MVVM pattern in iOS Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding MVVM Roles

In the MVVM pattern, which component is responsible for holding the UI logic and preparing data for display?

A Controller

B Model

C View

D ViewModel

💡 Hint

Think about which part acts as a bridge between data and UI.

The ViewModel holds UI logic and prepares data from the Model to be displayed by the View. It acts as a bridge between Model and View.

❓ ui_behavior

intermediate

View Updates in MVVM

In an MVVM iOS app using SwiftUI, when the ViewModel updates a @Published property, what happens to the View?

A The View automatically refreshes to reflect the new data.

B The View requires manual refresh calls to update.

C The Model triggers the View to update directly.

D The ViewModel must notify the ViewController to update the View.

💡 Hint

Consider how SwiftUI reacts to changes in @Published properties.

SwiftUI Views observe @Published properties in the ViewModel and automatically refresh when these properties change.

❓ lifecycle

advanced

ViewModel Lifecycle Management

Which of the following is the best practice to avoid memory leaks when a ViewModel holds a reference to a ViewController in MVVM on iOS?

A Use a strong reference to the ViewController in the ViewModel.

B Do not reference the ViewController at all in the ViewModel.

C Use a weak reference to the ViewController in the ViewModel.

D Use an unowned reference to the ViewController in the ViewModel.

💡 Hint

Think about how to prevent retain cycles between ViewModel and ViewController.

Using a weak reference prevents retain cycles and memory leaks when the ViewModel references the ViewController.

❓ navigation

advanced

Navigation Handling in MVVM

In MVVM, where should navigation logic (like pushing a new screen) ideally be handled to keep the ViewModel testable and free of UIKit dependencies?

A Inside the View, triggered by ViewModel signals.

B Directly inside the ViewModel using UIKit calls.

C Inside the Model layer.

D Inside the AppDelegate.

💡 Hint

Consider separation of concerns and testability.

Navigation should be handled by the View layer in response to signals or state changes from the ViewModel, keeping the ViewModel free of UIKit dependencies.

🔧 Debug

expert

Debugging MVVM Data Binding Issue

Given this SwiftUI ViewModel code snippet, why does the View not update when 'count' changes? class CounterViewModel: ObservableObject { var count = 0 func increment() { count += 1 } } What is the cause?

A The 'increment' method does not call objectWillChange.send(), so View is not notified.

B The 'count' property is not marked with @Published, so changes are not observed.

C The ViewModel does not conform to ObservableObject correctly.

D The View is not observing the ViewModel instance.

💡 Hint

Check how SwiftUI detects changes in ViewModel properties.

Without @Published, SwiftUI does not observe changes to 'count', so the View does not update.