LastContentFocus.kt

40 lines · 1.7 KB

Changed in: 0.5.0

1	package dev.stave.ui.nav
2
3	import androidx.compose.runtime.MutableState
4	import androidx.compose.runtime.compositionLocalOf
5	import androidx.compose.runtime.mutableStateOf
6	import androidx.compose.ui.Modifier
7	import androidx.compose.ui.focus.FocusRequester
8	import androidx.compose.ui.focus.focusRequester
9	import androidx.compose.ui.focus.onFocusChanged
10
11	/**
12	* Holds the [FocusRequester] of the most recently focused content row so
13	* the Now Playing bar's Up gesture can restore focus to it — the user
14	* returns to exactly where they were, not wherever Compose's spatial
15	* resolver happens to pick.
16	*
17	* Screens that render content above the bar (Browse's list, Queue's
18	* list, etc.) write their row FRs here via [Modifier.trackLastContentFocus]
19	* on focus gain. The bar's `onUpFromBar` reads the current value and
20	* calls `requestFocus()` on it; when the row has been disposed (scrolled
21	* out of a LazyColumn) the call fails and the caller should fall back to
22	* [androidx.compose.ui.focus.FocusManager.moveFocus].
23	*
24	* Default value is a no-op sink so code that reads the Local without a
25	* provider (unlikely, but harmless) doesn't null-pointer.
26	*/
27	val LocalLastContentFocus =
28	compositionLocalOf<MutableState<FocusRequester?>> { mutableStateOf(null) }
29
30	/**
31	* Register [requester] as the "last focused content" when the modified
32	* element gains focus. Pair with a real [Modifier.focusRequester] and a
33	* focusable modifier (e.g. staveFocusable + clickable).
34	*/
35	fun Modifier.trackLastContentFocus(
36	requester: FocusRequester,
37	sink: MutableState<FocusRequester?>,
38	): Modifier = this
39	.focusRequester(requester)
40	.onFocusChanged { if (it.isFocused) sink.value = requester }