Activity Lifecycle – Basics Of Android Kotlin

Basically, the one screen of mobile is knows as Activity in Android.

Android Activity Lifecycle is controlled by 7 methods which are included in android.app.Activity class. The android Activity is the subclass of ContextThemeWrapper class.

An activity is the single screen in android. It is like window or frame of Java.

By the help of activity, you can place all your GUI components or widgets in a single screen.

The activity goes from one state to another which is known as activity lifecycle.

Methods Of Activity Lifecycle

Method	Description
onCreate	called when activity is first created.
onStart	called when activity is becoming visible to the user.
onResume	called when activity will start interacting with the user.
onPause	called when activity is not visible to the user.
onStop	called when activity is no longer visible to the user.
onRestart	called after your activity is stopped, prior to start.
onDestroy	called before the activity is destroyed.

Life Cycle Diagram

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.tejsumeru.lifecycle">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
	    <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
	</activity>
        
    </application>
</manifest>

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

MainActivity.xml

Toast displays the pop up menu with short text message. The makeText() method is used with Toast, and at last show() method is used to show pop up.

package com.tejsumeru.lifecycle

import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.util.Log

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        Log.e("Activity","OnCreate")
    }

    override fun onStart() {
        super.onStart()
        Log.e("Activity","OnStart")
    }

    override fun onResume() {
        super.onResume()
        Log.e("Activity","OnResume")
    }

    override fun onPause() {
        super.onPause()
        Log.e("Activity","OnPause")
    }

    override fun onStop() {
        super.onStop()
        Log.e("Activity","OnStop")
    }

    override fun onDestroy() {
        super.onDestroy()
        Log.e("Activity","OnDestroy")
    }

    override fun onRestart() {
        super.onRestart()
        Log.e("Activity","OnRestart")
    }
}

OutPut

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