MDDropdownMenu及报错处理方案

报错根因及修复点 #

• 第一个ParserException报错是因为KV语法规则错误：VKeyboard的布局属性名是全小写layout，你写了大写开头的Layout，KV中大写开头的标识符会被识别为类声明，属性名必须小写。
• MDDropdownMenu无法显示的两个错误：
  • 类名拼写错误，正确写法是MDDropdownMenu（最后一个M大写）
  • 该组件不能直接作为静态组件放置在屏幕上，需要绑定触发组件（例如按钮），通过回调方法调用open()弹出
• 冗余代码删除：build方法中return screen0之后的代码永远不会执行，可直接删除
• 虚拟键盘无需手动添加：Kivy默认在输入框获焦时自动弹出虚拟键盘，手动添加VKeyboard到界面会导致固定显示冗余键盘，影响交互。如果需要指定数字布局，可通过配置键盘参数实现。

输入获取方法 #

MDTextField的text属性本身就是标准字符串类型，不需要额外做类型转换，后端逻辑直接读取对应id的text属性即可。比如获取用户名输入，代码写法为：

username = self.root.get_screen('menu').ids.username.text

拿到的字符串可直接传入后端逻辑使用。

修复后可运行完整代码 #

from kivymd.app import MDApp
from kivy.lang.builder import Builder
from kivy.uix.screenmanager import Screen, ScreenManager
from kivy.core.window import Window
from kivymd.uix.menu import MDDropdownMenu
Window.size = (300, 500)
Window.keyboard_anim_args = {'d':.2,'t': 'in_out_expo'}
Window.softinput_mode = "below_target"
# 指定虚拟键盘默认布局为数字布局
Window.set_vkeyboard_layout('numeric.json')

screen_helper = """
ScreenManager:
    MenuScreen:
    ProfileScreen:
    UploadScreen:
        

<MenuScreen>:
    name: 'menu'
    
    MDTextField:
        id : username
        hint_text: "Enter Username"
        helper_text: "or click on forgot username"
        helper_text_mode: "on_focus"
        icon_right: "account"
        icon_right_color: app.theme_cls.primary_color
        pos_hint : {'center_x': 0.5, 'center_y': 0.4}
        size_hint_x:None    
        width:250
        mode : "rectangle"
    # 下拉菜单触发按钮
    MDRaisedButton:
        id: menu_btn
        text: "选择城市"
        pos_hint: {'center_x':0.5, 'center_y':0.7}
        on_release: app.menu.open()
    MDRectangleFlatButton:
        text: 'Profile'
        pos_hint: {'center_x':0.5, 'center_y':0.5}
        on_press: root.manager.current = 'profile'
    MDRectangleFlatButton:
        text: 'Upload'
        pos_hint: {'center_x':0.5, 'center_y':0.6}
        on_press: root.manager.current = 'upload'    
<ProfileScreen>:
    name: 'profile'
    MDLabel:
        text: 'Welcome Oliver'
        halign: 'center'
    
    MDRectangleFlatButton:
        text: 'Menu'
        pos_hint: {'center_x':0.5, 'center_y':0.2}
        on_press: root.manager.current = 'menu'    

<UploadScreen>:
    name: 'upload'
    MDLabel:
        text: 'upload daw ek ek'
        halign: 'center'
    
    MDRectangleFlatButton:
        text: 'Menu'
        pos_hint: {'center_x':0.5, 'center_y':0.2}
        on_press: root.manager.current = 'menu'    
                        
"""


class MenuScreen(Screen):
    pass


class ProfileScreen(Screen):
    pass


class UploadScreen(Screen):
    pass


class DemoApp(MDApp):
    def build(self):
        screen0 = Builder.load_string(screen_helper)
        # 初始化下拉菜单
        menu_items = [
            {"text": "Los Angeles", "viewclass": "OneLineListItem", "on_release": lambda x="Los Angeles": self.menu_callback(x)},
            {"text": "Las Vegas", "viewclass": "OneLineListItem", "on_release": lambda x="Las Vegas": self.menu_callback(x)},
            {"text": "New York", "viewclass": "OneLineListItem", "on_release": lambda x="New York": self.menu_callback(x)},
        ]
        self.menu = MDDropdownMenu(
            caller=screen0.get_screen('menu').ids.menu_btn,
            items=menu_items,
            width_mult=4,
        )
        return screen0
    
    # 下拉菜单选择回调
    def menu_callback(self, city):
        print(f"选择的城市是：{city}")
        self.menu.dismiss()
        # 测试获取输入框内容
        username = self.root.get_screen('menu').ids.username.text
        print(f"输入的用户名是：{username}")


DemoApp().run()

内容的提问来源于stack exchange，提问作者Oliver George Almonte