Android Studio - Korlin Coroutines --> Unresolved references: async & launch - android-studio

Question

I'm learning on Kotlin, and I'm in Coroutines.
I searched around the web, maybe the method i'm using is old? but i have async and launch(UI) aren't resolved...
my build.gradle:
plugins {
id 'com.android.application'
id 'kotlin-android'
id 'kotlin-android-extensions'
}
kotlin {
experimental {
coroutines 'enable'
}
}
...
dependencies {
implementation 'androidx.core:core-ktx:1.3.2'
implementation 'androidx.appcompat:appcompat:1.2.0'
implementation 'com.google.android.material:material:1.3.0'
implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
implementation 'org.jetbrains.kotlin:kotlin-serialization'
implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.3.8'
implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.4.1'
implementation 'org.jetbrains.anko:anko-commons:0.10.1'
testImplementation 'junit:junit:4.+'
androidTestImplementation 'androidx.test.ext:junit:1.1.2'
androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
}
the code to get data from api (UPDATED)
//getting data from api
fun fetchCharacterData(): Deferred<CharachterGenerator.CharacterData> {
CoroutineScope(Main).launch {
async { val apiData = URL(CHARACTER_DATA_API).readText()
CharachterGenerator.fromApiData(apiData)
}
}
return <--- how to get this correct, what should I return?
}
I use launch in a button setOnClickListener
generateButton.setOnClickListener {
CoroutineScope(Main).launch {
characterData = fetchCharacterData().await()
displayCharacterData()
}
}
displayCharacterData()
}
please bare with me I'm still learning...

Answer 1

launch and async are member functions of CoroutineScope. You can’t make bare calls to them unless you’re calling them from within a class that implements CoroutineScope. You may have seen this in the Kotlin documentation, but most of their examples are used within a runBlocking lambda, which provides a scope as function receiver. On Android, you typically will use the CorotuineScopes provided to you, like lifecycleScope or viewModelScope.
Edit after your update:
A common pattern for a function that does something asynchronously and returns a result is not to return a Deferred, but to make it a suspend function that directly returns a result using withContext:
suspend fun fetchCharacterData() = withContext(Dispatchers.IO) {
val apiData = URL(CHARACTER_DATA_API).readText()
CharachterGenerator.fromApiData(apiData)
}
Then when you call it your code is very simple because you don’t have to worry about what dispatcher you are on:
generateButton.setOnClickListener {
lifecycleScope.launch {
characterData = fetchCharacterData()
displayCharacterData()
}
}
It is a mistake to use the CoroutineScope() constructor-like function to create a one-off scope that you aren’t storing in a property where you can manage its lifecycle. You should rarely need to create your own since Android provides lifecycleScope and viewModelScope for you and manages their life cycles on your behalf.

Answer 2

After moving around on several other documentations I managed to do it this way
calling the API using async:
fun fetchCharacterData(): Deferred<CharachterGenerator.CharacterData> {
return CoroutineScope(IO).async { val apiData = URL(CHARACTER_DATA_API).readText()
CharachterGenerator.fromApiData(apiData)
}
}
making the request and getting the result then send it to be displayed
generateButton.setOnClickListener {
CoroutineScope(Main).launch {
characterData = fetchCharacterData().await()
displayCharacterData()
}
}