Gestures

Xử lý touch input và gestures là một phần quan trọng của mobile UI. Compose cung cấp APIs trực quan để detect và phản hồi các gestures.

1. Click và Tap cơ bản

clickable modifier

@Composable
fun ClickableBox() {
    Box(
        modifier = Modifier
            .size(100.dp)
            .background(Color.Blue)
            .clickable {
                println("Clicked!")
            }
    )
}

clickable với parameters

@Composable
fun AccessibleButton() {
    Box(
        modifier = Modifier
            .size(100.dp)
            .background(Color.Blue)
            .clickable(
                enabled = true,
                onClick = { },
                role = Role.Button,
                onClickLabel = "Perform action"  // For accessibility
            )
    )
}

combinedClickable

@Composable
fun MultiClickBox() {
    Box(
        modifier = Modifier
            .size(100.dp)
            .background(Color.Blue)
            .combinedClickable(
                onClick = { println("Single click") },
                onDoubleClick = { println("Double click") },
                onLongClick = { println("Long press") }
            )
    )
}

---

2. Pointer Input - Low-level API

detectTapGestures

@Composable
fun TapGesturesBox() {
    Box(
        modifier = Modifier
            .size(100.dp)
            .background(Color.Blue)
            .pointerInput(Unit) {
                detectTapGestures(
                    onTap = { offset ->
                        println("Tap at $offset")
                    },
                    onDoubleTap = { offset ->
                        println("Double tap at $offset")
                    },
                    onLongPress = { offset ->
                        println("Long press at $offset")
                    },
                    onPress = { offset ->
                        // Called immediately when pressed
                        val released = tryAwaitRelease()
                        if (released) {
                            println("Released")
                        } else {
                            println("Cancelled")
                        }
                    }
                )
            }
    )
}

---

3. Scroll

verticalScroll / horizontalScroll

@Composable
fun ScrollableContent() {
    val scrollState = rememberScrollState()

    Column(
        modifier = Modifier
            .fillMaxSize()
            .verticalScroll(scrollState)
    ) {
        repeat(50) { index ->
            Text("Item $index", modifier = Modifier.padding(16.dp))
        }
    }
}

Programmatic scrolling

@Composable
fun ControlledScroll() {
    val scrollState = rememberScrollState()
    val scope = rememberCoroutineScope()

    Column {
        Button(onClick = {
            scope.launch {
                scrollState.animateScrollTo(0)  // Scroll to top
            }
        }) {
            Text("Scroll to Top")
        }

        Column(modifier = Modifier.verticalScroll(scrollState)) {
            // Content
        }
    }
}

Observe scroll position

@Composable
fun ScrollObserver() {
    val scrollState = rememberScrollState()

    LaunchedEffect(scrollState) {
        snapshotFlow { scrollState.value }
            .collect { scrollPosition ->
                println("Scroll position: $scrollPosition")
            }
    }

    Column(modifier = Modifier.verticalScroll(scrollState)) {
        // Content
    }
}

---

4. Drag

draggable modifier

@Composable
fun DraggableBox() {
    var offsetX by remember { mutableStateOf(0f) }

    Box(
        modifier = Modifier
            .offset { IntOffset(offsetX.roundToInt(), 0) }
            .size(100.dp)
            .background(Color.Blue)
            .draggable(
                orientation = Orientation.Horizontal,
                state = rememberDraggableState { delta ->
                    offsetX += delta
                }
            )
    )
}

detectDragGestures - 2D drag

@Composable
fun FreeDraggableBox() {
    var offset by remember { mutableStateOf(Offset.Zero) }

    Box(
        modifier = Modifier
            .offset { IntOffset(offset.x.roundToInt(), offset.y.roundToInt()) }
            .size(100.dp)
            .background(Color.Blue)
            .pointerInput(Unit) {
                detectDragGestures { change, dragAmount ->
                    change.consume()
                    offset += dragAmount
                }
            }
    )
}

Drag với animation

@Composable
fun SnapBackDraggable() {
    var offset by remember { mutableStateOf(Offset.Zero) }

    val animatedOffset by animateOffsetAsState(
        targetValue = offset,
        animationSpec = spring(stiffness = Spring.StiffnessLow),
        label = "offset"
    )

    Box(
        modifier = Modifier
            .offset { IntOffset(animatedOffset.x.roundToInt(), animatedOffset.y.roundToInt()) }
            .size(100.dp)
            .background(Color.Blue)
            .pointerInput(Unit) {
                detectDragGestures(
                    onDragEnd = {
                        offset = Offset.Zero  // Snap back
                    }
                ) { change, dragAmount ->
                    change.consume()
                    offset += dragAmount
                }
            }
    )
}

---

5. Swipe

Swipe to Dismiss

@OptIn(ExperimentalMaterial3Api::class)
@Composable
fun SwipeItem(onDismiss: () -> Unit) {
    val dismissState = rememberSwipeToDismissBoxState(
        confirmValueChange = { value ->
            if (value == SwipeToDismissBoxValue.EndToStart) {
                onDismiss()
                true
            } else {
                false
            }
        }
    )

    SwipeToDismissBox(
        state = dismissState,
        backgroundContent = {
            Box(
                modifier = Modifier
                    .fillMaxSize()
                    .background(Color.Red),
                contentAlignment = Alignment.CenterEnd
            ) {
                Icon(
                    Icons.Default.Delete, null,
                    modifier = Modifier.padding(16.dp),
                    tint = Color.White
                )
            }
        }
    ) {
        Card {
            Text("Swipe to delete", modifier = Modifier.padding(16.dp))
        }
    }
}

Custom Swipe Detection

@Composable
fun CustomSwipe() {
    var offsetX by remember { mutableStateOf(0f) }
    var swiped by remember { mutableStateOf(false) }

    val animatedOffset by animateFloatAsState(
        targetValue = if (swiped) 500f else offsetX,
        label = "swipe"
    )

    Box(
        modifier = Modifier
            .offset { IntOffset(animatedOffset.roundToInt(), 0) }
            .fillMaxWidth()
            .height(60.dp)
            .background(Color.Blue)
            .pointerInput(Unit) {
                detectHorizontalDragGestures(
                    onDragEnd = {
                        if (abs(offsetX) > 200) {
                            swiped = true
                        } else {
                            offsetX = 0f
                        }
                    }
                ) { change, dragAmount ->
                    change.consume()
                    offsetX += dragAmount
                }
            }
    ) {
        Text("Swipe me", color = Color.White)
    }
}

---

6. Transform Gestures - Zoom, Rotate, Pan

@Composable
fun TransformableImage() {
    var scale by remember { mutableStateOf(1f) }
    var rotation by remember { mutableStateOf(0f) }
    var offset by remember { mutableStateOf(Offset.Zero) }

    val state = rememberTransformableState { zoomChange, offsetChange, rotationChange ->
        scale *= zoomChange
        rotation += rotationChange
        offset += offsetChange
    }

    Image(
        painter = painterResource(R.drawable.image),
        contentDescription = null,
        modifier = Modifier
            .graphicsLayer(
                scaleX = scale,
                scaleY = scale,
                rotationZ = rotation,
                translationX = offset.x,
                translationY = offset.y
            )
            .transformable(state = state)
            .fillMaxSize()
    )
}

detectTransformGestures (low-level)

@Composable
fun ManualTransform() {
    var scale by remember { mutableStateOf(1f) }
    var rotation by remember { mutableStateOf(0f) }
    var offset by remember { mutableStateOf(Offset.Zero) }

    Box(
        modifier = Modifier
            .graphicsLayer(
                scaleX = scale,
                scaleY = scale,
                rotationZ = rotation,
                translationX = offset.x,
                translationY = offset.y
            )
            .pointerInput(Unit) {
                detectTransformGestures { centroid, pan, zoom, rotationDelta ->
                    scale *= zoom
                    rotation += rotationDelta
                    offset += pan
                }
            }
            .size(200.dp)
            .background(Color.Blue)
    )
}

---

7. Nested Scrolling

nestedScroll modifier

@OptIn(ExperimentalMaterial3Api::class)
@Composable
fun CollapsibleToolbar() {
    val scrollBehavior = TopAppBarDefaults.exitUntilCollapsedScrollBehavior()

    Scaffold(
        modifier = Modifier.nestedScroll(scrollBehavior.nestedScrollConnection),
        topBar = {
            LargeTopAppBar(
                title = { Text("Title") },
                scrollBehavior = scrollBehavior
            )
        }
    ) { padding ->
        LazyColumn(modifier = Modifier.padding(padding)) {
            items(100) { index ->
                Text("Item $index", modifier = Modifier.padding(16.dp))
            }
        }
    }
}

---

8. Accessibility và Gestures

@Composable
fun AccessibleGestures() {
    Box(
        modifier = Modifier
            .size(100.dp)
            .background(Color.Blue)
            .semantics {
                onClick(label = "Perform main action") {
                    // Handle click for accessibility
                    true
                }
                onLongClick(label = "Show menu") {
                    // Handle long click
                    true
                }
            }
            .pointerInput(Unit) {
                detectTapGestures(
                    onTap = { /* Regular tap */ },
                    onLongPress = { /* Regular long press */ }
                )
            }
    )
}

---

9. Custom Gesture Detector

suspend fun PointerInputScope.detectTripleTap(
    onTripleTap: (Offset) -> Unit
) {
    awaitEachGesture {
        val firstDown = awaitFirstDown()
        val firstUp = waitForUpOrCancellation()
        if (firstUp == null || (firstUp.uptimeMillis - firstDown.uptimeMillis) > 200) return@awaitEachGesture

        val secondDown = withTimeoutOrNull(300) { awaitFirstDown() }
        if (secondDown == null) return@awaitEachGesture
        val secondUp = waitForUpOrCancellation()
        if (secondUp == null) return@awaitEachGesture

        val thirdDown = withTimeoutOrNull(300) { awaitFirstDown() }
        if (thirdDown == null) return@awaitEachGesture
        val thirdUp = waitForUpOrCancellation()
        if (thirdUp != null) {
            onTripleTap(thirdUp.position)
        }
    }
}

@Composable
fun TripleTapBox() {
    Box(
        modifier = Modifier
            .size(100.dp)
            .background(Color.Blue)
            .pointerInput(Unit) {
                detectTripleTap { offset ->
                    println("Triple tap at $offset")
                }
            }
    )
}

---

📝 Tóm tắt

Gesture	API
Tap	clickable, detectTapGestures
Long Press	combinedClickable, detectTapGestures
Scroll	verticalScroll, horizontalScroll
Drag	draggable, detectDragGestures
Swipe	SwipeToDismissBox, custom
Transform	transformable, detectTransformGestures

Chọn API nào?

Cần đơn giản?
├── Click → clickable
├── Multiple click types → combinedClickable
└── Scroll → verticalScroll/horizontalScroll

Cần customize?
└── pointerInput + detect*Gestures