How to implement multi-select in a RecyclerView in Kotlin Android

How to implement multi-select in a RecyclerView in Kotlin Android.

Here's a step-by-step tutorial on how to implement multi-select in a RecyclerView in Kotlin for Android.

Step 1: Set up your project

Start by creating a new project in Android Studio and add the necessary dependencies in your app-level build.gradle file:

implementation 'androidx.recyclerview:recyclerview:1.2.1'

Step 2: Create the RecyclerView layout

Create a new XML layout file for the RecyclerView, which will be used to display the list items. For example, create a file called item_list.xml and add the following code:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical">

    <CheckBox
        android:id="@+id/item_checkbox"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Item"
        android:padding="8dp" />

</LinearLayout>

Step 3: Create the RecyclerView adapter

Create a new Kotlin file for the RecyclerView adapter, which will handle the data binding and view creation. For example, create a file called ListAdapter.kt and add the following code:

import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.CheckBox
import androidx.recyclerview.widget.RecyclerView

class ListAdapter(private val items: List<String>) :
    RecyclerView.Adapter<ListAdapter.ViewHolder>() {

    private val selectedItems = HashSet<Int>()

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

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        val item = items[position]
        holder.checkBox.text = item
        holder.checkBox.isChecked = selectedItems.contains(position)

        holder.checkBox.setOnClickListener {
            if (selectedItems.contains(position)) {
                selectedItems.remove(position)
            } else {
                selectedItems.add(position)
            }
            notifyDataSetChanged()
        }
    }

    override fun getItemCount(): Int {
        return items.size
    }

    inner class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        val checkBox: CheckBox = itemView.findViewById(R.id.item_checkbox)
    }

    fun getSelectedItems(): Set<Int> {
        return selectedItems
    }
}

Step 4: Set up the RecyclerView in your activity

In your activity layout XML file, add a RecyclerView element. For example, add the following code to your activity's XML layout file:

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

Then, in your activity's Kotlin file, initialize the RecyclerView and set up the adapter. Add the following code to your activity:

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView

class MainActivity : AppCompatActivity() {

    private lateinit var recyclerView: RecyclerView
    private lateinit var adapter: ListAdapter

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        recyclerView = findViewById(R.id.recycler_view)
        recyclerView.layoutManager = LinearLayoutManager(this)

        val items = listOf("Item 1", "Item 2", "Item 3", "Item 4", "Item 5")
        adapter = ListAdapter(items)
        recyclerView.adapter = adapter
    }
}

Step 5: Handle selected items

To retrieve the selected items from the RecyclerView, you can call the getSelectedItems() function from the adapter. For example, you can add a button in your activity layout and handle the click event to get the selected items:

val selectedItems = adapter.getSelectedItems()

That's it! You have now implemented multi-select in a RecyclerView in Kotlin for Android. You can customize the layout and functionality as per your requirements.