Polling in android when only app is not minimized

Question

Lets say I have a method printCount() that print values every second, I want the polling to stop when the android app is minimized. For an example if it was minimized at count = 15 and if I open it after 5 mins, It should resume the polling and print the count from 16. Polling shouldn't run on background when app is minimized.

• What is the easiest and best way to achieve this in android?
• Also is there a RxJava approach to achieve this?

Answer 1

This can be achieved in many ways, using Handler, RxJava, Coroutines, etc.

1. Using RxJava:

   Observable.interval() method, which emits after a particular time interval specified.

   When the app is minimized, onStop() method is called and the observable stops emitting by calling disposable?.dispose(), and starts again in onStart(). I have used global variable for maintaining the count.

   class MainActivity : AppCompatActivity() {
   
    private lateinit var counterText: TextView
    private var counter: Int = 0
    private var disposable: Disposable? = null
   
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        counterText = findViewById(R.id.count)
    }
   
    override fun onStart() {
        super.onStart()
        disposable = Observable.interval(1000, TimeUnit.MILLISECONDS)
            .subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe { printCount() }
    }
   
    private fun printCount() {
        counter++
        counterText.text = counter.toString()
    }
   
    override fun onStop() {
        super.onStop()
        disposable?.dispose()
    }
   }
   

2. Using Kotlin coroutines:

   class MainActivity : AppCompatActivity() {
   
     private lateinit var counterText: TextView
     private var counter: Int = 0
     private var job: Job? = null
   
     override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        counterText = findViewById(R.id.count)
     }
   
     override fun onStart() {
        super.onStart()
        job = CoroutineScope(Job() + Dispatchers.Main).launch {
            while (true) {
               printCount()
               delay(1000)
            }
        }
     }
   
     private fun printCount() {
        counter++
        counterText.text = counter.toString()
     }
   
     override fun onStop() {
        super.onStop()
        job?.cancel()
     }
   }