Resolving nil ViewModel Issues When Switching from MVC to MVVM in Swift

Learn how to transition from MVC to MVVM in Swift applications effectively by ensuring proper data transfer between view controllers.
---

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: I tried to make Swift MVC to MVVM but I can't get the data when I switch to the detail page?

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Resolving nil ViewModel Issues When Switching from MVC to MVVM in Swift

Transitioning from the Model-View-Controller (MVC) architecture to the Model-View-ViewModel (MVVM) architecture can be a daunting task, especially for developers who are used to the way data is passed in MVC. One common issue that arises during this transition is the inability to transfer data correctly between view controllers, particularly when navigating to a detail view. Let’s dive into the problem and explore how to resolve it, ensuring a smooth and effective data flow in your Swift application.

The Problem

You might encounter a scenario where you are trying to set up a detail view using the MVVM pattern, but you find that the information you are attempting to pass results in a nil ViewModel. Specifically, this occurs when implementing the prepare(for:sender:) method to transition to your DetailViewController.

When you try to access properties of your detail view's ViewModel, you realize that it hasn't been initialized properly, leaving you unable to work with the required data. Here's the relevant part of the code where the issue lies:

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

The problem here is that detailVC.viewModel is nil when you try to set its properties.

The Solution

To fix this issue, you need to create an instance of DetailViewModel and assign it to detailVC.viewModel during the segue preparation. This ensures that all required data is available when the detail view is presented. Here’s how to adjust your code:

Step 1: Initialize DetailViewModel

Replace the existing lines inside the prepare(for:sender:) function with the following code:

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

Step 2: Update DetailViewModel

Make sure you're passing any required properties to the DetailViewModel. As shown above, you should initialize the ViewModel with the necessary data, including the pokemonId and an instance of your apiService.

Additional Notes

Ensure that the apiService being passed is properly instantiated and available in the scope of the prepare(for:sender:) method.

In your DetailViewController, after setting the viewModel, make sure to call configureView() to initiate the data fetch and update the UI with the property values.

Here’s how your DetailViewController might look after these adjustments:

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

Conclusion

By ensuring that you properly initialize the viewModel before trying to access its properties, you can successfully transition your application from MVC to MVVM without losing the ability to pass necessary data between view controllers. This mindful structuring leads to a cleaner separation of concerns and a more maintainable codebase. Happy coding!