Hi, im migrating from rx java. Is there a way to make this flow synchrounous on main thread in android?

class MainActivity : AppCompatActivity() {

    private val scope = MainScope()

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

		Log.d("Default", "a")
        scope.launch {
            Log.d("Default", "b")
            flowOf(1)
                .collect { Log.d("Default", "coll=$it t=${Thread.currentThread().name}") }
        }
        Log.d("Default", "c")
    }
}

prints:
2020-10-18 04:14:26.808 21786-21786/sk.foo.flowplayground D/Default: a
2020-10-18 04:14:26.808 21786-21786/sk.foo.flowplayground D/Default: c
2020-10-18 04:14:26.848 21786-21786/sk.foo.flowplayground D/Default: b
2020-10-18 04:14:26.851 21786-21786/sk.foo.flowplayground D/Default: coll=1 t=main

I want:
2020-10-18 04:14:26.808 21786-21786/sk.foo.flowplayground D/Default: a
2020-10-18 04:14:26.808 21786-21786/sk.foo.flowplayground D/Default: b
2020-10-18 04:14:26.848 21786-21786/sk.foo.flowplayground D/Default: coll=1 t=main
2020-10-18 04:14:26.851 21786-21786/sk.foo.flowplayground D/Default: c

What is

MainScope()

? I think if you use

lifecycleScope

you'll get the behavior you want since it uses

Dispatchers.Main.immediate

by default

its from the standard library

package kotlinx.coroutines

public fun MainScope(): CoroutineScope = ContextScope(SupervisorJob() + Dispatchers.Main)

ill try the immediate thanks

lifecycleScope

also automatically handles cancellation when the activity is destroyed, so you always consider using that over creating your own scope. See the docs for more details: https://developer.android.com/topic/libraries/architecture/coroutines#lifecyclescope

I'm aware, im however not using fragments/so my viewmodels are custom class and I need to manually handle the main thread scope

Ah, your example code was in an activity, that was what was throwing me off

Yea just to show a minimal example, sorry. Also having that function in the core library feels kind of weird, what if I want the immediate as default, now I have to find some other good name or mess with imports and shoot my self in the foot

In general it's better to inject your dispatchers instead of hard-coding them, and then you can just change the dispatcher that gets injected. This is a good practice for Rx too for that matter.

sure .. its just a minimal repro; and commenting on necessity of such function in the library

yea agree there – i think there are a few too many “conveniences” in the lib.

GlobalScope

is another one.

also when its kinda harmful, doesnt expose the immediate as parameter etc, and now its public so its there forever