Item keys for performance in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to assign a unique key to each item in a LazyColumn for better performance.

Android Kotlin

LazyColumn {
  items(items = itemList, key = [1]) { item ->
    Text(text = item.name)
  }
}

Drag options to blanks, or click blank then click option'

Aitem.id

Bitem.name

CitemList.size

Ditem.hashCode()

Attempts:

3 left

💡 Hint

Common Mistakes

Using itemList.size as key causes all items to have the same key.

Using item.name might not be unique if names repeat.

Using a unique identifier like item.id as the key helps the LazyColumn track items efficiently and improves performance.

2fill in blank

medium

Complete the code to provide a stable key for each item in a RecyclerView adapter.

Android Kotlin

override fun getItemId(position: Int): Long {
  return [1]
}

Drag options to blanks, or click blank then click option'

ASystem.currentTimeMillis()

Bposition.toLong()

Citems.hashCode().toLong()

Ditems[position].id.toLong()

Attempts:

3 left

💡 Hint

Common Mistakes

Using position as ID can cause issues when items move.

Using current time causes keys to change every call.

Returning a unique stable ID like items[position].id.toLong() helps RecyclerView optimize item animations and updates.

3fill in blank

hard

Fix the error in the code to correctly set stable IDs in a RecyclerView adapter.

Android Kotlin

init {
  setHasStableIds([1])
}

Drag options to blanks, or click blank then click option'

Atrue

Bfalse

Cnull

Ditems.isNotEmpty()

Attempts:

3 left

💡 Hint

Common Mistakes

Passing false disables stable IDs, losing performance benefits.

Passing null causes a compile error.

Calling setHasStableIds(true) tells RecyclerView that each item has a unique stable ID, enabling better performance.

4fill in blank

hard

Fill both blanks to create a LazyRow with items that have unique keys.

Android Kotlin

LazyRow {
  items(items = [1], key = [2]) { item ->
    Text(text = item.title)
  }
}

Drag options to blanks, or click blank then click option'

AmyItemList

Bitem.id

Citem.title

Ditems

Attempts:

3 left

💡 Hint

Common Mistakes

Using items instead of the actual list variable.

Using item.title as key may not be unique.

Use the list variable myItemList and the unique item.id as the key for each item in LazyRow.

5fill in blank

hard

Fill all three blanks to create a RecyclerView adapter that uses stable IDs.

Android Kotlin

class MyAdapter(private val data: List<MyData>) : RecyclerView.Adapter<MyViewHolder>() {

  override fun getItemCount() = [1]

  override fun getItemId(position: Int): Long = [2]

  init {
    setHasStableIds([3])
  }

  // other adapter methods...
}

Drag options to blanks, or click blank then click option'

Adata.size

Bdata[position].uniqueId.toLong()

Ctrue

Dposition

Attempts:

3 left

💡 Hint

Common Mistakes

Returning position as ID instead of a unique stable ID.

Not enabling stable IDs with setHasStableIds(true).

Returning wrong item count.

The adapter returns the size of data, uses a unique stable ID for each item, and enables stable IDs with setHasStableIds(true).