Lifecycle in Android

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Overview

Lifecycle has two components
  1. Lifecycle owner
  2. Lifecycle observer

Steps to follow

  • Add the required dependency in build.gradle (Module) file
   def lifecycle_version = "2.4.0"
   implementation "androidx.lifecycle:lifecycle-livedata-ktx:$lifecycle_version"
  • Create a class and extend it with LifecycleObserver class (Note: this method is deprecated)
 class MainActivityObserver : LifecycleObserver {
    @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
    fun onCreateCallback() {
        Log.d("Main", "Observer - onCreate")
    }

    @OnLifecycleEvent(Lifecycle.Event.ON_START)
    fun onStartCallBack() {
        Log.d("Main", "Observer - onStop")
    }

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

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

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

    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
    fun onDestroyCallback() {
        Log.d("Main", "Observer - onDestroy")
    }
 }
  • Create an object of the class in an Activity and use it in lifecycle.addObserver(...)
 class MainActivity : AppCompatActivity() {
    private lateinit var observer: MainActivityObserver
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        observer = MainActivityObserver()
        lifecycle.addObserver(observer)
        Log.d("Main", "Main - onCreate")
        addDefaultLifeCycleObserver()
    }

    override fun onStart() {
        super.onStart()
        Log.d("Main", "Main - onStart")
    }

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

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

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

    override fun onRestart() {
        super.onRestart()
        Log.d("Main", "Main - onRestart")
    }

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

    private fun addDefaultLifeCycleObserver() {
        val defaultLifecycleObserver = object : DefaultLifecycleObserver {
            override fun onCreate(owner: LifecycleOwner) {
                super.onCreate(owner)
                Log.d("Main", "DefaultLifecycleObserver - onCreate")
            }
        }
        lifecycle.addObserver(defaultLifecycleObserver)
    }
 }

Do's and Dont's

  • LifecycleObserver is deprecated. You have to use DefaultLifecycleObserver in the following manner
    private fun addDefaultLifeCycleObserver() {
        val defaultLifecycleObserver = object : DefaultLifecycleObserver {
            override fun onCreate(owner: LifecycleOwner) {
                super.onCreate(owner)
                Log.d("Main", "DefaultLifecycleObserver - onCreate")
            }
        }
        lifecycle.addObserver(defaultLifecycleObserver)
      }
    }

Reference





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