为什么不在 init 函数中创建小部件？

Question

我是kivy的新手，所以我正在尝试做一个对我有用的应用程序来学习这个框架。

我需要管理我的轮班工作时间表，所以我开始将日历天插入 GridLayout。经过几次麻烦后，我被阻止了，因为我遇到了这个错误：

File "turno.py", line 53, in load_content    
  self.gridMonthView.add_widget(DaysInfo(day=wid))  
AttributeError: 'NoneType' object has no attribute 'add_widget'

load_content 是从 __init__ 函数内部调用的，当我尝试添加 DaysInfo 小部件（当月的每一天一个）时发生错误。

奇怪的（对我来说）行为是，如果我注释行 n.47（调用 load_content 方法）程序进入运行然后我可以使用 load_content 从内部函数 prevMonth 和 nextMonth 没有任何错误。

所以问题是：

为什么在 __init__ 方法中我不能将 add_widget 用于 gridMonthView reference/object 但它可以从另一个相同的方法 class?
也许无法在 __init__ 函数结束之前添加小部件，而我不会 know/understand?

所以，这是代码：

一个处理日期的小模块：calendario.py

from calendar import Calendar
from datetime import date

IT_months = ['Gennaio', 'Febbraio', 'Marzo', 'Aprile',\
              'Maggio', 'Giugno', 'Luglio', 'Agosto',\
              'Settembre', 'Ottobre', 'Novembre', 'Dicembre']

IT_days = ['Lunedi',
           'Martedi',
           'Mercoledi',
           'Giovedi',
           'Venerdi',
           'Sabato',
           'Domenica']


class Calendario():

    def __init__ (self):

        self.currDay = date.today()
        self.calen = Calendar(0)
        # def __init__ (self):

    def getMonth(self):
        return IT_months[self.currDay.month-1]
        # def getMonth(self):

    def getYear(self):
        return str(self.currDay.year)
        # def getYear(self):

    def getDaysOfMonth(self, listOfDays):
        listOfDays = []
        for td in self.calen.itermonthdates(self.currDay.year, self.currDay.month):
            listOfDays.append(td.day)
            # for td in ...

        return listOfDays
        # def getDaysOfMonth(self, listOfDays):

    def setNextMonth(self):
        if self.currDay.month == 12:
            self.currDay = self.currDay.replace(month=1, year=(self.currDay.year+1))
        else:
            self.currDay = self.currDay.replace(month=(self.currDay.month+1))
        # def setNextMonth(self):

    def setPrevMonth(self):
        if self.currDay.month == 1:
            self.currDay = self.currDay.replace(month=12, year=(self.currDay.year-1))
        else:
            self.currDay = self.currDay.replace(month=(self.currDay.month-1))
        # def setNextMonth(self):

.kv 文件：turno.kv

#:kivy 1.9.0
# 
# menu bar
#
<MenuBar>:
    orientation: 'horizontal'
    padding: 1
    spacing: 1
    size_hint_y: 0.15
    Button:
        text: "Icon"
        size_hint_x: 0.3
        on_press: root.menu()
    Button:
        text: "Title"
        #size_hint: 1, 0.5


#
# day's info 
#
<DaysInfo>:
    orientation: 'vertical'
    padding: 1
    spacing: 1
    Label:
        color: 1,0,0,1
        background_color: 1,1,1,1
        id: f1
        text: " "
    Label:
        id: f2
        text: " "
    Label:
        id: f3
        text: " "


#
# month view
#
<MonthView>:
    gridMonthView: gridMonthView
    #
    orientation: "vertical"
    #
    # month selection
    #
    BoxLayout:
        id: box1
        orientation: 'horizontal'
        padding: 1
        spacing: 1
        size_hint_y: 0.15
        Button:
            backgroud_color: 0,1,0,1
            text: " << "
            size_hint_x: 0.1
            on_press: root.prevMonth()
        Button:
            id: idSelMonth
            text: root.curMonth
            size_hint_x: 0.5
        Button:
            id: isSelYear
            text: root.curYear
            size_hint_x: 0.3
        Button:
            text: " >> "
            size_hint_x: 0.1
            on_press: root.nextMonth()
    #
    # week's days
    #
    BoxLayout:
        id: box2
        orientation: 'horizontal'
        padding: 1
        spacing: 1
        color: 0., 0.5, 0.5, 1
        size_hint_y: 0.1
        Label:
            text: "Lu"
        Label:
            text: "Ma"
        Label:
            text: "Me"
        Label:
            text: "Gi"
        Label:
            text: "Ve"
        Label:
            text: "Sa"
        Label:
            text: "Do"
    #
    # Month's days
    #
    GridLayout:
        id: gridMonthView
        cols: 7
        rows: 6
        padding: 1
        spacing: 1
        size_hint_y: 0.6

#
# Turno Main Form
#
<TurnoMainForm>:
    orientation: 'vertical'
    padding: 20
    spacing: 10
    #width: 400
    #height: 800

    # menu bar
    MenuBar:

    # month view
    MonthView:
        id: id1

应用程序的源代码：turno.py

# -*- coding: utf-8 -*-
"""
Created on Mon Oct 06 12:25:04 2015

@author: a809077
"""

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.gridlayout import GridLayout
from kivy.properties import ObjectProperty, StringProperty
from kivy.config import Config

from calendario import Calendario

# impostazione della grandezza della finestra
Config.set('graphics', 'width', '480')
Config.set('graphics', 'height', '800')

class MenuBar(BoxLayout):

    def __init__(self, **kwargs):
        super(MenuBar, self).__init__(**kwargs)
        print ("------- MenuBar -------")
        for child in self.children:
            print(child)

    def menu (self):
        print (" ====== click sul menu ======")
    # end of class: MenuBar(BoxLayout)

##
## visualizza i dati mensili    
##
class MonthView(BoxLayout):

    gridMonthView = ObjectProperty(None)

    curMonth = StringProperty()
    curYear = StringProperty()

    def __init__(self, **kwargs):
        print ("------- Month View -------")
        self.curMonth = TurnoApp.currCal.getMonth()
        self.curYear = TurnoApp.currCal.getYear()
        super(MonthView, self).__init__(**kwargs)
        self.load_content(True)
        self.printInfo()

    def load_content(self, clearWidget = False):
        if (clearWidget):
            print "---- Clear Widgets ----"
            self.gridMonthView.clear_widgets()

        lod = list ()
        lod = TurnoApp.currCal.getDaysOfMonth(lod)
        for wid in lod:
            self.gridMonthView.add_widget(DaysInfo(day=wid))

    def prevMonth (self):
        print (" ====== click sul mese precedente 1 ======")
        TurnoApp.currCal.setPrevMonth()
        self.curMonth = TurnoApp.currCal.getMonth()
        self.curYear = TurnoApp.currCal.getYear()
        #self.printInfo()
        self.load_content(True)

    def nextMonth (self):
        print (" ====== click sul mese successivo ======")
        TurnoApp.currCal.setNextMonth()
        self.curMonth = TurnoApp.currCal.getMonth()
        self.curYear = TurnoApp.currCal.getYear()
        #self.printInfo()
        self.load_content(True)

    def printInfo (self):
        print " ____ items ____"
        for key, val in self.ids.items():
            print("key={0}, val={1}".format(key, val))
        print " ____ childs ____"
        for child in self.children:
            print("{} -> {}".format(child, child.id))
        print " ____ walk ____"
        for obj in self.walk():
            print obj
    # end of class: MonthView(GridLayout):


class DaysInfo(BoxLayout):
     def __init__(self, **kwargs):
        super(DaysInfo, self).__init__()
        #print ("-- Days Info - {:d} ------".format(kwargs["day"]))
        self.ids["f1"].text =str(kwargs["day"])       
    # end of class: DaysInfo(BoxLayout):


class TurnoMainForm(BoxLayout):

    def __init__(self, **kwargs):
        super(TurnoMainForm, self).__init__(**kwargs)
        print ("-------TurnoMainForm-------")
        for child in self.children:
            print(child)
    # end of class: TurnoMainForm(BoxLayout):


class TurnoApp (App):
    # icon = 'mia_icona.png'
    title = 'Turno Terna'
    currCal = Calendario()

    def build (self):
        return TurnoMainForm()
        #return MonthView()

    # end of class: TurnoApp (App):


TurnoApp().run()

我不会尝试将代码缩减为示例，而是 post 一切，因为这样可能更好地理解问题出在哪里，并给我一些改进代码的提示。

Answer 1

Why does it seem that inside the init method I can't use add_widget for gridMonthView reference/object but it's possible from the other methods of the same class?

因为 self.gridMonthView 还没有在 __init__ 中设置（即从默认值 None 修改）。这是一个技术限制 - 想象两个具有 kv 规则的小部件相互引用，在这种情况下，至少其中一个不能在其 __init__ 中引用另一个，因为它将是第一个实际实例化的小部件.这就是您在这里看到的那种效果，必须先实例化所有小部件，然后才能设置它们之间的引用。

它适用于其他方法，因为您只能稍后调用它们，在所有实例化完成之后。

您可以使用 Clock.schedule_once(self.post_init, 0) 之类的东西，并将您的小部件添加到 post_init 方法中；间隔为 0 的调度确保它会在下一帧之前发生，但在当前正在进行的所有事情都完成之后。

为什么不在 init 函数中创建小部件？

Why are widgets not created at init function?

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为什么不在 __init__ 函数中创建小部件？

Why are widgets not created at __init__ function?

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为什么不在 init 函数中创建小部件？

Why are widgets not created at init function?