Python Tkinter类式多页面间变量传递后标签显示PY_VAR0的问题求助

Let's break down what's going wrong here and fix it step by step!

Key Problems in Your Code #

• You're replacing the StringVar object instead of updating its value: In your pageturn method, self.controller.shared_data["variable"] = 'string i wanna pass' overwrites the original tk.StringVar() instance with a plain string. That's why .get() throws errors later (strings don't have this method) and why you saw PY_VAR0 initially (that's the default string representation of an unmodified StringVar).
• Labels use static text instead of dynamic binding: Your page2 labels are created with fixed text at initialization. Even if you fixed the variable update, they wouldn't refresh unless you explicitly update them or use Tkinter's built-in variable binding.

Corrected Code with Explanations #

import tkinter as tk
from tkinter import ttk

class example(tk.Tk):
    def __init__(self, *args, **kwargs):
        tk.Tk.__init__(self, *args, **kwargs)
        # Keep the StringVar instance intact — we'll update its value later, not replace it
        self.shared_data = { "variable": tk.StringVar() }

        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 (page1, page2):
            frame = F(container, self)
            self.frames[F] = frame
            frame.grid(row=0, column=0, sticky="nsew")
        self.show_frame(page1)

    def get_page(self, page_class):
        return self.frames[page_class]

    def show_frame(self, cont):
        frame = self.frames[cont]
        # Trigger content update when switching to the frame (for static widgets)
        if hasattr(frame, "update_content"):
            frame.update_content()
        frame.tkraise()

class page1(tk.Frame):
    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        self.controller = controller

        label = ttk.Label(self, text="first page")
        label.grid(row=0, column=4, padx=10, pady=10)

        button1 = ttk.Button(self, text="turn page", command=lambda: self.pageturn())
        button1.grid(row=3, column=1, padx=10, pady=10)

    def pageturn(self):
        # Use .set() to update the StringVar's value — don't replace the object itself
        self.controller.shared_data["variable"].set('string i wanna pass')
        print("variable set here: ", self.controller.shared_data["variable"].get())
        self.controller.show_frame(page2)

class page2(tk.Frame):
    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        self.controller = controller
        self.var = self.controller.shared_data["variable"]

        # Use textvariable to bind the Label directly to the StringVar
        # This auto-updates the label whenever the variable changes
        self.dynamic_label = ttk.Label(self, textvariable=self.var)
        self.dynamic_label.grid(row=0, column=4, padx=10, pady=10)

        # For static labels that need manual updates, initialize with empty text
        self.static_label = ttk.Label(self, text="")
        self.static_label.grid(row=1, column=4, padx=10, pady=10)

        # Buttons can also use textvariable for dynamic text updates
        self.dynamic_button = ttk.Button(self, textvariable=self.var, command=lambda: print(self.var.get()))
        self.dynamic_button.grid(row=8, column=10, padx=10, pady=10)

        button2 = ttk.Button(self, text="Check variable value", command=lambda: self.ifok())
        button2.grid(row=9, column=10, padx=10, pady=10)

    def update_content(self):
        # Manually refresh static widgets when the page is shown
        self.static_label.config(text=self.var.get())

    def ifok(self):
        # Always use .get() to retrieve the actual string value from the StringVar
        if self.var.get() == 'string i wanna pass':
            print("Variable value is correct!")

app = example()
app.mainloop()

What We Fixed #

1. Proper StringVar updates:
   We use .set() to modify the value of the existing StringVar instead of replacing the object. This keeps the variable intact so .get() works as expected.

2. Dynamic widget binding:
   The textvariable parameter binds widgets directly to the StringVar. Any change to the variable automatically updates the widget's display, no manual refreshes needed.

3. Page switch content refresh:
   The show_frame method now calls an update_content method on the frame (if it exists) when switching pages. This ensures static widgets (like the second label) show the latest variable value when the page becomes visible.

4. Correct value retrieval:
   We consistently use .get() to fetch the actual string value from the StringVar, whether in print statements, condition checks, or manual widget updates.

This should resolve both the PY_VAR0 display issue and the variable passing/updating problems you were facing.

内容的提问来源于stack exchange，提问作者Andreasz