TKInter按钮的全局变量

Question

我使用来自 Steven M. Vascellaro 示例Switch between two frames in tkinter的多帧窗口。 而且我不知道是否可以使用全局变量，因为每次更改时每个框架都会被破坏。如果我单击第二个按钮并转到StartPage并在那里执行某项操作并返回到StartPage，则必须激活PageOne上的第一个按钮（共2个按钮），必须激活第一个按钮。

如果我在global类中声明StartPage

_tkinter.TclError: invalid command name ".!startpage.!button2"

如果我在PageOne类中声明了它

NameError: name 'install_svc' is not defined

不是个好主意，但我想到了第三帧，我再次定义了按钮。

EDIT1：

class MyGUI(tk.Tk):
    def __init__(self):
        tk.Tk.__init__(self)

        self._frame = None
        self.switch_frame(StartPage)
        self.geometry("400x300")

    def switch_frame(self, frame_class):
        """Destroys current frame and replaces it with a new one."""
        new_frame = frame_class(self)
        if self._frame is not None:
            self._frame.destroy()
        self._frame = new_frame
        self._frame.pack()

    def quit_app(self):
        self._frame.destroy()
        self.destroy()

class StartPage(tk.Frame):
    def __init__(self, parent):
        tk.Frame.__init__(self, parent)
        global install_svc

class PageOne(tk.Frame):
    def __init__(self, parent):
        tk.Frame.__init__(self, parent)
    def entry_check(self,parent):
        global install_svc

Answer 1

在根级别（全局范围）声明并初始化install_svc。语句global install_svc本身不会自动神奇地创建全局范围内的变量：它只会查找具有该名称的全局变量，但是，如果您尝试使用该变量而没有先给它分配任何东西，它会抛出NameError。

代码

install_svc = None # Or some other initial value

class MyGUI(tk.Tk):
    def __init__(self):
        tk.Tk.__init__(self)

        self._frame = None
        self.switch_frame(StartPage)
        self.geometry("400x300")

    def switch_frame(self, frame_class):
        """Destroys current frame and replaces it with a new one."""
        new_frame = frame_class(self)
        if self._frame is not None:
            self._frame.destroy()
        self._frame = new_frame
        self._frame.pack()

    def quit_app(self):
        self._frame.destroy()
        self.destroy()

class StartPage(tk.Frame):
    def __init__(self, parent):
        tk.Frame.__init__(self, parent)
        global install_svc

        # You can use install_svc safely
        print(install_svc)

class PageOne(tk.Frame):
    def __init__(self, parent):
        tk.Frame.__init__(self, parent)
    def entry_check(self,parent):
        global install_svc

        # You can use install_svc safely
        print(install_svc)

您还可以执行try..except来检查变量是否存在，但这将非常难看（至少对我而言），并且您将需要在所有地方进行此类检查：< / p>

class MyGUI(tk.Tk):
    def __init__(self):
        tk.Tk.__init__(self)

        self._frame = None
        self.switch_frame(StartPage)
        self.geometry("400x300")

    def switch_frame(self, frame_class):
        """Destroys current frame and replaces it with a new one."""
        new_frame = frame_class(self)
        if self._frame is not None:
            self._frame.destroy()
        self._frame = new_frame
        self._frame.pack()

    def quit_app(self):
        self._frame.destroy()
        self.destroy()

class StartPage(tk.Frame):
    def __init__(self, parent):
        tk.Frame.__init__(self, parent)
        global install_svc

        try:
            install_svc
        except NameError:
            install_svc = None # Or some initial value

class PageOne(tk.Frame):
    def __init__(self, parent):
        tk.Frame.__init__(self, parent)
    def entry_check(self,parent):
        global install_svc

        try:
            install_svc
        except NameError:
            install_svc = None # Or some initial value