How to implement sticky header with parallax effect in a RecyclerView in Kotlin Android

How to implement sticky header with parallax effect in a RecyclerView in Kotlin Android.

Here is a detailed step-by-step tutorial on how to implement a sticky header with parallax effect in a RecyclerView in Kotlin Android.

Step 1: Set up the project

1. Create a new Android project in Kotlin.
2. Add the RecyclerView dependency to your app-level build.gradle file:

implementation 'androidx.recyclerview:recyclerview:1.2.1'

Step 2: Create the layout files

1. Open the activity_main.xml layout file and add a RecyclerView:

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/recyclerView"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

2. Create a new layout file for the header item (header_item.xml) and design it according to your requirements. This will be the layout for the sticky header view.

3. Create a new layout file for the regular items (item.xml) and design it according to your requirements. This will be the layout for the normal items in the RecyclerView.

Step 3: Create the Adapter class

1. Create a new Kotlin class called MyAdapter and make it extend RecyclerView.Adapter<MyAdapter.ViewHolder>.
2. Implement the necessary methods: onCreateViewHolder, onBindViewHolder, and getItemCount.

class MyAdapter : RecyclerView.Adapter<MyAdapter.ViewHolder>() {

    // ViewHolder class
    inner class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        // Bind views and define any necessary variables
    }

    // Create ViewHolder
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        val view = LayoutInflater.from(parent.context).inflate(R.layout.item, parent, false)
        return ViewHolder(view)
    }

    // Bind data to ViewHolder
    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        // Bind data to views in ViewHolder
    }

    // Return the number of items in the RecyclerView
    override fun getItemCount(): Int {
        // Return the total number of items
    }
}

Step 4: Implement sticky header logic

1. In the MyAdapter class, add a new method called isHeader to determine if the item at a given position is a header or not.

private fun isHeader(position: Int): Boolean {
    // Implement logic to determine if the item is a header or not
}

2. Create a new class called HeaderItemDecoration and make it extend RecyclerView.ItemDecoration.

class HeaderItemDecoration : RecyclerView.ItemDecoration() {
    // Implement necessary methods
}

3. Override the getItemOffsets method to set the top margin for the regular items to make space for the header.

override fun getItemOffsets(
    outRect: Rect,
    view: View,
    parent: RecyclerView,
    state: RecyclerView.State
) {
    val position = parent.getChildAdapterPosition(view)
    if (isHeader(position)) {
        outRect.set(0, headerHeight, 0, 0) // Set top margin for header
    } else {
        outRect.set(0, 0, 0, 0) // Reset margins for regular items
    }
}

4. Override the onDraw method to draw the sticky header on top of the regular items.

override fun onDraw(
    canvas: Canvas,
    parent: RecyclerView,
    state: RecyclerView.State
) {
    super.onDraw(canvas, parent, state)
    
    val childCount = parent.childCount
    val left = parent.paddingLeft
    val right = parent.width - parent.paddingRight
    
    for (i in 0 until childCount) {
        val child = parent.getChildAt(i)
        val position = parent.getChildAdapterPosition(child)
        
        if (isHeader(position)) {
            val layoutParams = child.layoutParams as RecyclerView.LayoutParams
            val top = child.top - layoutParams.topMargin - headerHeight
            val bottom = child.top - layoutParams.topMargin
            // Draw sticky header on canvas
        }
    }
}

Step 5: Set up the RecyclerView

1. In the MainActivity class, initialize the RecyclerView and the adapter.

val recyclerView: RecyclerView = findViewById(R.id.recyclerView)
val adapter = MyAdapter()

2. Set the adapter on the RecyclerView and set the layout manager.

recyclerView.adapter = adapter
recyclerView.layoutManager = LinearLayoutManager(this)

3. Add the HeaderItemDecoration to the RecyclerView.

recyclerView.addItemDecoration(HeaderItemDecoration())

4. Run the app to see the sticky header with parallax effect in action.

Congratulations! You have successfully implemented a sticky header with parallax effect in a RecyclerView using Kotlin in Android.