Launch coroutine from click event in fragment

Issue

What is the proper way to launch a coroutine from a click event that is defined in a fragment? From my understanding, GlobalScope.launch is used if you want to launch a coroutine that is supposed to remain in memory for the entire lifecycle of the app. But since a fragment usually has a shorter lifecycle than the app, GlobalScope.launch probably isn't the proper way. I assume that if I used GlobalScope.launch, it might keep the fragment from being garbage collected?

I really only need to launch the coroutine from a click event handler, which means that there is no parent functions that I would be calling from.

Solution

You need a job to handle the coroutine cancelation to prevent leaks:

//inside Fragment
val job = Job()
val uiScope = CoroutineScope(Dispatchers.Main + job)


//late in the button click

button.setOnClickListener{
  uiScope.launch(Dispatchers.IO){
    //asyncOperation
    withContext(Dispatchers.Main){
     //ui operation
   }

  }
}

//later in on destroy:

override fun onDestroy(){
  job.cancel()
  super.onDestroy()
}

You can also use LifecycleScope extension from Google:

class MyFragment: Fragment() {
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        lifecycleScope.launch {
            val params = TextViewCompat.getTextMetricsParams(textView)
            val precomputedText = withContext(Dispatchers.Default) {
                PrecomputedTextCompat.create(longTextContent, params)
            }
            TextViewCompat.setPrecomputedText(textView, precomputedText)
        }
    }
}

Edit, in case you would re-fire another operation. Just use the same scope:

//let's assume you have a second button

button2.setOnClickListener{
  uiScope.launch(Dispatchers.IO){
    //perform second operation
  }
}

Answered By - coroutineDispatcher