Seems like a noob question but can someone tell me...

# compose

[Afzal Najam]

Seems like a noob question but can someone tell me why it would be bad to pass an activity to a screen/top-level Composable (one that already takes a ViewModel for instance, so it’s not skippable)?

[Stylianos Gakis]

Why do your composables need to know about your activity? What are you trying to do?

[Afzal Najam]

For calculateWindowSizeClass but actually I’m just asking for knowledge. I know, for that, you can just calculate it and pass that down but I wanna know for doing a code review, what exactly is the reason.

[Stylianos Gakis]

Yes exactly, at the place you’d send an activity, simply calculate the WindowSizeClass there and send that instead.
Personally I’d request this to be changed if I saw an Activity being passed into a composable. I can’t think of a reason why I’d ever do it atm. No reason for a composable to know about Android like that imo.

[Afzal Najam]

Personally I’d request this to be changed if I saw an Activity being passed into a composable

Right, and I agree, but with what reason?

[Stylianos Gakis]

You said it yourself I guess, it makes the function not skippable for one. But on top of that it makes it less reusable too. If you pass the WindowSizeClass instead there’s a much bigger chance you’re gonna have that available to you to call this composable from various other places.

[Filip Wiesner]

I think the comments in documentation are pretty clear on the reason:

setContent {
    // Calculate the window size class for the activity's current window. If the window
    // size changes, for example when the device is rotated, the value returned by
    // calculateSizeClass will also change.
    val windowSizeClass = calculateWindowSizeClass(this)
    // Perform logic on the window size class to decide whether to use a nav rail.
    val useNavRail = windowSizeClass.widthSizeClass > WindowWidthSizeClass.Compact

    // MyScreen knows nothing about window size classes, and performs logic based on a
    // Boolean flag.
    MyScreen(useNavRail = useNavRail)
}

Especially the last comment:

MyScreen knows nothing about window size classes, and performs logic based on a Boolean flag.

Your Composable does not have to have any dependency on Activity or any other class. You can just tell it how it should behave and not on what data it should behave. The resulting Composable will be more reusable and more maintainable.

[Afzal Najam]

I guess de-coupling is enough of a reason. Thanks!