Tkinter单选按钮与复选框无法更新变量值问题求助

问题现象 #

用Tkinter开发GUI时，通过类方法创建弹窗窗口，弹窗包含目录选择按钮、一对单选按钮（RadioG、RadioY）和一个复选框（state_checkbox），预期实现：

• 单选按钮切换更新driveletter变量
• 复选框勾选/取消更新statevalue变量

实际出现异常：

• driveletter初始设为“G:”有效，但选择“Y:”单选按钮时变量值不更新
• statevalue通过IntVar.set(1)设置初始值，复选框未默认勾选，且勾选/取消时值始终为1，不会变为0

问题代码 #

class preferences(Preferences):
    def save_preferences(self):
        # Used to reset the folder location desired by the user
        self.prefdialog = tk.Tk()
        self.prefdialog.title('Set Preferences')

        self.driveletter = tk.StringVar()
        self.driveletter.set("G:")
        self.statevalue = tk.IntVar()
        self.statevalue.set(1)
        self.fpath = '\Desktop'

        self.RadioG = tk.Radiobutton(self.prefdialog, text="G:", variable=self.driveletter,
            value="G:", command=lambda: print(self.driveletter.get()))
        self.RadioG.grid(row=3,column=0,sticky=tk.W,pady=4)

        self.RadioY = tk.Radiobutton(self.prefdialog, text="Y:", variable=self.driveletter,
            value="Y:", command=lambda: print(self.driveletter.get()))
        self.RadioY.grid(row=3,column=1,sticky=tk.W,pady=4)

        self.state_checkbox = tk.Checkbutton(
            self.prefdialog, text="Check to use state folders",
            variable=self.statevalue, command=lambda: print(self.statevalue.get()))
        self.state_checkbox.grid(row=4,column=0,sticky=tk.W,pady=4)

        self.prefdialog.mainloop()

问题根源 #

排查后确认问题出在两个关键错误：

• 弹窗错误使用tk.Tk()创建实例：Tkinter要求一个应用只能有一个Tk()主窗口，弹窗应使用Toplevel()创建，它会依附于已存在的主窗口
• 重复调用mainloop()：主窗口已经运行了一个mainloop()，弹窗再次调用会导致Tkinter的变量绑定机制混乱，控件无法正确更新变量值

修复后的代码 #

class preferences(Preferences):
    def save_preferences(self):
        # Used to reset the folder location desired by the user
        # 用Toplevel创建弹窗，依附于主窗口
        self.prefdialog = tk.Toplevel(self)
        self.prefdialog.title('Set Preferences')

        self.driveletter = tk.StringVar()
        self.driveletter.set("G:")
        self.statevalue = tk.IntVar()
        self.statevalue.set(1)
        self.fpath = '\Desktop'

        self.RadioG = tk.Radiobutton(self.prefdialog, text="G:", variable=self.driveletter,
            value="G:", command=lambda: print(self.driveletter.get()))
        self.RadioG.grid(row=3,column=0,sticky=tk.W,pady=4)

        self.RadioY = tk.Radiobutton(self.prefdialog, text="Y:", variable=self.driveletter,
            value="Y:", command=lambda: print(self.driveletter.get()))
        self.RadioY.grid(row=3,column=1,sticky=tk.W,pady=4)

        self.state_checkbox = tk.Checkbutton(
            self.prefdialog, text="Check to use state folders",
            variable=self.statevalue, command=lambda: print(self.statevalue.get()))
        self.state_checkbox.grid(row=4,column=0,sticky=tk.W,pady=4)
        
        # 移除弹窗的mainloop()，依赖主窗口的mainloop()即可
        # self.prefdialog.mainloop()

内容的提问来源于stack exchange，提问作者Ryan