第一个 Python/Kivy/KivyMD 应用程序。无法将文本字段中的数据保存到变量 + 数据绑定到 MDList

Posted 2023-04-14

【中文标题】第一个 Python/Kivy/KivyMD 应用程序。无法将文本字段中的数据保存到变量 + 数据绑定到 MDList

【英文标题】：First Python/Kivy/KivyMD App. Unable to save data from textfield to variable + data binding to MDList

【发布时间】：2021-04-15 08:48:06

【问题描述】：

我最近开始在 python/kivy 中开发一个学校上交应用程序。 我处于我在 kivymd 和用户类中创建和 UI 的状态。 我想将信息保存到用户对象列表中，但 我收到 KeyError: 'firstname' 错误消息。 你们知道可能是什么问题吗？

我还想实现的是，我将 MDList 放到第二个屏幕上。使用数据绑定，我想显示列表中用户的名字和姓氏。知道我怎样才能做到这一点吗？我没有在网上找到可用的解决方案。

提前感谢您的帮助！

from kivymd.app import MDApp
from kivy.lang.builder import Builder
from kivy.uix.screenmanager import Screen, ScreenManager
from kivy.uix.textinput import _textinput_list

screen_helper = """
ScreenManager:
    id: smn
    AddUserScreen:
    ViewListScreen:
    ModifyUser:
    
<AddUserScreen>:
    id: screen1
    name: 'adduser'
    MDTextField:
        id:firstname
        hint_text: "First Name"
        helper_text: "Please enter your firts name"
        helper_text_mode: "on_focus"
        pos_hint: 'center_x': 0.5, 'center_y': 0.9
        size_hint_x: None
        width:300
    MDTextField:
        id: lastname
        hint_text: "Last Name"
        helper_text: "Please enter your last name"
        helper_text_mode: "on_focus"
        pos_hint: 'center_x': 0.5, 'center_y': 0.8
        size_hint_x: None
        width:300
    MDTextField:
        id: city
        hint_text: "City of Residence"
        helper_text: "Please enter your city of residence"
        helper_text_mode: "on_focus"
        pos_hint: 'center_x': 0.5, 'center_y': 0.7
        size_hint_x: None
        width:300 
    MDTextField:
        id: year
        hint_text: "Birthyear"
        helper_text: "Please enter your birthyear"
        helper_text_mode: "on_focus"
        pos_hint: 'center_x': 0.5, 'center_y': 0.6
        size_hint_x: None
        width:300               
    MDRectangleFlatButton:
        text: 'View User List'
        pos_hint: 'center_x': 0.7, 'center_y': 0.1
        on_press: root.manager.current = 'viewlists'        
    MDRectangleFlatButton:
        text: 'Add User'
        pos_hint: 'center_x': 0.3, 'center_y': 0.1
        on_press: root.addUser()
        
        
<ViewListScreen>:
    id: screen2
    name: 'viewlists'
    MDList:
        id: container
        pos_hint: 'center_x': 0.5, 'center_y': 0.9
    MDRectangleFlatButton:
        text: 'Add New User'
        pos_hint: 'center_x': 0.3, 'center_y': 0.1
        on_press: root.manager.current = 'adduser'       
    MDRectangleFlatButton:
        text: 'Modify User'
        pos_hint: 'center_x': 0.7, 'center_y': 0.1
        on_press: root.manager.current = 'modify'

<ModifyUser>:
    id: 'screen3"
    name: 'modify'
    MDRectangleFlatButton:
        text: 'Add New User'
        pos_hint: 'center_x': 0.3, 'center_y': 0.1
        on_press: root.manager.current = 'adduser'       
    MDRectangleFlatButton:
        text: 'View User'
        pos_hint: 'center_x': 0.7, 'center_y': 0.1
        on_press: root.manager.current = 'viewlists'
        
"""


class AddUserScreen(Screen):
    def addUser(self):
        screen1_instance = sm.get_screen('adduser')
        firstname1 = screen1_instance.ids['firstname'].text
        lastname1 = screen1_instance.ids['lastname'].text
        city1 = screen1_instance.ids['city'].text
        year1 = screen1_instance.ids['year'].text
        userlist.append(User(firstname1, lastname1, city1, year1))
        print('New User Added')


class ViewListScreen(Screen):
    pass


class ModifyUser(Screen):
    pass


userlist = []
sm = ScreenManager()
sm.add_widget(AddUserScreen(name='adduser'))
sm.add_widget(ViewListScreen(name='viewlists'))
sm.add_widget(ModifyUser(name='modify'))


class App(MDApp):

    def build(self):
        screen = Builder.load_string(screen_helper)
        return screen


App().run()


class User:
    def __init__(self, firstname, lastname, country, year):
        self.firstname = firstname
        self.lastname = lastname
        self.country = country
        self.year = year

【参考方案1】：

您的代码存在一些问题。一、台词：

sm = ScreenManager()
sm.add_widget(AddUserScreen(name='adduser'))
sm.add_widget(ViewListScreen(name='viewlists'))
sm.add_widget(ModifyUser(name='modify'))

正在构建您的App 中未使用的小部件树。这些行可以删除。

其次，User 类定义出现在App().run() 之后，这意味着正在运行的App 没有该类可用。这个类定义应该移到App().run()之前

第三，addUser() 方法使用上面定义的sm，它不属于您的App 小部件树，尚未显示，因此没有ids（导致错误）。对addUser() 方法的更正访问App 的实际小部件树。像这样：

class AddUserScreen(Screen):
    def addUser(self):
        screen1_instance = self.manager.get_screen('adduser')  # get correct Screen
        firstname1 = screen1_instance.ids['firstname'].text
        lastname1 = screen1_instance.ids['lastname'].text
        city1 = screen1_instance.ids['city'].text
        year1 = screen1_instance.ids['year'].text
        userlist.append(User(firstname1, lastname1, city1, year1))
        print('New User Added')

另外，将App 命名为App 可能是个坏主意，因为App 是MDApp 的基类的名称。一个更好的主意是选择一个唯一的名称。