Kivy：访问列表对象时发生属性错误：'NoneType' 对象没有属性 'bind'

Question

我正在构建一个多屏幕Kivy应用程序。其中一个屏幕构建了一个列表，我将传递给其他函数，这些函数将在另一个屏幕上显示结果。py文件中的一个屏幕包含get_items（）方法：

class Menu(Screen):
    def get_items(self):
        return self._items

self.\u items是一个列表，它还根据类中的用户操作进行初始化和修改。所有这些工作，我可以打印自己的项目在终端。但是，我需要做的是把这个列表传递到另一个屏幕上，我实现了这一点，我把自己变成了一个可以在应用程序中的任何地方访问的列表（我在菜单屏幕上有一个按钮，按下时可以执行此操作）：

^{pr2}$

所以我认为发生的是，我已经将列表self.\u项分配给了一个对象应用程序项列表通过函数get_items（）。我已经证实了这一点应用程序项列表实际上仍然是一个列表，我可以通过其他屏幕将它及其长度打印到终端。但是，我不能，例如，使它成为标签的文本，即使我将其转换为字符串。例如

Button:
    text: str(app.itemlist)

返回错误'NoneType' object has no attribute 'bind'。如果我把itemlist传递给一个返回字符串的函数（这是我最终想要做的），我会得到相同的错误。我已经在这件事上耽搁了很长一段时间了，如果有任何帮助，我将不胜感激。在

编辑

在主.py公司名称：

import kivy
kivy.require('1.10.0')

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.button import Button
from kivy.uix.label import Label
from kivy.uix.scrollview import ScrollView
from kivy.uix.gridlayout import GridLayout
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.textinput import TextInput
from kivy.uix.screenmanager import ScreenManager, Screen
from snartoolsmod import *

Builder.load_file("snartools.kv")

class DiningButton(Button):
    pass

class DirectionButton(Button):
    pass

class ItemButton(Button):
    pass

class SubmenuButton(Button):
    pass

class HomeScreen(Screen):
    pass

class WhitmansMenu(Screen):

    def initialize_list(self):
        itemList = Menu('whitmans')
        global allItems
        allItems = itemList.getCopy()
        return itemList

    def modify_list(self, itemList, value, dish):
        if value == 'down':
            for item in itemList:
                if dish == item.getDish():
                    itemList.remove(item)
                    break
        else:
            for item in allItems:
                if dish == item.getDish():
                    itemList.append(item)
                    break

    def modify_state(self, value, submenu, length):
        if value == 'down':
            for i in range(1, length+1):
                button = self.ids[str(submenu)+'_item'+str(i)]
                button.state = 'down'
        else:
            for i in range(1, length+1):
                button = self.ids[str(submenu)+'_item'+str(i)]
                button.state = 'normal'

class ToolScreen(Screen):
    pass

class ToolButton(Button):
    pass

class InstructionsLabel(Label):
    pass

class SubLabel(Label):
    pass

class LengthExact(Screen):

    def get_list(self, itemList):
        return itemList

class LengthRange(Screen):
    pass

class PriceExact(Screen):
    pass

class PriceRange(Screen):
    pass

class MoreExact(Screen):
    pass

class MoreRange(Screen):
    pass

screen_manager = ScreenManager()
screen_manager.add_widget(HomeScreen(name="home_screen"))
screen_manager.add_widget(WhitmansMenu(name="whitmans_menu"))
screen_manager.add_widget(ToolScreen(name="tool_screen"))
screen_manager.add_widget(LengthExact(name="length_exact"))
screen_manager.add_widget(LengthRange(name="length_range"))
screen_manager.add_widget(PriceExact(name="price_exact"))
screen_manager.add_widget(PriceRange(name="price_range"))
screen_manager.add_widget(MoreExact(name="more_exact"))
screen_manager.add_widget(MoreRange(name="more_range"))

class SnartoolsApp(App):

    def build(self):
        return screen_manager

app = SnartoolsApp()
app.run()

.kv文件（只是基本部分-相当长）：

<WhitmansMenu>:
    on_enter: app.itemList = root.initialize_list()
    canvas.before:
        Color:
            rgba: 1, 1, 1, 1
        Rectangle:
            pos: self.pos
            size: self.size
    FloatLayout:
        DirectionButton:
            text: "Back"
            pos_hint: {'left': 1, 'top': 1}
            on_press:
                root.manager.transition.duration = 0
                root.manager.current = "home_screen"
        DirectionButton:
            text: "Done"
            pos_hint: {'right': 1, 'top': 1}
            on_press:
                root.manager.transition.duration = 0
                root.manager.current = "tool_screen"
    BoxLayout:
        orientation: "vertical"
        pos_hint: {'top': 0.86}
        InstructionsLabel:
            text: "Select all menus and items to exclude from your order"
        ScrollView:
            GridLayout:
                cols: 1
                padding: 20
                spacing: 5
                size_hint_y: None
                height: self.minimum_height
                SubmenuButton:
                    id: fryer
                    text: 'Fryer'
                    on_state: root.modify_state(fryer.state, 'fryer', 7)
                ItemButton:
                    id: fryer_item1
                    text: 'Fried Green Beans'
                    on_state: root.modify_list(app.itemList, fryer_item1.state, 'Fried Green Beans')
                # A bunch more buttons below...
<LengthExact>:
    canvas.before:
        Color:
            rgba: 1, 1, 1, 1
        Rectangle:
            pos: self.pos
            size: self.size
    FloatLayout:
        DirectionButton:
            text: "Back"
            pos_hint: {'left': 1, 'top': 1}
            on_press:
                root.manager.transition.duration = 0
                root.manager.current = "tool_screen"
    GridLayout:
        cols: 1
        pos_hint: {'top': 0.86}
        BoxLayout:
            orientation: "vertical"
            InstructionsLabel:
                text: "Enter the number of items you want to order"
            SubLabel:
                text: root.get_list(str(app.itemList))

上面看到的Item和Menu类是在另一个.py文件中定义的：

class Item(object):
    __slots__ = ["_canteen", "_submenu", "_dish", "_price"]

    def __init__(self, canteen, submenu, dish, price):
        self._canteen = canteen
        self._submenu = submenu
        self._dish = dish
        self._price = float(price)

    def getCanteen(self):
        return self._canteen

    def getSubmenu(self):
        return self._submenu

    def getDish(self):
        return self._dish

    def getPrice(self):
        return self._price

    def __len__(self):
        return 1

    def __eq__(self, other):
        return (self._dish == other._dish) and \
               (self._price == other._price)

    def __repr__(self):
        return "Item({0},{1},{2},{3})".format(self._canteen, self._submenu, self._dish, self._price)

    def __str__(self):
        return "<{0},{1},{2},{3}>".format(self._canteen, self._submenu, self._dish, self._price)


class Menu(object):
    __slots__ = ["_canteen", "_result"]

    def __init__(self, canteen):
        self._canteen = canteen
        self._result = []
        with open(self._canteen + '.csv', 'r') as f:
            csvr = csv.reader(f)
            for row in csvr:
                item = Item(row[0], row[1], row[2], row[3])
                self._result.append(item)

    def getCanteen(self):
        return self._canteen

    def getSubmenus(self):
        submenus = []
        for item in self._result:
            if item._submenu not in submenus:
                submenus.append(item._submenu)
        return submenus

    def getDishes(self):
        dishes = []
        for item in self._result:
            dishes.append(item._dish)
        return dishes

    def getPrices(self):
        prices = []
        for item in self._result:
            if item._price not in prices:
                prices.append(item._price)
        return prices

    def specifySubmenus(self, submenus):
        items = []
        for item in self._result:
            if item._submenu in submenus:
                items.append(item)
        self._result = items

    def sortMenu(self):
        return sorted(self._result, key=lambda x: x._price)

    def longestOrder(self, price):
        sortedMenu = self.sortMenu()
        minPrice = sortedMenu[0]._price
        return int(price / minPrice)

    def shortestOrder(self, price):
        sortedMenu = self.sortMenu()
        maxPrice = sortedMenu[-1]._price
        return int(price / maxPrice)

    def longOrder(self, price, sortedMenu=None):
        if sortedMenu == None:
            sortedMenu = self.sortMenu()
        sum = 0
        order = []
        for item in sortedMenu:
            if sum + item._price <= price:
                order.append(item._dish)
                sum += item._price
        return order

    def lengthExact(self, length):
        orders = []
        maxLen = len(self.longOrder(7))
        assert length == int(length) and 0 < length <= maxLen
        sortedMenu = self.sortMenu()
        maxPrice = 7 - (length - 1) * sortedMenu[0]._price
        for item in sortedMenu:
            if item._price > maxPrice:
                sortedMenu.remove(item)
        allCombos = list(itertools.combinations_with_replacement(sortedMenu, length))
        for combo in allCombos:
            sum = 0
            for item in combo:
                sum += item._price
            if sum <= 7:
                orders.append(combo)
        return orders

    def lengthRange(self, lower, upper):
        allCombos = []
        orders = []
        maxLen = self.longestOrder(7)
        assert lower == int(lower) and upper == int(upper) and 0 < lower < upper <= maxLen
        sortedMenu = self.sortMenu()
        for i in range(lower, upper + 1):
            maxPrice = 7 - (i - 1) * sortedMenu[0]._price
            for item in sortedMenu:
                if item._price > maxPrice:
                    sortedMenu.remove(item)
            allCombos += list(itertools.combinations_with_replacement(sortedMenu, i))
        for combo in allCombos:
            sum = 0
            for item in combo:
                sum += item._price
            if sum <= 7:
                orders.append(combo)
        return orders

    def priceExact(self, price):
        allCombos = []
        orders = []
        assert 0 < price <= 7
        sortedMenu = self.sortMenu()
        cheapestPrice = sortedMenu[0]._price
        maxLen = self.longestOrder(price)
        minLen = self.shortestOrder(price)
        for i in range(minLen, maxLen + 1):
            if i == 1:
                for item in self._result:
                    if item._price == price:
                        sortedMenu.remove(item)
            else:
                maxPrice = price - (i - 1) * cheapestPrice
                for item in sortedMenu:
                    if item._price > maxPrice:
                        sortedMenu.remove(item)
                allCombos += list(itertools.combinations_with_replacement(sortedMenu, i))
        for combo in allCombos:
            sum = 0
            for item in combo:
                sum += item._price
            if sum == price:
                orders.append(combo)
        return orders

    def priceRange(self, lower, upper):
        allCombos = []
        orders = []
        assert 0 < lower <= upper <= 7
        sortedMenu = self.sortMenu()
        cheapestPrice = sortedMenu[0]._price
        maxLen = self.longestOrder(upper)
        minLen = self.shortestOrder(upper)
        for i in range(minLen, maxLen + 1):
            if i == 1:
                for item in self._result:
                    if item._price >= lower and item._price <= upper:
                        orders.append(item)
            else:
                maxPrice = upper - (i - 1) * cheapestPrice
                for item in sortedMenu:
                    if item._price > maxPrice:
                        sortedMenu.remove(item)
                allCombos += list(itertools.combinations_with_replacement(sortedMenu, i))
        for combo in allCombos:
            sum = 0
            for item in combo:
                sum += item._price
            if sum >= lower and sum <= upper:
                orders.append(combo)
        return orders

    def moreExact(self, order, price):
        orderPrice = 0
        for item in self._result:
            if item._dish in order:
                orderPrice += item._price
        assert orderPrice <= price <= 7
        remaining = price - orderPrice
        return self.priceExact(remaining)

    def moreRange(self, order, lower, upper):
        orderPrice = 0
        for item in self._result:
            if item._dish in order:
                orderPrice += item._price
        assert lower < upper <= 7 and orderPrice < upper
        low = lower - orderPrice
        high = upper - orderPrice
        return self.priceRange(low, high)

    def append(self, value):
        return self._result.append(value)

    def remove(self, value):
        return self._result.remove(value)

    def getCopy(self):
        return self._result.copy()

    def __iter__(self):
        return iter(self._result)

    def __len__(self):
        return len(self._result)

    def __repr__(self):
        return "Menu({})".format(self._result)

    def __str__(self):
        return "{}".format(self._result)

Answer 1

好吧，这似乎有效： https://pastebin.com/A2hEKHLx

当kivy试图从.kv文件自动获取你的应用程序时，它使用App.get_running_app()函数。由于某种原因，它没有返回任何结果。我是在LengthExact类中手动完成的，看看。我还为itemList添加了一个默认值[]。在