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?

"What is the easiest and best way to achieve this in android?" -- what *exactly* is "this"? If "this" is "how do I determine when the app is 'minimized'?", use `ProcessLifecycleOwner`. — CommonsWare, Aug 06 '21 at 11:53

score 1 · Accepted Answer · answered Aug 08 '21 at 18:14

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

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()
 }
}

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()
  }
}

Thank you very much. This is exactly what I've wanted. Also do you know the difference using your approach for pausing/resuming and using ProcessLifecycleOwner? With ProcessLifecycleOwner I get 700 ms delay. Can I solve that with your approach? Would be great if there is something that fires before minimizing and before resuming — Sandeepa, Aug 09 '21 at 05:54

Polling in android when only app is not minimized

1 Answers1