How to Pass Data Between Pages in a Tkinter Multi-Page Application?

How to Access Variable Data from a Class

Problem:

In a multi-page application using Tkinter, how can a class on one page access variable data stored in a class on a different page?

Leveraging Your Controller:

Assuming you're already utilizing a controller, you can exploit it for communication between pages.

1. Store a reference to the controller in each page:

   <code class="python">class PageOne(ttk.Frame):
    def __init__(self, parent, controller):
        self.controller = controller
        ...
   
   class PageTwo(ttk.Frame):
    def __init__(self, parent, controller):
        self.controller = controller
        ...</code>

2. Create a method in the controller to retrieve a page based on its class name:

   <code class="python">class MyApp(Tk):
    def get_page(self, classname):
        '''Returns an instance of a page given it's class name as a string'''
        for page in self.frames.values():
            if str(page.__class__.__name__) == classname:
                return page
        return None</code>

3. In the page that needs to access the data, use the get_page method:

   <code class="python">class PageTwo(ttk.Frame):
    def print_it(self):
        page_one = self.controller.get_page("PageOne")
        value = page_one.some_entry.get()
        print ('The value stored in StartPage some_entry = %s' % value)</code>

Storing Data in the Controller:

To reduce coupling between pages, consider storing the shared data in the controller.

1. Create a data structure in the controller to store the variables:

   <code class="python">class MyApp(Tk):
    def __init__(self):
        ...
        self.app_data = {"name":    StringVar(),
                         "address": StringVar(),
                         ...
                        }</code>

2. Update the pages to reference the controller's data:

   <code class="python">class PageOne(ttk.Frame):
    def __init__(self, parent, controller):
        self.controller=controller
        ...
        self.some_entry = ttk.Entry(self,
            textvariable=self.controller.app_data["name"], ...) </code>

3. Access the data from the controller:

   <code class="python"> def print_it(self):
        value = self.controller.app_data["address"].get()
        ...</code>

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