使用Tkinter开发GUI时金字塔体积无法显示问题求助

在使用Tkinter开发GUI时，计算金字塔体积后无法在界面显示结果。添加调试打印后，发现打印self.volume输出为"PY_VAR0"，调用set()方法赋值计算结果后仍无任何显示。相关代码如下：

def pyramid_button(self):
    # create the pyramid window
    self.pyramid_button_window = tkinter.Tk()
    self.pyramid_button_window.geometry('300x300')
    self.pyramid_button_window.title('Pyramid Volume')

    # create frames for secondary windows
    self.length_frame = tkinter.Frame(self.pyramid_button_window)
    self.width_frame = tkinter.Frame(self.pyramid_button_window)
    self.height_frame = tkinter.Frame(self.pyramid_button_window)
    self.volume_frame = tkinter.Frame(self.pyramid_button_window)
    self.button_frame = tkinter.Frame(self.pyramid_button_window)

    # create and pack widgets for pyramid length
    self.length_label = tkinter.Label(self.length_frame, text='Enter the base length of the pyramid:')
    self.length_entry = tkinter.Entry(self.length_frame, width=10)
    self.length_label.pack(side='left')
    self.length_entry.pack(side='left')

    # create and pack widgets for pyramid width
    self.width_label = tkinter.Label(self.width_frame, text='Enter the base  width of the pyramid:')
    self.width_entry = tkinter.Entry(self.width_frame, width=10)
    self.width_label.pack(side='left')
    self.width_entry.pack(side='left')

    # create and pack widgets for pyramid height
    self.height_label = tkinter.Label(self.height_frame, text='Enter the base  width of the pyramid:')
    self.height_entry = tkinter.Entry(self.height_frame, width=10)
    self.height_label.pack(side='left')
    self.height_entry.pack(side='left')

    # create and pack widgets for calculated pyramid volume
    self.volume_label = tkinter.Label(self.volume_frame, text='Volume: ')
    self.volume = tkinter.StringVar()
    self.calculated_volume_label = tkinter.Label(self.volume_frame, textvariable=self.volume)
    self.volume_label.pack(side='left')
    self.calculated_volume_label.pack(side='left')

    # create and pack button widgets
    self.p_calc_button = tkinter.Button(self.button_frame, text='Volume', command=self.calc_p_volume)
    self.p_close_button = tkinter.Button(self.button_frame, text='Close',
                                         command=self.pyramid_button_window.destroy)
    self.p_calc_button.pack(side='left')
    self.p_close_button.pack(side='left')

    # Pack the frames
    self.length_frame.pack()
    self.width_frame.pack()
    self.height_frame.pack()
    self.volume_frame.pack()
    self.button_frame.pack()

def calc_p_volume(self):
    # get length, width, height and store them
    # in variables

    self.length = float(self.length_entry.get())
    self.width = float(self.width_entry.get())
    self.height = float(self.height_entry.get())
    print(self.height, self.width, self.length)

    # calculate the volume

    self.p_volume = ((self.length * self.width * self.height)/3)
    print(self.p_volume)

    # update the volume label with calculated self.p_volume
    self.volume.set(self.p_volume)
    print(self.volume)

问题原因 #

核心问题是多Tk实例的变量绑定冲突：

• Tkinter中每个StringVar默认绑定到程序启动时创建的根Tk实例，你在子窗口中新建了第二个Tk()实例，导致self.volume绑定的是根实例而非子窗口实例。
• 调用self.volume.set()时，更新的是根实例绑定的变量，子窗口的标签无法感知到这个变化，所以界面无显示。
• 打印self.volume显示"PY_VAR0"是正常现象，这是StringVar对象的默认内部标识，并非错误。

解决方案 #

方案1：用Toplevel替代Tk创建子窗口 #

Toplevel是依附于主窗口的子窗口，会自动共享根Tk实例的变量上下文，是创建子窗口的标准方式：

def pyramid_button(self):
    # 将Tk()替换为Toplevel()
    self.pyramid_button_window = tkinter.Toplevel()
    self.pyramid_button_window.geometry('300x300')
    self.pyramid_button_window.title('Pyramid Volume')
    # 后续代码保持不变

方案2：为StringVar指定正确的master #

如果必须使用独立的Tk实例，创建StringVar时明确指定其所属的窗口实例：

# 在创建volume变量时指定master为子窗口
self.volume = tkinter.StringVar(master=self.pyramid_button_window)

额外提示 #

代码中存在一个小错误：高度输入框的标签文本写错了，当前是Enter the base width of the pyramid:，应该改为Enter the height of the pyramid:，避免用户输入混淆。

内容的提问来源于stack exchange，提问作者SheriffWoody95