Sticky headers in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set a sticky header in a RecyclerView using a LayoutManager.

Android Kotlin

recyclerView.layoutManager = [1]

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AStaggeredGridLayoutManager(2, LinearLayoutManager.VERTICAL)

BLinearLayoutManager(this)

CGridLayoutManager(this, 2)

DFlexboxLayoutManager(this)

Attempts:

3 left

💡 Hint

Common Mistakes

Using GridLayoutManager when a simple vertical list is needed.

Forgetting to assign a LayoutManager to the RecyclerView.

LinearLayoutManager arranges items vertically or horizontally and is commonly used with sticky headers.

2fill in blank

medium

Complete the code to create a sticky header by attaching an ItemDecoration to the RecyclerView.

Android Kotlin

val stickyHeaderDecoration = [1](adapter)
recyclerView.addItemDecoration(stickyHeaderDecoration)

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ASnapHelper

BDividerItemDecoration

CItemTouchHelper

DStickyHeaderItemDecoration

Attempts:

3 left

💡 Hint

Common Mistakes

Using DividerItemDecoration which only draws dividers, not sticky headers.

Confusing ItemTouchHelper with decorations.

StickyHeaderItemDecoration is a custom or library class used to create sticky headers in RecyclerView.

3fill in blank

hard

Fix the error in the adapter method to provide header IDs for sticky headers.

Android Kotlin

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

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A-1L

B0L

Citems[position].headerId

Dposition.toLong()

Attempts:

3 left

💡 Hint

Common Mistakes

Returning position.toLong() which treats each item as a separate header.

Returning 0L which groups all items under one header.

Returning the headerId from the item at the given position groups items under the same header.

4fill in blank

hard

Fill both blanks to implement the onDrawOver method for drawing sticky headers.

Android Kotlin

override fun onDrawOver(c: Canvas, parent: RecyclerView, state: RecyclerView.State) {
    val topChild = parent.getChildAt(0) ?: return
    val topChildPosition = parent.getChildAdapterPosition(topChild)
    val header = [1](parent, topChildPosition)
    val contactPoint = header.bottom
    val childInContact = parent.[2](parent.width / 2f, contactPoint)
    // Draw header logic here
}

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AgetHeaderView

BfindChildViewUnder

CgetChildAt

DgetChildAdapterPosition

Attempts:

3 left

💡 Hint

Common Mistakes

Using getChildAt instead of findChildViewUnder for contact point detection.

Confusing getChildAdapterPosition with getHeaderView.

getHeaderView gets the header view for the position, and findChildViewUnder finds the child view at a specific y coordinate.

5fill in blank

hard

Fill all three blanks to complete the sticky header touch event handling.

Android Kotlin

override fun onInterceptTouchEvent(rv: RecyclerView, e: MotionEvent): Boolean {
    val headerView = rv.[1](e.x, e.y)
    if (headerView != null) {
        val position = rv.getChildAdapterPosition(headerView)
        [2](position)
        return true
    }
    return false
}

fun [3](position: Int) {
    // Handle header click
}

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AfindChildViewUnder

BonHeaderClick

CnotifyHeaderClick

DhandleHeaderClick

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong method names for click handling.

Not checking if headerView is null before proceeding.

findChildViewUnder locates the header view under touch, onHeaderClick is called on click, and handleHeaderClick defines the click behavior.

Practice

1. What is the main purpose of sticky headers in an Android RecyclerView?

easy

A. To keep section titles visible while scrolling

B. To add animations to list items

C. To load images asynchronously

D. To sort the list alphabetically

Solution

1. Step 1: Understand sticky header behavior

   Sticky headers keep section titles visible at the top as you scroll through grouped list items.

2. Step 2: Compare with other options

   Animations, image loading, and sorting are unrelated to sticky headers.

3. Final Answer:

   To keep section titles visible while scrolling -> Option A

4. Quick Check:

   Sticky headers = visible section titles [OK]

Hint: Sticky headers keep titles visible on scroll [OK]

Common Mistakes:

• Confusing sticky headers with animations
• Thinking sticky headers sort the list
• Assuming sticky headers load images

2. Which Android component is commonly used to implement sticky headers in Kotlin?

easy

A. RecyclerView with ItemDecoration

B. ListView with Adapter

C. ScrollView with LinearLayout

D. ViewPager with FragmentStateAdapter

Solution

1. Step 1: Identify components for sticky headers

   RecyclerView supports ItemDecoration which allows custom drawing for sticky headers.

2. Step 2: Eliminate other options

   ListView and ScrollView do not support sticky headers natively; ViewPager is for paging, not lists.

3. Final Answer:

   RecyclerView with ItemDecoration -> Option A

4. Quick Check:

   Sticky headers use RecyclerView + ItemDecoration [OK]

Hint: Sticky headers need RecyclerView + ItemDecoration [OK]

Common Mistakes:

• Choosing ListView instead of RecyclerView
• Using ScrollView which lacks sticky header support
• Confusing ViewPager with list components

3. Given this Kotlin code snippet for a RecyclerView ItemDecoration:

override fun onDrawOver(c: Canvas, parent: RecyclerView, state: RecyclerView.State) {
  val child = parent.getChildAt(0) ?: return
  val position = parent.getChildAdapterPosition(child)
  val header = getHeaderViewForItem(position)
  c.save()
  c.translate(0f, 0f)
  header.draw(c)
  c.restore()
}

What is the visible effect of this code when scrolling?

medium

A. The header blinks on every scroll event

B. The header stays fixed at the top while list scrolls underneath

C. The header appears at the bottom of the list

D. The header scrolls away with the list items

Solution

1. Step 1: Analyze onDrawOver behavior

   onDrawOver draws the header on top of the RecyclerView content, fixed at the top (0f, 0f).

2. Step 2: Understand scrolling effect

   Since header is drawn at fixed position, it stays visible while list scrolls underneath.

3. Final Answer:

   The header stays fixed at the top while list scrolls underneath -> Option B

4. Quick Check:

   onDrawOver + translate(0,0) = sticky header visible [OK]

Hint: onDrawOver draws sticky header at fixed top position [OK]

Common Mistakes:

• Thinking header scrolls away with items
• Assuming header appears at bottom
• Believing header blinks on scroll

4. You implemented sticky headers using ItemDecoration but headers flicker or disappear during fast scroll. What is the likely cause?

medium

A. Using LinearLayoutManager instead of GridLayoutManager

B. Setting RecyclerView height to wrap_content

C. Forgetting to call super.onDrawOver() in override

D. Not caching header views causing repeated layout calls

Solution

1. Step 1: Identify flicker cause in sticky headers

   Repeatedly creating and measuring header views without caching causes flicker during fast scroll.

2. Step 2: Check other options

   Layout manager type or calling super.onDrawOver() usually don't cause flicker; wrap_content affects layout size but not flicker.

3. Final Answer:

   Not caching header views causing repeated layout calls -> Option D

4. Quick Check:

   Missing header caching = flicker [OK]

Hint: Cache header views to avoid flicker [OK]

Common Mistakes:

• Ignoring header view caching
• Blaming layout manager type
• Forgetting super call but unrelated to flicker

5. You want to implement sticky headers that change smoothly when scrolling between sections in a RecyclerView. Which approach best achieves this effect?

hard

A. Use a separate fixed TextView outside RecyclerView for headers

B. Replace header view completely on every scroll event

C. Draw the current header at top and translate it up as next header approaches

D. Disable RecyclerView animations to prevent flicker

Solution

1. Step 1: Understand smooth sticky header transition

   Drawing current header at top and moving it up as next header scrolls in creates smooth push effect.

2. Step 2: Evaluate other options

   Replacing header fully causes flicker; separate TextView won't sync scrolling; disabling animations doesn't create smooth transition.

3. Final Answer:

   Draw the current header at top and translate it up as next header approaches -> Option C

4. Quick Check:

   Smooth sticky header = translate current header up [OK]

Hint: Translate header up for smooth sticky effect [OK]

Common Mistakes:

• Replacing header view causing flicker
• Using fixed TextView outside RecyclerView
• Disabling animations instead of translating header