python - OOP tkinter : How to set focus (and add text) to entry?

Question

重构工作过程代码后，我无法集中精力工作。因为它在我可能把类(class)弄乱之前就起作用了。

import tkinter as tk
from tkinter import ttk

LARGE_FONT = ("Verdana", 14)
ANSWER_FONT = ("Verdana", 20, "bold")

class myApp(tk.Tk):

    def __init__(self, *args, **kwargs):

        tk.Tk.__init__(self, *args, **kwargs)

        container = ttk.Frame(self)
        container.pack(side=tk.TOP, fill=tk.BOTH, expand=True)
        container.grid_rowconfigure(0, weight=1)
        container.grid_columnconfigure(0, weight=1)

        self.frames = {}
        for F in [StartPage, PageOne]:
            frame = F(container, self)
            self.frames[F] = frame
            frame.grid(row=0, column=0, sticky="nsew")

        self.show_frame(StartPage)

    def show_frame(self, cont):

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


class StartPage(ttk.Frame):

    def __init__(self, parent, controller):

        ttk.Frame.__init__(self, parent)

        label = ttk.Label(self, text="StartPage", font=LARGE_FONT)
        label.pack(padx=10, pady=10)

        but_1 = ttk.Button(self, text="Page 1",
                            command=lambda: controller.show_frame(PageOne))
        but_1.pack(padx=10, pady=10)


class PageOne(ttk.Frame):

    def __init__(self, parent, controller):

        ttk.Frame.__init__(self, parent)

        label = ttk.Label(self, text="Page One", font=LARGE_FONT)
        label.pack(pady=10, padx=10)

        frame_answ = ttk.Frame(self)
        frame_answ.pack(side=tk.TOP, fill=tk.X)

        useranswer = tk.StringVar()
        entry_answ = ttk.Entry(self, textvariable=useranswer, font=ANSWER_FONT, justify=tk.CENTER)
        entry_answ.pack(fill=tk.X)

        useranswer.set("a default value")        ##  These two lines
        entry_answ.focus_set()                   ##  just won\'t work

        frame_button = ttk.Frame(self)
        frame_button.pack(padx=10, pady=10)
        but_next = ttk.Button(frame_button, text="back", state=tk.NORMAL,
                                command=lambda: controller.show_frame(StartPage))
        but_next.pack(side=tk.LEFT)


app = myApp()
app.geometry("300x150+300+300")
app.mainloop()

我的目标:点击“第 1 页”按钮后，焦点应该在条目上(并且文本“默认值”应该显示在其中)。

Answer 1

问题是您在 myApp 类中初始化了 StartPage 和 PageOne。

因此，PageOne 的__init__ 方法在框架激活之前被初始化。

解决方案是在 PageOne 中创建一个新方法来设置焦点和文本变量，只有当您单击 PageOne 按钮时，您才会调用该设置方法。

这是代码:

import tkinter as tk
from tkinter import ttk

LARGE_FONT = ("Verdana", 14)
ANSWER_FONT = ("Verdana", 20, "bold")

class myApp(tk.Tk):

    def __init__(self, *args, **kwargs):

        tk.Tk.__init__(self, *args, **kwargs)

        container = ttk.Frame(self)
        container.pack(side=tk.TOP, fill=tk.BOTH, expand=True)
        container.grid_rowconfigure(0, weight=1)
        container.grid_columnconfigure(0, weight=1)

        self.frames = {}
        for F in [StartPage, PageOne]:
            frame = F(container, self)
            self.frames[F] = frame
            frame.grid(row=0, column=0, sticky="nsew")

        self.show_frame(StartPage)

    def show_frame(self, cont):
        frame = self.frames[cont]
        frame.tkraise()


class StartPage(ttk.Frame):

    def __init__(self, parent, controller):

        ttk.Frame.__init__(self, parent)
        self.controller = controller
        label = ttk.Label(self, text="StartPage", font=LARGE_FONT)
        label.pack(padx=10, pady=10)

        but_1 = ttk.Button(self, text="Page 1",
                            command=self.page_one_command)
        but_1.pack(padx=10, pady=10)

    def page_one_command(self):
        self.controller.show_frame(PageOne)
        self.controller.frames[PageOne].set_unanswer()  # Only after calling the show_frame you call the set method that will set the focus and the textvariable.


class PageOne(ttk.Frame):

    def __init__(self, parent, controller):

        ttk.Frame.__init__(self, parent)

        label = ttk.Label(self, text="Page One", font=LARGE_FONT)
        label.pack(pady=10, padx=10)

        frame_answ = ttk.Frame(self)
        frame_answ.pack(side=tk.TOP, fill=tk.X)

        self.useranswer = tk.StringVar()
        self.entry_answ = ttk.Entry(self, textvariable=self.useranswer, font=ANSWER_FONT, justify=tk.CENTER)
        self.entry_answ.pack(fill=tk.X)

        frame_button = ttk.Frame(self)
        frame_button.pack(padx=10, pady=10)
        but_next = ttk.Button(frame_button, text="back", state=tk.NORMAL,
                                command=lambda: controller.show_frame(StartPage))
        but_next.pack(side=tk.LEFT)

    def set_unanswer(self):
        self.useranswer.set("a default value")        
        self.entry_answ.focus_set()                   


app = myApp()
app.geometry("300x150+300+300")
app.mainloop()