View Binding

// ❌ findViewById – easy to use the wrong id or wrong type
val tvMessage = findViewById<TextView>(R.id.tvMessage)
val btnHello = findViewById<Button>(R.id.btnHelo)      // typo → crash only at runtime

// app/build.gradle.kts
android {
    // ...
    buildFeatures {
        viewBinding = true
    }
}
// then: File → Sync Project with Gradle Files

package com.example.helloapp

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import com.example.helloapp.databinding.ActivityMainBinding

class MainActivity : AppCompatActivity() {

    private lateinit var binding: ActivityMainBinding
    private var count = 0

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)   // 1. inflate
        setContentView(binding.root)                           // 2. show its root view

        binding.btnHello.setOnClickListener {                  // 3. use ids as properties
            count++
            binding.tvMessage.text = "Namaste! You clicked $count times"
        }
    }
}

class NotesFragment : Fragment() {

    private var _binding: FragmentNotesBinding? = null
    private val binding get() = _binding!!          // valid only between onCreateView and onDestroyView

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View {
        _binding = FragmentNotesBinding.inflate(inflater, container, false)
        return binding.root
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        binding.tvTitle.text = "My notes"
    }

    override fun onDestroyView() {
        super.onDestroyView()
        _binding = null                               // avoid memory leaks
    }
}

class NoteAdapter(private val items: List<String>) :
    RecyclerView.Adapter<NoteAdapter.VH>() {

    class VH(val binding: ItemNoteBinding) : RecyclerView.ViewHolder(binding.root)

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int) =
        VH(ItemNoteBinding.inflate(LayoutInflater.from(parent.context), parent, false))

    override fun onBindViewHolder(holder: VH, position: Int) {
        holder.binding.tvTitle.text = items[position]
    }

    override fun getItemCount() = items.size
}

<!-- activity_main.xml -->
<include
    android:id="@+id/header"
    layout="@layout/layout_header" />

// Kotlin – the include becomes a nested binding
binding.header.tvHeaderTitle.text = "Dashboard"

<!-- to skip generating a binding class for a layout -->
<LinearLayout xmlns:tools="http://schemas.android.com/tools"
    tools:viewBindingIgnore="true" />