Suspend function 'callGetApi' should be called only from a coroutine or another suspend function

Question

I am calling suspended function from onCreate(...)

override fun onCreate(savedInstanceState: Bundle?) {
    ...
    ...
    callGetApi()
}

Answer 1

Looks like the most elegant way to do it as of July 2019, is the one described here:

import androidx.lifecycle.lifecycleScope
import kotlinx.coroutines.launch

class Activity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super...

        lifecycleScope.launch {
            val result =  callGetApi()
            onResult(result) 
        }
    }
}

Don't forget to add the correponding lib:

implementation "androidx.lifecycle:lifecycle-runtime-ktx:2.2.0-alpha02"

Answer 2

The above answer worked , but i solved it without inheriting CoroutineScope class by just using .... gradle.build

  dependencies {
      implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.3.3'
  }

Activity.kt

  import kotlinx.coroutines.GlobalScope
  import kotlinx.coroutines.Dispatchers

  GlobalScope.launch (Dispatchers.Main) { callGetApi() }

Dispatchers.Main is important cause you cannot update the UI in any other thread than main.

But its recommended to inherit CoroutineScope to maintain the lifecycle of the activity and onDestroy of the activity to kill the job

Answer 3

Suspend function should be called only from coroutine. That means you need to use a coroutine builder, e.g. launch. For example:

class Activity : AppCompatActivity(), CoroutineScope {
    private var job: Job = Job()

    override val coroutineContext: CoroutineContext
        get() = Dispatchers.Main + job

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

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        launch {
            val result =  callGetApi()
            onResult(result) // onResult is called on the main thread
        }
    }

    suspend fun callGetApi(): String {...}

    fun onResult(result: String) {...}
}

To use Dispatchers.Main in Android add dependency to the app's build.gradle file:

implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.0.1'