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Discover how to effectively transition your iOS app architecture from `MVC` to `MVVM` using delegate methods to manage `IBActions`. Explore best practices and common pitfalls to avoid!
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Refactoring iOS Apps: Transitioning from MVC to MVVM Using Delegates for IBActions

When it comes to building iOS applications, developers often face challenges that involve structuring their code effectively. The transition from the Model-View-Controller (MVC) architecture to Model-View-ViewModel (MVVM) can be a daunting task for beginners. One common question arises: how can we appropriately manage actions and maintain clean code? In this guide, we will explore how to use delegate methods to handle IBActions as part of this transition, along with addressing some common errors encountered during implementation.

The Problem

Imagine you’re building an app using Swift and Storyboards. You've started setting up your project with the necessary UI components and their corresponding actions. However, you encounter an issue where an action tied to a button in your storyboard is failing due to an unrecognized selector error. This error might often occur in the context of transitioning your architecture from MVC to MVVM.

The Solution

The good news is that refactoring your code and handling IBActions can be manageable when approached correctly. Let’s break down the steps needed to resolve this issue and adopt best practices for the MVVM pattern.

Understanding the Code Structure

To provide clarity, let’s review the critical elements of your implementation.

File 1 - TestDelegateView

This is the custom UIView class where your button and delegate are defined:

[[See Video to Reveal this Text or Code Snippet]]

In this file, a protocol TestDelegateViewDelegate is established, which requires any conforming types to implement the primaryAction() method. The button triggers primaryActionPressed, which invokes the delegate.

File 2 - TestDelegateViewController

In your ViewController, where you conform to the delegate protocol:

[[See Video to Reveal this Text or Code Snippet]]

Resolving the Issue

When you attempt to run the code, you encounter an error like the one below:

[[See Video to Reveal this Text or Code Snippet]]

This error signifies that a function, likely tied to the button within your storyboard, does not match any existing method in your code.

Debugging Steps

Check IBAction Connections: Open your storyboard and inspect the button’s connections. Verify that the action is correctly connected to primaryActionPressed and not a method called buttonAction, as indicated by the error message.

Renaming Methods: If you’ve renamed the IBAction method, it's crucial to reset the storyboard connections. Storyboards maintain connections to old method names and fail to recognize new ones until updated.

Delegate Setup: Ensure that the delegate is properly assigned before the button is pressed. You may assign the delegate in your ViewController’s viewDidLoad() method or before the view appears.

Best Practices for MVVM

When working with MVVM, consider the following best practices:

Keep Your Views Clean: Avoid placing business logic in your views. Use the ViewModel to handle this logic.

Delegate Methods: Use delegate methods for handling user input and actions, as shown in the TestDelegateView. This adheres to the MVVM separation of concerns.

Test Your Connections: Always double-check your storyboard connections to ensure each action is linked to the correct method to avoid unrecognized selector errors.

Conclusion

Transitioning from MVC to MVVM in your iOS applications can enhance your code's readability and maintainability. By leveraging delegate methods to handle IBActions and following best practices, you can create a more robust application architecture. If you encounter issues like the unrecognized selector error,