使用函数

Question

从Bryan Oakley给出的答案“在tkinter中切换两帧之间的问题”，我试图在第二页改变按钮的工作方式。

在第一页，使用command=lambda: controller.show_frame(“StartPage”)，它可以正常工作。

在第二页，我想添加一些内容，然后返回但不起作用。

为什么我的回叫没有被调用？

import tkinter as tk                # python 3
from tkinter import font  as tkfont # python 3

class SampleApp(tk.Tk):

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

        self.title_font = tkfont.Font(family='Helvetica', size=18, weight="bold", slant="italic")

        # the container is where we'll stack a bunch of frames
        # on top of each other, then the one we want visible
        # will be raised above the others
        container = tk.Frame(self)
        container.pack(side="top", fill="both", expand=True)
        container.grid_rowconfigure(0, weight=1)
        container.grid_columnconfigure(0, weight=1)

        self.frames = {}
        for F in (StartPage, PageOne, PageTwo):
            page_name = F.__name__
            frame = F(parent=container, controller=self)
            self.frames[page_name] = frame

            # put all of the pages in the same location;
            # the one on the top of the stacking order
            # will be the one that is visible.
            frame.grid(row=0, column=0, sticky="nsew")

        self.show_frame("StartPage")

    def show_frame(self, page_name):
        '''Show a frame for the given page name'''
        frame = self.frames[page_name]
        frame.tkraise()


class StartPage(tk.Frame):

    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        self.controller = controller
        label = tk.Label(self, text="This is the start page", font=controller.title_font)
        label.pack(side="top", fill="x", pady=10)

        button1 = tk.Button(self, text="Go to Page One",
                            command=lambda: controller.show_frame("PageOne"))
        button2 = tk.Button(self, text="Go to Page Two",
                            command=lambda: controller.show_frame("PageTwo"))
        button1.pack()
        button2.pack()


class PageOne(tk.Frame):

    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        self.controller = controller
        label = tk.Label(self, text="This is page 1", font=controller.title_font)
        label.pack(side="top", fill="x", pady=10)
        button = tk.Button(self, text="Go to the start page",
                           command=lambda: controller.show_frame("StartPage"))
        button.pack()


class PageTwo(tk.Frame):

    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        self.controller = controller
        label = tk.Label(self, text="This is page 2", font=controller.title_font)
        label.pack(side="top", fill="x", pady=10)
        button = tk.Button(self, text="Go to the start page",
                           command=self.go_to())
        button.pack()
    def go_to(self):
        # Add something to do            
        self.controller.show_frame("StartPage")


if __name__ == "__main__":
    app = SampleApp()
    app.mainloop()

Answer 1

问题是command的{​​{1}}关键字参数需要一个函数。 您使用Button创建了按钮，因此命令为tk.Button(self, ..., command=self.go_to())，其结果为self.go_to()。

为什么会这样？ None定义如下：

go_to

因此，当Python遇到def go_to(self): # Add something to do self.controller.show_frame("StartPage") 时，它会调用command=self.go_to()，并将返回的值传递给go_to选项。 此值为command（由于缺少None语句而暗示），因此您的命令为return，并且您的按钮无效。

您需要删除括号，因此必须有None。