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() } 

and the suspended function is:-

suspend fun callGetApi() {....} 

But the error shows up Suspend function 'callGetApi' should be called only from a coroutine or another suspend function

Answer 1

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' 

The BETTER APPROACH would be to use extension properties in ViewModel and Activity/Fragment:

• In ViewModel we can use viewModelScope to launch a coroutine:

  viewModelScope.launch { ... } 

It attached to the lifecycle of Activity/Fragment and cancels launched coroutines when they destroyed.

• Similar in Activity/Fragment we can use the following extension properties to launch a coroutine: lifecycleScope.launch {}, lifecycle.coroutineScope.launch {}, viewLifecycleOwner.lifecycleScope.launch {}(applicable in Fragments).

Answer 2

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"