AsyncTask as kotlin coroutine

Question

Typical use for AsyncTask: I want to run a task in another thread and after that task is done, I want to perform some operation in my UI thread, namely hiding a progress bar

Answer 1

Another approach is to create generic extension function on CoroutineScope:

fun  CoroutineScope.executeAsyncTask(
        onPreExecute: () -> Unit,
        doInBackground: () -> R,
        onPostExecute: (R) -> Unit
) = launch {
    onPreExecute()
    val result = withContext(Dispatchers.IO) { // runs in background thread without blocking the Main Thread
        doInBackground()
    }
    onPostExecute(result)
}

Now we can use it with any CoroutineScope:

• In ViewModel:

    class MyViewModel : ViewModel() {
  
        fun someFun() {
            viewModelScope.executeAsyncTask(onPreExecute = {
                // ...
            }, doInBackground = {
                // ...
                "Result" // send data to "onPostExecute"
            }, onPostExecute = {
                // ... here "it" is a data returned from "doInBackground"
            })
        }
    }
  

• In Activity or Fragment:

    lifecycleScope.executeAsyncTask(onPreExecute = {
        // ...
    }, doInBackground = {
        // ...
        "Result" // send data to "onPostExecute"
    }, onPostExecute = {
        // ... here "it" is a data returned from "doInBackground"
    })
  

To use viewModelScope or lifecycleScope add next line(s) to dependencies of the app's build.gradle file:

implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$LIFECYCLE_VERSION" // for viewModelScope
implementation "androidx.lifecycle:lifecycle-runtime-ktx:$LIFECYCLE_VERSION" // for lifecycleScope

At the time of writing final LIFECYCLE_VERSION = "2.3.0-alpha05".