How to Get Variable Data from a Class

In the context of GUI programming, it is common to have multiple pages within a single application window. Each page may contain various widgets, such as entry fields, buttons, or labels. When interacting with these widgets, the user provides input or makes choices that need to be shared across different pages. This raises the question of how to access variable data from one class to another, especially when those classes represent different pages.

Leveraging Your Controller

One effective approach involves leveraging the concept of a controller class. In your provided code snippet, you have a MyApp class that manages multiple pages, such as PageOne and PageTwo. Typically, the controller acts as a mediator between different parts of the application and facilitates communication. Here's how you can use the controller to get variable data:

1. Add a reference to the controller in each page class:

   class PageOne(ttk.Frame):
       def __init__(self, parent, controller):
           self.controller = controller

2. Create a method in the controller to get a page instance by its class name:

   class MyApp(Tk):
       def get_page(self, classname):
           for page in self.frames.values():
               if str(page.__class__.__name__) == classname:
                   return page

3. Access the public members of the target page from another page:

   class PageTwo(ttk.Frame):
       def print_it(self):
           page_one = self.controller.get_page("PageOne")
           value = page_one.some_entry.get()

Storing Data in the Controller

Alternatively, you can consider storing shared data in the controller itself, rather than in the page classes. This approach decouples the pages from one another and reduces the need for tight coupling between them. Here's how it can be implemented:

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

   class MyApp(Tk):
       def __init__(self):
           self.app_data = {"name": StringVar(),
                            "address": StringVar()}

2. Modify each page to reference the controller's data structure when creating widgets:

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

3. Access the shared data from the controller instead of the page classes:

   class PageTwo(ttk.Frame):
       def print_it(self):
           value = self.controller.app_data["address"].get()

By implementing one of these approaches, you can effectively share variable data between different page classes within your GUI application. The controller-based approach provides tight coupling and a centralized point of control for communication, while storing data in the controller promotes decoupling and flexibility. The choice of approach depends on the specific requirements of your application and the level of interaction and data sharing needed between the pages.