How do you pass data between Fragments with Jetpack Navigation?

What's really being asked

This question tests your familiarity with the modern, recommended patterns for Android UI development. It specifically probes whether you know how to use the Jetpack Navigation component's type-safe argument passing mechanism (Safe Args) versus older, more error-prone methods like manually creating Bundles. It's a check for up-to-date, best-practice knowledge.

The full answer

A strong answer walks through four distinct steps. First, define the argument in the navigation graph XML file within the destination fragment's tag, specifying its name and app:argType (e.g., string, integer). Second, enable and apply the Safe Args Gradle plugin in your build.gradle files, which auto-generates type-safe classes. Third, in the source fragment, use the generated NavDirections class to create an action and pass the data as a typed parameter, then navigate using that action object. For example, SourceFragmentDirections.actionToDestination(userId = "abc-123"). Fourth, in the destination fragment, retrieve the arguments using the generated Args class, typically with the by navArgs() Kotlin property delegate.

The mistakes people make

A major red flag is suggesting manual Bundle creation (e.g., val bundle = Bundle().apply { putString("USER_ID", "123") } and passing it to navigate()). This is not type-safe and is the pre-Safe Args way of doing things. It indicates a lack of familiarity with modern tooling. Another less-than-ideal answer is immediately jumping to a shared ViewModel scoped to the Activity. While a valid pattern for sharing complex state, it's overkill for passing a simple, immutable ID from one screen to the next and isn't the direct answer to the question. Using Fragment constructors to pass data is a fundamental anti-pattern and a serious red flag.

What usually comes next

Expect questions like, "When would you choose a shared ViewModel over navigation arguments?" (Answer: For complex, mutable data or state that needs to survive beyond a single navigation event). Or, "How do you pass a custom Parcelable object?" (Answer: You specify the fully qualified class name in the app:argType attribute). A follow-up on the benefits of Safe Args is also common (Answer: Compile-time safety, null safety, and avoiding key/type mismatch errors at runtime).

A concrete example

In nav_graph.xml, the destination has <argument android:name="userId" app:argType="string" />. The source fragment calls val action = FirstFragmentDirections.actionFirstToSecond(userId = "user-99"); findNavController().navigate(action). The destination fragment retrieves it with private val args: SecondFragmentArgs by navArgs() and then accesses the value with args.userId.