Android RecyclerView Adapter — Complete Guide

In this tutorial, you'll learn about Android RecyclerView Adapter. We cover key concepts, practical examples, and best practices to help you understand and apply this topic effectively.

The Problem

You create a new <a href="/design-patterns/adapter/">Adapter</a> instance on every data change, call notifyDataSetChanged() for single-item updates, or mutate the list without notifying the Adapter.

Wrong Approach ❌

class MyAdapter : RecyclerView.Adapter<MyAdapter.ViewHolder>() {
    private var items = mutableListOf<String>()

    // Exposing mutable list directly
    fun setItems(newItems: List<String>) {
        items = newItems.toMutableList()
        notifyDataSetChanged() // Massive overkill for single item change
    }

    fun addItem(item: String) {
        items.add(item) // Mutating without notification
    }
}

Output: Flickering list, IndexOutOfBoundsException, stale views.

Right Approach ✅

class MyAdapter : RecyclerView.Adapter<MyAdapter.ViewHolder>() {
    private var items: List<String> = emptyList()

    fun submitList(newItems: List<String>) {
        val old = items
        items = newItems
        // Use DiffUtil instead of full refresh
        DiffUtil.calculateDiff(object : DiffUtil.Callback() {
            override fun getOldListSize() = old.size
            override fun getNewListSize() = newItems.size
            override fun areItemsTheSame(i: Int, j: Int) = old[i] == newItems[j]
            override fun areContentsTheSame(i: Int, j: Int) = old[i] == newItems[j]
        }).dispatchUpdatesTo(this)
    }

    fun addItem(item: String) {
        val newList = items + item
        submitList(newList)
    }
}

Output: Smooth, animated list updates with minimal view rebinds.

Prevention

• Always use submitList() with DiffUtil or AsyncListDiffer.
• Never mutate the backing list directly.
• Avoid calling notifyDataSetChanged() — use targeted notifications.
• Use ListAdapter (built-in with AsyncListDiffer) for modern code.

Common Mistakes with recyclerview Adapter

1. Non-exhaustive pattern matches that compile with warnings then crash at runtime
2. Misunderstanding that String is [Char] with poor performance for large text operations
3. Using foldl instead of foldl' causing stack overflow on large lists

These mistakes appear frequently in real-world Android code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

FAQ