Life Cycle Components

Life Cycle Aware Components

• Most of the code is written inside Activity LifeCycle Methods - onCreate, onResume, onPause etc.

• Due to this, Activity has multiple responsibilities. But there are scenarios where we want to take actions based on the activity lifeCycle. For e.g.
• Access the User's Location.
• Playing Video.
• Downloading Images.

Life Cycle Aware Components Type

1. Owner ( Who has its Own Life cycle )
• Activity
• Fragment

2. Life Cycle Observer

Need :

• Observer will keep watch on Owner’s Lifecycle state

• and it will perform some task based on its state

• Its Helps to separate code for lifecycle methods from Owner (Activity)

• It helps to make clean architecture

Example:

Observer.kt

package com.example.androidarchitecture

import android.util.Log
import androidx.lifecycle.Lifecycle
import androidx.lifecycle.LifecycleObserver
import androidx.lifecycle.OnLifecycleEvent

class Observer : LifecycleObserver {

    @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
    fun onCreate() {
        Log.d("====", "Observer - onCreate")
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
    fun onResume() {
        Log.d("====", "Observer - onResume")
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_STOP)
    fun onStop() {
        Log.d("====", "Observer - onStop")
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
    fun onPause() {
        Log.d("====", "Observer - onPause")
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
    fun onDestroy() {
        Log.d("====", "Observer - onDestroy")
    }
}

MainActivity.kt

package com.example.androidarchitecture

import android.os.Bundle
import android.util.Log
import androidx.appcompat.app.AppCompatActivity
import com.example.androidarchitecture.databinding.ActivityMainBinding

class MainActivity : AppCompatActivity() {

    private val TAG: String = "===="

    private val binding: ActivityMainBinding by lazy {
        ActivityMainBinding.inflate(layoutInflater)
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(binding.root)
        
        // add LifeCycle Observer on Our Activity
        lifecycle.addObserver(Observer())

        Log.d("====", "Activity onCreate")
        
    }

    override fun onResume() {
        super.onResume()
        Log.d(TAG, "Activity - onResume")
    }

    override fun onPause() {
        super.onPause()
        Log.d(TAG, "Activity - onPause")
    }

    override fun onStop() {
        super.onStop()
        Log.d(TAG, "Activity - onStop")
    }

    override fun onDestroy() {
        super.onDestroy()
        Log.d(TAG, "Activity - onDestroy")
    }

}

Benefits:

• so Our life cycle observer is separate from activity so we can assign this observer to multiple Activities Or Fragments without copy & pasting same task on each components.

• when Activity lifecycle method called Observer automatically invoke method relate to that method Or has Connection with that method from observer class