理解Tkinter中的框架类

Question

我是Python新手，试图理解下面的代码。此代码应创建3个框架对象，这些对象可以旋转到前面以交换页面。
APP类应该创建这3个新对象。我不确定是不是。
我尝试的是通过Dashboard类中的函数修改该类上的标签。 i、 e.Dashboard.update（） 有人能解释一下APP类是如何为3个窗口创建框架对象的吗。我现在确定它是，我想我正在尝试更新类中的文本，而不是该类的对象

### Import libaries
import requests
import pyodbc 
import tkinter as tk
from tkinter import *
from tkinter import messagebox, ttk

### Set global fonts
TITLE_FONT = ("Verdana", 12)

### Define the applicaiton class
class APP (Frame):

    ### Build the init function to create the container and windows
    def __init__ (self, master=None ):

        Frame.__init__(self, master)
        self.grid()

        # Set the application window title
        self.master.title("Playing Around with Classes")

        # set the size of the row height for the application
        self.master.rowconfigure(0, weight=1)
        self.master.rowconfigure(1, weight=35)
        self.master.rowconfigure(2, weight=1)
        self.master.rowconfigure(3, weight=1) 

        #Row 0 - Title area
        label = tk.Label(master, text="Playing Around with Classes", font=TITLE_FONT)
        label.grid(row=0, columnspan=3, sticky="nsew")

        # Main presentation are
        Frame2 = Frame(master, bg="#263D42")
        Frame2.grid(row = 1, column = 0, rowspan = 1, columnspan = 3,  sticky = "nsew") 

        # List of pages
        self.frames = {}

        # i think this loop defines the class objects
        for F in (NetworkMap,AuthorPage,Dashboard):

            frame = F(Frame2, self)
            self.frames[F] = frame
            frame.grid(row=0, column=1, sticky="nsew")

        self.show_frame(Dashboard)

    ### Define the show_frame function that will bring the selected fram to the front so it can be viewed
    def show_frame(self, cont):

        frame = self.frames[cont]
        frame.tkraise()

### Create a class for the Dashboard page.  This will also be the start page when the application starts
class Dashboard (tk.Frame):

    def __init__(self, parent, controller):

        tk.Frame.__init__(self,parent, bg="#263D42")
        label = tk.Label(self, text="Text to change", font=TITLE_FONT, bg="#263D42", fg="white", pady = 20)
        label.grid(row=0, column=0, sticky="nsew")

    def update(self):
        self.allPapersLabel.config(text="Changed Text")

### Create a page to get the Author detasil
class AuthorPage (tk.Frame):

    def __init__(self, parent, controller):

        tk.Frame.__init__(self,parent)
        label = tk.Label(self, text="Get Author", font=TITLE_FONT)
        label.grid(row=0, column=0, sticky="nsew")

class NetworkMap (tk.Frame):

    def __init__(self, parent, controller):

        tk.Frame.__init__(self,parent)
        label = tk.Label(self, text="Network Map", font=TITLE_FONT)
        label.grid(row=0, column=0, sticky="nsew")

def changeText():
    Dashboard.update()

changeText()

root = tk.Tk()
root.geometry("600x800+100+100")
app = APP(master=root)
app.mainloop()

Answer 1

Can someone please explain how the APP class is creating frame objects for the 3 windows

关键在于：

for F in (NetworkMap,AuthorPage,Dashboard):
    frame = F(Frame2, self)
    self.frames[F] = frame
    frame.grid(row=0, column=1, sticky="nsew")

请记住NetworkMap、AuthorPage和Dashboard是类。类是可调用的，用作特定类型的新实例的工厂

因此，基本上for循环使F成为每个类的别名（或标签），并依次调用它们来实例化对象

请记住，在大多数语言中我们所称的“变量”在Python中被称为名称。从语言手册：

Names refer to objects. Names are introduced by name binding operations.

所以F只不过是一个方便的标签，用于引用这三个类。for循环头将名称绑定到类

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顺便说一句：这看起来像是一个^{}的重新实现。我建议用它来代替

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编辑

帧被保存到frames字典App对象中。因此，在App实例的所有方法中，您都可以访问self.frames以获得各个帧

有点奇怪（至少对我来说）的是，框架的类对象被用作从字典中进行选择的键

因此，在App的方法中使用self.frames[AuthorPage]应该返回AuthorPage帧