What are the main difficulties and disadvantages you can name when implementing MVVM architecture?

Main challenges and drawbacks when implementing MVVM architecture on iOS:

• Support and debugging complexity: Due to the separation into Model, View, and ViewModel, it can sometimes be difficult to trace the data flow and understand where exactly an error occurred.
• Code redundancy: For simple screens, MVVM can lead to an excessive number of classes and files, complicating the project.
• Data binding: iOS does not have a built-in mechanism for two-way data binding like some other platforms, so third-party libraries or a lot of boilerplate code are often required.
• Memory leaks: Improper use of closures and references between View and ViewModel can lead to memory leaks.

Example of a memory leak issue:

class ViewModel {
    var onUpdate: (() -> Void)?
}

class ViewController: UIViewController {
    var viewModel = ViewModel()

    override func viewDidLoad() {
        super.viewDidLoad()
        viewModel.onUpdate = {
            self.updateUI() // Capturing self without [weak self] leads to a retain cycle
        }
    }

    func updateUI() {
        // UI update code
    }
}

To avoid this, weak references should be used in closures.