Pagination basics in Android Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What happens when you scroll to the bottom of this RecyclerView?

Given this Kotlin code snippet for a RecyclerView with pagination, what is the expected behavior when the user scrolls to the bottom?

Android Kotlin

recyclerView.addOnScrollListener(object : RecyclerView.OnScrollListener() {
  override fun onScrolled(rv: RecyclerView, dx: Int, dy: Int) {
    super.onScrolled(rv, dx, dy)
    val layoutManager = rv.layoutManager as LinearLayoutManager
    val totalItemCount = layoutManager.itemCount
    val lastVisible = layoutManager.findLastVisibleItemPosition()
    if (lastVisible == totalItemCount - 1) {
      loadNextPage()
    }
  }
})

A The app loads the next page of data by calling loadNextPage() when the last item is visible.

B The app refreshes the entire list from the first page when the bottom is reached.

C Nothing happens because onScrolled is not triggered at the bottom.

D The app crashes because findLastVisibleItemPosition() is not a valid method.

💡 Hint

Think about what happens when the last visible item matches the total items minus one.

The code listens for scroll events and checks if the last visible item is the last in the list. If yes, it triggers loading the next page.

🧠 Conceptual

intermediate

Why use pagination in mobile apps?

Which of these is the main reason to implement pagination in a mobile app?

A To make the UI more colorful and attractive.

B To reduce memory usage and improve performance by loading data in chunks.

C To load all data at once for faster access.

D To prevent users from scrolling too fast.

💡 Hint

Think about how loading large data sets affects app speed and memory.

Pagination helps by loading only a small part of data at a time, saving memory and making the app faster.

📝 Syntax

advanced

What is the output of this Kotlin code for a paginated list?

Consider this code snippet that appends new items to a list during pagination. What will be the size of 'items' after running?

Android Kotlin

val items = mutableListOf(1, 2, 3)
val newItems = listOf(4, 5)
items.addAll(newItems)
println(items.size)

A Compilation error

B 3

C 2

D 5

💡 Hint

What does addAll() do to the list?

addAll() adds all elements from newItems to items, increasing its size from 3 to 5.

❓ lifecycle

advanced

When should you reset pagination state in an Android app?

In an app with pagination, when is it best to reset the current page number and clear loaded data?

A When the user performs a new search or refreshes the list.

B Only when the app is closed and reopened.

C Never, keep loading pages continuously without reset.

D When the device orientation changes.

💡 Hint

Think about when the data source changes completely.

Resetting pagination on new search or refresh ensures the list shows fresh data from page one.

🔧 Debug

expert

Why does this pagination code cause duplicate items?

This Kotlin code appends new page data but sometimes shows duplicates. Why?

Android Kotlin

fun loadNextPage() {
  val newData = fetchData(page)
  items.addAll(newData)
  adapter.notifyDataSetChanged()
  page += 1
}

// fetchData returns the same data for page 1 and 2 by mistake

A adapter.notifyDataSetChanged() removes old items causing duplicates.

B items.addAll(newData) clears the list before adding, so duplicates appear.

C fetchData returns duplicate data for different pages, causing duplicates in 'items'.

D page variable is never incremented, so same page loads repeatedly.

💡 Hint

Check what fetchData returns for each page.

If fetchData returns the same data for multiple pages, adding it causes duplicates in the list.