AutoScrollHorizontalPager を作る

• （擬似的に）無限ループしたい
• タップされているときは自動送りしない

view plainprint?

1. private const val PAGE_COUNT = 10_000  
2. private const val INITIAL_PAGE = PAGE_COUNT / 2  
3.   
4. private fun Int.floorMod(other: Int): Int = when (other) {  
5.     0 -> this  
6.     else -> this - this.floorDiv(other) * other  
7. }  
8.   
9. @Composable  
10. fun AutoScrollHorizontalPager(  
11.     itemSize: Int,  
12.     modifier: Modifier = Modifier,  
13.     autoScrollDuration: Long = 2_000L,  
14.     onPageChanged: ((page: Int) -> Unit)? = null,  
15.     pageContent: @Composable PagerScope.(page: Int) -> Unit,  
16. ) {  
17.     val pagerState = rememberPagerState(INITIAL_PAGE) { PAGE_COUNT }  
18.   
19.     fun Int.toIndex(): Int = (this - INITIAL_PAGE).floorMod(itemSize)  
20.   
21.     if (onPageChanged != null) {  
22.         LaunchedEffect(onPageChanged) {  
23.             snapshotFlow { pagerState.currentPage }  
24.                 .collect { page -> onPageChanged(page.toIndex()) }  
25.         }  
26.     }  
27.   
28.     val dragged by pagerState.interactionSource.collectIsDraggedAsState()  
29.     if (!dragged) {  
30.         LaunchedEffect(Unit) {  
31.             while (true) {  
32.                 delay(autoScrollDuration)  
33.   
34.                 val nextPage = pagerState.currentPage + 1  
35.                 if (nextPage < PAGE_COUNT) {  
36.                     pagerState.animateScrollToPage(nextPage)  
37.                 } else {  
38.                     pagerState.scrollToPage(0)  
39.                 }  
40.             }  
41.         }  
42.     }  
43.   
44.     HorizontalPager(  
45.         state = pagerState,  
46.         modifier = modifier,  
47.     ) { page ->  
48.         pageContent(page.toIndex())  
49.     }  
50. }  

private const val PAGE_COUNT = 10_000 private const val INITIAL_PAGE = PAGE_COUNT / 2 private fun Int.floorMod(other: Int): Int = when (other) { 0 -> this else -> this - this.floorDiv(other) * other } @Composable fun AutoScrollHorizontalPager( itemSize: Int, modifier: Modifier = Modifier, autoScrollDuration: Long = 2_000L, onPageChanged: ((page: Int) -> Unit)? = null, pageContent: @Composable PagerScope.(page: Int) -> Unit, ) { val pagerState = rememberPagerState(INITIAL_PAGE) { PAGE_COUNT } fun Int.toIndex(): Int = (this - INITIAL_PAGE).floorMod(itemSize) if (onPageChanged != null) { LaunchedEffect(onPageChanged) { snapshotFlow { pagerState.currentPage } .collect { page -> onPageChanged(page.toIndex()) } } } val dragged by pagerState.interactionSource.collectIsDraggedAsState() if (!dragged) { LaunchedEffect(Unit) { while (true) { delay(autoScrollDuration) val nextPage = pagerState.currentPage + 1 if (nextPage < PAGE_COUNT) { pagerState.animateScrollToPage(nextPage) } else { pagerState.scrollToPage(0) } } } } HorizontalPager( state = pagerState, modifier = modifier, ) { page -> pageContent(page.toIndex()) } }