How to Share Data Between Classes in a Multi-Page Application?

How to Access Variable Data Between Classes in a Multi-Page Application

In a multi-page application where each page is defined by a separate class, accessing variable data between classes can be challenging.

Leveraging the Controller

One approach is to use the application controller class to facilitate communication between pages. Add a reference to the controller to each page's constructor:

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

Next, add a method to the controller that retrieves a page instance given its class name:

<code class="python">class MyApp(Tk):
    ...
    def get_page(self, classname):
        for page in self.frames.values():
            if str(page.__class__.__name__) == classname:
                return page
        return None</code>

Then, from within one page, you can access another page's variable data:

<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 avoid tight coupling between pages, consider storing data in the controller rather than in specific pages:

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

Then, within each page, reference the controller's data structure when creating widgets:

<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>

Finally, access the data from the controller directly:

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

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