Activity lifecycle methods (onCreate, onStart, onResume, onPause, onStop, onDestroy) in Android Kotlin

Introduction

Activity lifecycle methods help your app know what to do when the screen opens, closes, or changes. They keep your app working smoothly and save resources.

When you want to set up your screen when it first opens.

When you need to pause a video or game when the user switches apps.

When you want to save data before the app closes.

When you want to restart animations or refresh data when the user returns.

When you want to clean up resources to save battery and memory.

Syntax

Android Kotlin

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    // Initialize your activity here
}

override fun onStart() {
    super.onStart()
    // Activity is becoming visible
}

override fun onResume() {
    super.onResume()
    // Activity starts interacting with the user
}

override fun onPause() {
    super.onPause()
    // Activity is partially visible, pause ongoing actions
}

override fun onStop() {
    super.onStop()
    // Activity is no longer visible
}

override fun onDestroy() {
    super.onDestroy()
    // Clean up resources before activity is destroyed
}

Each method calls super to keep the system working properly.

Methods run in a specific order as the activity moves through states.

Examples

Set the layout when the activity is created.

Android Kotlin

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

Pause ongoing actions when the activity is partially hidden.

Android Kotlin

override fun onPause() {
    super.onPause()
    // Pause music or animations here
}

Clean up before the activity is destroyed to avoid memory leaks.

Android Kotlin

override fun onDestroy() {
    super.onDestroy()
    // Release resources like database or sensors
}

Sample App

This example logs messages to the console each time a lifecycle method runs. You can watch these logs to understand when each method is called as you open, use, and close the app.

Android Kotlin

import android.os.Bundle
import android.util.Log
import androidx.appcompat.app.AppCompatActivity

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        Log.d("Lifecycle", "onCreate called")
    }

    override fun onStart() {
        super.onStart()
        Log.d("Lifecycle", "onStart called")
    }

    override fun onResume() {
        super.onResume()
        Log.d("Lifecycle", "onResume called")
    }

    override fun onPause() {
        super.onPause()
        Log.d("Lifecycle", "onPause called")
    }

    override fun onStop() {
        super.onStop()
        Log.d("Lifecycle", "onStop called")
    }

    override fun onDestroy() {
        super.onDestroy()
        Log.d("Lifecycle", "onDestroy called")
    }
}

Important Notes

Use onCreate to set up your UI and initialize variables.

onPause and onStop are good places to save data or pause tasks.

onDestroy is the last chance to clean up before the activity is removed.

Summary

Activity lifecycle methods let your app respond to changes in screen visibility and user interaction.

Always call super in each lifecycle method to keep the system stable.

Use these methods to manage resources, save data, and keep your app smooth and efficient.