Saving instance state in Android Kotlin

Introduction

Saving instance state helps keep your app's data safe when the screen rotates or the app is temporarily stopped. It prevents losing what the user was doing.

When the user rotates the phone and you want to keep the current screen data.

When the app goes to the background and might be killed by the system.

When you want to save temporary user input like text typed in a form.

When you want to restore UI state like scroll position after a configuration change.

Syntax

Android Kotlin

override fun onSaveInstanceState(outState: Bundle) {
  super.onSaveInstanceState(outState)
  outState.putString("key", "value")
}

override fun onRestoreInstanceState(savedInstanceState: Bundle) {
  super.onRestoreInstanceState(savedInstanceState)
  val value = savedInstanceState.getString("key")
}

Use onSaveInstanceState to save data before the activity is destroyed.

Use onRestoreInstanceState or savedInstanceState in onCreate to restore data.

Examples

Saves an integer value with the key "score".

Android Kotlin

override fun onSaveInstanceState(outState: Bundle) {
  super.onSaveInstanceState(outState)
  outState.putInt("score", 42)
}

Restores the integer value saved with the key "score".

Android Kotlin

override fun onRestoreInstanceState(savedInstanceState: Bundle) {
  super.onRestoreInstanceState(savedInstanceState)
  val score = savedInstanceState.getInt("score")
}

Saves a boolean value to remember if a checkbox was checked.

Android Kotlin

override fun onSaveInstanceState(outState: Bundle) {
  super.onSaveInstanceState(outState)
  outState.putBoolean("isChecked", true)
}

Sample App

This app has a button that increases a number shown on screen. When you rotate the phone, the number stays the same because it is saved and restored using instance state.

Android Kotlin

import android.os.Bundle
import android.widget.Button
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity

class MainActivity : AppCompatActivity() {
  private var counter = 0
  private lateinit var counterText: TextView

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

    counterText = findViewById(R.id.counterText)
    val button = findViewById<Button>(R.id.incrementButton)

    if (savedInstanceState != null) {
      counter = savedInstanceState.getInt("counter")
    }
    counterText.text = counter.toString()

    button.setOnClickListener {
      counter++
      counterText.text = counter.toString()
    }
  }

  override fun onSaveInstanceState(outState: Bundle) {
    super.onSaveInstanceState(outState)
    outState.putInt("counter", counter)
  }
}

Important Notes

Always call super.onSaveInstanceState(outState) to let the system save default state.

Instance state is for small amounts of data like UI state, not for large files or databases.

Data saved in instance state is lost if the app is fully closed or the device restarts.

Summary

Saving instance state keeps UI data safe during screen rotations or temporary stops.

Use onSaveInstanceState to save data and onRestoreInstanceState or savedInstanceState in onCreate to restore it.

Good for saving small, temporary data like counters, text input, or checkbox states.