hierarchicalFocusGroup

HierarchicalFocusSample

@Sampled
@Composable
fun HierarchicalFocusSample() {
    var selected by remember { mutableIntStateOf(0) }

    Row(Modifier.fillMaxSize(), verticalAlignment = Alignment.CenterVertically) {
        repeat(5) { colIx ->
            Box(
                Modifier.hierarchicalFocusGroup(active = selected == colIx)
                    .weight(1f)
                    .clickable { selected = colIx }
                    .then(
                        if (selected == colIx) {
                            Modifier.border(BorderStroke(2.dp, Color.Red))
                        } else {
                            Modifier
                        }
                    )
            ) {
                // This is used to add a Gray background to the currently focused item, as seen by
                // the focus system.
                var focused by remember { mutableStateOf(false) }

                BasicText(
                    "$colIx",
                    style =
                        TextStyle(
                            color = Color.White,
                            fontSize = 20.sp,
                            textAlign = TextAlign.Center,
                        ),
                    modifier =
                        Modifier.fillMaxWidth()
                            .requestFocusOnHierarchyActive()
                            .onFocusChanged { focused = it.isFocused }
                            .focusable()
                            .then(
                                if (focused) {
                                    Modifier.background(Color.Gray)
                                } else {
                                    Modifier
                                }
                            ),
                )
            }
        }
    }
}

HierarchicalFocus2Levels

@Sampled
@Composable
fun HierarchicalFocus2Levels() {
    Column(Modifier.fillMaxSize()) {
        var selectedRow by remember { mutableIntStateOf(0) }
        repeat(2) { rowIx ->
            Row(
                Modifier.weight(1f)
                    .fillMaxWidth()
                    .hierarchicalFocusGroup(active = selectedRow == rowIx)
            ) {
                var selectedItem by remember { mutableIntStateOf(0) }
                repeat(2) { itemIx ->
                    Box(
                        Modifier.weight(1f).hierarchicalFocusGroup(active = selectedItem == itemIx)
                    ) {
                        // ScalingLazyColumn uses requestFocusOnHierarchyActive internally
                        ScalingLazyColumn(
                            Modifier.fillMaxWidth().clickable {
                                selectedRow = rowIx
                                selectedItem = itemIx
                            }
                        ) {
                            val prefix = (rowIx * 2 + itemIx + 'A'.code).toChar()
                            items(20) {
                                BasicText(
                                    "$prefix $it",
                                    style =
                                        TextStyle(
                                            color = Color.White,
                                            fontSize = 20.sp,
                                            textAlign = TextAlign.Center,
                                        ),
                                )
                            }
                        }
                    }
                }
            }
        }
    }
}