How to create your own RecyclerView.Adapter for use in an Android application?

1. Create a class that inherits from RecyclerView.Adapter<ViewHolder>, where ViewHolder is an inner class inheriting from RecyclerView.ViewHolder.

2. Implement three abstract methods:

   • onCreateViewHolder(parent: ViewGroup, viewType: Int): Creates a new instance of ViewHolder. Usually, this involves inflating the layout of a list item.
   • onBindViewHolder(holder: ViewHolder, position: Int): Binds data to the views in the ViewHolder for the specified position.
   • getItemCount(): Int: Returns the total number of items in the data set.

3. Inside the adapter class, define a list or another container to store the data to be displayed.

4. In the onCreateViewHolder method, obtain a LayoutInflater from the parent context, then call inflater.inflate() to create the View for a list item. Pass the created View to the ViewHolder constructor.

5. Inside the inner ViewHolder class, get references to the View elements of the list item layout that need to be accessed. This is done in the ViewHolder constructor, which receives a View.

6. In the onBindViewHolder method, use position to get the corresponding data item from the collection. Then, set the properties of the View elements in the holder based on this data.

7. Add methods to update the data in the adapter (e.g., setData(newData: List<Item>) or addItem(item: Item)). After data changes, call methods to notify the RecyclerView of the changes, such as notifyDataSetChanged() or more specific ones like notifyItemInserted(), notifyItemRemoved(), notifyItemChanged(), notifyItemRangeChanged().

Example structure:

class MyAdapter(private var dataSet: List<String>) :
    RecyclerView.Adapter<MyAdapter.MyViewHolder>() {

    class MyViewHolder(view: View) : RecyclerView.ViewHolder(view) {
        val textView: TextView

        init {
            // Define click listener for the ViewHolder's View.
            textView = view.findViewById(R.id.textView) // Example ID from layout
        }
    }

    override fun onCreateViewHolder(viewGroup: ViewGroup, viewType: Int): MyViewHolder {
        val view = LayoutInflater.from(viewGroup.context)
            .inflate(R.layout.item_layout, viewGroup, false) // Example layout ID
        return MyViewHolder(view)
    }

    override fun onBindViewHolder(viewHolder: MyViewHolder, position: Int) {
        viewHolder.textView.text = dataSet[position]
    }

    override fun getItemCount() = dataSet.size

    fun updateData(newData: List<String>) {
        dataSet = newData
        notifyDataSetChanged() // Or more precise notify methods
    }
}

8. In the activity or fragment where the RecyclerView is used, create an instance of this adapter and set it to the RecyclerView using setAdapter(). Also, remember to set a LayoutManager for the RecyclerView (e.g., LinearLayoutManager).

// In Activity/Fragment
val recyclerView: RecyclerView = findViewById(R.id.recyclerView) // Example ID
val layoutManager = LinearLayoutManager(this) // Or another layout manager
recyclerView.layoutManager = layoutManager
val myAdapter = MyAdapter(initialData)
recyclerView.adapter = myAdapter

// Updating data
myAdapter.updateData(newData)