Python Tkinter类中按钮绑定回车键失效问题求助

问题描述 #

刚学习Tkinter，尝试为按钮绑定回车键（Enter）但始终无法生效：

• 直接绑定按钮：Enter.bind('<Return>', lambda:self.retrieve_Input(t))
• 绑定到自身：self.bind('<Return>', lambda:self.retrieve_Input(t))
  只有移除lambda才能触发，但不符合需求。以下是完整代码：

import sys
import tkinter as tk
from tkinter import ttk

class windows(tk.Tk):
    def __init__(self, *args, **kwargs):
        tk.Tk.__init__(self, *args, **kwargs)
        self.wm_title("Test Application")
        self.lift() #Bringing the GUI to the front of the screen
        main_frame = tk.Frame(self, height=400, width=600) #Creating a main Frame for all pages
        main_frame.pack(side="top", fill="both", expand=True)
        main_frame.grid_rowconfigure(0, weight=1) #Configuring the location of the main frame using grid
        main_frame.grid_columnconfigure(0, weight=1)

        # We will now create a dictionary of frames
        self.frames = {}
        for F in (MainPage, CompletionScreen): #Add the page components to the dictionary.
            page = F(main_frame, self)
            self.frames[F] = page #The windows class acts as the root window for the frames.
            page.grid(row=0, column=0, sticky="nsew")
        self.show_page(MainPage) #Method to switch Pages

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

##########################################################################

class MainPage(tk.Frame):
    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)

        tk.Label(self, text="Project Python Search Engine", bg='white').pack()
        tk.Label(self, text="", bg='white').pack()
        tk.Label(self, text="Song", bg='white').pack()
        tk.Label(self, text="", bg='white').pack()
        t = tk.Entry(self, bg='white', width = 50)
        t.pack()
        tk.Label(self, text="", bg='white').pack()
        Enter = tk.Button(self, text='Search', command= lambda:self.retrieve_Input(t))
        Enter.pack()
        tk.Button(self, text="Latest Popular Songs", command=lambda:self.Popular_Songs(t)).pack() #Line 210 onwards

        Enter.bind('<Return>', lambda:self.retrieve_Input(t))

    def retrieve_Input(self, t):
        print ("work")
        print (t)

class CompletionScreen(tk.Frame):
    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        label = tk.Label(self, text="Completion Screen, we did it!")
        label.pack(padx=10, pady=10)
        switch_window_button = ttk.Button(
            self, text="Return to menu", command=lambda: controller.show_page(MainPage)
        )
        switch_window_button.pack(side="bottom", fill=tk.X)

if __name__ == "__main__":
    App = windows()
    App.mainloop()

问题原因及解决方法 #

• 原因：按钮未获得键盘焦点，只有控件获得焦点时，绑定在该控件上的键盘事件才会触发。用户输入内容时，焦点通常在输入框（Entry）上，而非按钮，因此绑定在按钮上的回车键事件无法触发。
• 解决方法：将回车键绑定设置在输入框（Entry）上，因为输入框是用户交互时默认获得焦点的控件。同时注意，键盘事件的回调函数默认会接收一个event参数，lambda需要包含该参数避免报错。

修改MainPage类中的绑定代码，将原来绑定按钮的语句替换为：

t.bind('<Return>', lambda event: self.retrieve_Input(t))

内容的提问来源于stack exchange，提问作者Dylan Thomas