Is there a `fun WindowInsets.asPaddingValues(): Pa...

# compose

[Stylianos Gakis]

Is there a fun WindowInsets.asPaddingValues(): PaddingValues alternative which does respect incoming already consumed paddings?
Modifier.windowInsetsPadding does work, but I need my value as PaddingValues so that I can pass it as contentPadding to a LazyColumn
Is the answer still that we must still do the onConsumedWindowInsetsChanged dance manually?

[Stylianos Gakis]

I am doing this rn

var consumedWindowInsets by remember { mutableStateOf(WindowInsets(0.dp)) }
LazyColumn(
 contentPadding = WindowInsets.safeDrawing
  .exclude(consumedWindowInsets)
  .asPaddingValues(),
 modifier = Modifier.onConsumedWindowInsetsChanged {
  consumedWindowInsets = it
 }
)

But I feel like there is room for an API here which reads the composition local for you and does this for you instead.

[Alex Vanyo]

Yeah, the manual dance is still necessary.

reads the composition local

Inset consumption is done at the ModifierLocal level, not via a composition local, so there isn’t a general way to pull out the consumed inset values from @Composable unless you’re at a particular spot in the hierarchy, which is what Modifier.onConsumedWindowInsetsChanged can do, since its a Modifier

[Stylianos Gakis]

I see, of course. The only way that surfaces is in modifiers that are extending from ModifierLocalConsumer but that is as you said, only for modifiers

[Stylianos Gakis]

I think I understood this last year as well, but it took me one year to forget about how all of this is hooked up together.
I might be back with the same question in 2025, no promises

[Alex Vanyo]

Exactly. Also there’s a slightly better way to use onConsumedWindowInsetsChanged in this case:

val safeDrawingInsets = WindowInsets.safeDrawing
val insetsForContentPadding = remember { MutableWindowInsets() }

LazyColumn(
 contentPadding = insetsForContentPadding.asPaddingValues(),
 modifier = Modifier.onConsumedWindowInsetsChanged {
  insetsForContentPadding.insets = safeDrawingInsets.exclude(it)
 }
)

That should allow you to have the correct consumed inset values on the first frame

[Alex Vanyo]

And this should be equivalent too actually, which is closer to your original setup:

var consumedWindowInsets = remember { MutableWindowInsets() }
LazyColumn(
 contentPadding = WindowInsets.safeDrawing
  .exclude(consumedWindowInsets)
  .asPaddingValues(),
 modifier = Modifier.onConsumedWindowInsetsChanged {
  consumedWindowInsets.insets = it
 }
)

[Stylianos Gakis]

Mr. First frame at it again!

So is this because instead of initializing a mutable state, then reading it initially, then setting it from inside the lambda we need to wait for one recomposition to happen before we get the final value?
But with this we are now creating the MutableWindowInsets object but we're mutating it internally the moment we hit that lambda? And due to the ordering of things, the internal value of it is read after that lambda was hit?

[Alex Vanyo]

Precisely

[Alex Vanyo]

And its important that the internals of both WindowInsets and PaddingValues are all “lazy”, they don’t calculate the values upon construction, they defer the reads until they are needed

[Stylianos Gakis]

Looks like yet another trick up my compose sleeve.
What can I say, thanks so much Alex, once again!

[Alex Vanyo]

You’re welcome!

[Alex Vanyo]

At the risk of creating nightmares about pointers:

State holders and nested state holders creates a giant system of pointers that’s entirely observable and reactive by design

[Alex Vanyo]

This resolves the first frame issue by creating an additional layer of pointers: Instead of manipulating the directly calculated values for the spacing in composition, we only manipulate pointers (that are internally capable of directly calculating values) in composition

[Alex Vanyo]

If you print out the result of asPaddingValues().toString() , you should see the whole chain of operations used to create the final “pointer” PaddingValues that’s used to drive the content padding

[Stylianos Gakis]

Btw very good tip about doing the toString() on the PaddingValues, it prints out the chain as you said, it gave me a good picture of what I was dealing with here!