I have a behavior that I want a majority of my ViewModel classes to support. I considered creating a...

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[Colton Idle]

I have a behavior that I want a majority of my ViewModel classes to support. I considered creating a BaseViewModel, but I have also seen base classes that get out of control with if statements everywhere, and then it becomes clear that a base class wasn't the right approach.

I have seen the statement "favor composition over inheritence", but I haven't seen a practical example of it ever (or maybe I just never connected the dots). How would I make a class have this sort of behavior be composable (not to be confused with jetpack compose) instead of using inheritence? Do I just use interfaces since I can define multiple interfaces to implement? (I know that this is sort of not necessarily kotlin, but I figured it'd be worth a shot asking here)

[Dominaezzz]

I've also seen that statement but without the "favor" bit. Sometimes composition just works better since multiple inheritance is a PITA.
There are several ways to compose as you can imagine, since there's no keyword for it. Use case determines how you compose I guess.

[Dominaezzz]

Actually I take that back about the keyword. Delegation in Kotlin (by) is one way to achieve composition.

[Adam Powell]

start with something with a shape of

class MyViewModel : ViewModel() {
  val myBehavior = // ???

and then iterate from there. Represent the behavior as its own final class that accepts whatever dependencies it might need

[Adam Powell]

Polishing up the external interface once you have that can then start looking like what @Dominaezzz mentioned with class delegation or similar, or it might be as simple as manually declaring methods on the ViewModel that call methods on your behavior object

[Adam Powell]

You might end up with factory functions to help make setting things up a bit easier, maybe something like

fun ViewModel.createMyBehavior(...): MyBehavior = MyBehaviorImpl(...).also {
  viewModelScope.launch {
    it.runOngoingBehaviorStuff()
  }
}

[Colton Idle]

Thanks. Even just knowing that

val myBehavior = // ???

is a starting point is nice. I will iteratie on this today and this weekend to see if I can come up with something. Thank you all

[Daniel]

Âlso first check if you really need common behaviour for all your view models. From my experience lots of cases where the idea was thought necessarry could be avoided altogether