Lists và Grids

Hiển thị danh sách và lưới dữ liệu là nhu cầu phổ biến trong ứng dụng. Compose cung cấp các Lazy composables hiệu quả cho việc này.

1. LazyColumn - Danh sách cuộn dọc

Cơ bản

@Composable
fun BasicLazyColumn() {
    LazyColumn {
        items(100) { index ->
            Text(
                text = "Item $index",
                modifier = Modifier
                    .fillMaxWidth()
                    .padding(16.dp)
            )
        }
    }
}

Với danh sách items

@Composable
fun ProductList(products: List<Product>) {
    LazyColumn(
        contentPadding = PaddingValues(16.dp),
        verticalArrangement = Arrangement.spacedBy(8.dp)
    ) {
        items(
            items = products,
            key = { it.id }  // Important: unique key cho mỗi item
        ) { product ->
            ProductCard(product)
        }
    }
}

Mixed content

@Composable
fun MixedContent() {
    LazyColumn {
        item {
            Text("Header", style = MaterialTheme.typography.headlineMedium)
        }

        items(10) { index ->
            Text("Item $index")
        }

        item {
            Text("Section 2", style = MaterialTheme.typography.titleLarge)
        }

        items(5) { index ->
            Text("Section 2 Item $index")
        }

        item {
            Text("Footer")
        }
    }
}

---

2. LazyRow - Danh sách cuộn ngang

@Composable
fun HorizontalCarousel(items: List<CarouselItem>) {
    LazyRow(
        contentPadding = PaddingValues(horizontal = 16.dp),
        horizontalArrangement = Arrangement.spacedBy(8.dp)
    ) {
        items(items, key = { it.id }) { item ->
            Card(
                modifier = Modifier.size(width = 150.dp, height = 200.dp)
            ) {
                Image(
                    painter = painterResource(item.imageRes),
                    contentDescription = item.title,
                    contentScale = ContentScale.Crop,
                    modifier = Modifier.fillMaxSize()
                )
            }
        }
    }
}

---

3. LazyVerticalGrid - Lưới cuộn dọc

Fixed columns

@Composable
fun PhotoGrid(photos: List<Photo>) {
    LazyVerticalGrid(
        columns = GridCells.Fixed(3),  // 3 cột cố định
        contentPadding = PaddingValues(8.dp),
        verticalArrangement = Arrangement.spacedBy(8.dp),
        horizontalArrangement = Arrangement.spacedBy(8.dp)
    ) {
        items(photos, key = { it.id }) { photo ->
            AsyncImage(
                model = photo.url,
                contentDescription = null,
                modifier = Modifier.aspectRatio(1f),
                contentScale = ContentScale.Crop
            )
        }
    }
}

Adaptive columns

@Composable
fun AdaptiveGrid(items: List<Item>) {
    LazyVerticalGrid(
        columns = GridCells.Adaptive(minSize = 128.dp),  // Tự điều chỉnh số cột
        contentPadding = PaddingValues(16.dp),
        verticalArrangement = Arrangement.spacedBy(8.dp),
        horizontalArrangement = Arrangement.spacedBy(8.dp)
    ) {
        items(items, key = { it.id }) { item ->
            ItemCard(item)
        }
    }
}

---

4. LazyVerticalStaggeredGrid - Lưới so le

@Composable
fun PinterestStyleGrid(items: List<PinItem>) {
    LazyVerticalStaggeredGrid(
        columns = StaggeredGridCells.Fixed(2),
        contentPadding = PaddingValues(8.dp),
        verticalItemSpacing = 8.dp,
        horizontalArrangement = Arrangement.spacedBy(8.dp)
    ) {
        items(items, key = { it.id }) { item ->
            PinCard(
                item = item,
                modifier = Modifier.fillMaxWidth()  // Height tự động theo content
            )
        }
    }
}

@Composable
fun PinCard(item: PinItem, modifier: Modifier = Modifier) {
    Card(modifier = modifier) {
        Column {
            AsyncImage(
                model = item.imageUrl,
                contentDescription = null,
                modifier = Modifier
                    .fillMaxWidth()
                    .aspectRatio(item.aspectRatio)  // Mỗi item có ratio khác nhau
            )
            Text(item.title, modifier = Modifier.padding(8.dp))
        }
    }
}

---

5. Key và ContentType - Performance

Sử dụng key

Key giúp Compose identify items đúng khi list thay đổi:

@Composable
fun KeyExample(items: List<Item>) {
    LazyColumn {
        items(
            items = items,
            key = { it.id }  // Unique, stable ID
        ) { item ->
            ItemRow(item)
        }
    }
}

Sử dụng contentType

contentType giúp optimize composition khi có nhiều loại items:

@Composable
fun MixedList(feed: List<FeedItem>) {
    LazyColumn {
        items(
            items = feed,
            key = { it.id },
            contentType = { item ->
                when (item) {
                    is FeedItem.Header -> "header"
                    is FeedItem.Post -> "post"
                    is FeedItem.Ad -> "ad"
                }
            }
        ) { item ->
            when (item) {
                is FeedItem.Header -> HeaderCard(item)
                is FeedItem.Post -> PostCard(item)
                is FeedItem.Ad -> AdCard(item)
            }
        }
    }
}

---

6. Sticky Headers

@OptIn(ExperimentalFoundationApi::class)
@Composable
fun ContactList(contacts: Map<Char, List<Contact>>) {
    LazyColumn {
        contacts.forEach { (letter, contactsForLetter) ->
            stickyHeader {
                Text(
                    text = letter.toString(),
                    modifier = Modifier
                        .fillMaxWidth()
                        .background(MaterialTheme.colorScheme.surfaceVariant)
                        .padding(16.dp),
                    style = MaterialTheme.typography.titleMedium
                )
            }

            items(contactsForLetter, key = { it.id }) { contact ->
                ContactRow(contact)
            }
        }
    }
}

---

7. Scroll State và Control

Observing Scroll Position

@Composable
fun ScrollAwareList() {
    val listState = rememberLazyListState()

    // Kiểm tra có scroll được không
    val isScrolled = listState.firstVisibleItemIndex > 0

    // Observe scroll position
    LaunchedEffect(listState) {
        snapshotFlow { listState.firstVisibleItemIndex }
            .collect { index ->
                println("First visible item: $index")
            }
    }

    LazyColumn(state = listState) {
        items(100) { index ->
            Text("Item $index")
        }
    }
}

Programmatic Scrolling

@Composable
fun ScrollToTopExample() {
    val listState = rememberLazyListState()
    val scope = rememberCoroutineScope()

    val showButton by remember {
        derivedStateOf { listState.firstVisibleItemIndex > 0 }
    }

    Box {
        LazyColumn(state = listState) {
            items(100) { Text("Item $it") }
        }

        if (showButton) {
            FloatingActionButton(
                onClick = {
                    scope.launch {
                        listState.animateScrollToItem(0)
                    }
                },
                modifier = Modifier
                    .align(Alignment.BottomEnd)
                    .padding(16.dp)
            ) {
                Icon(Icons.Default.KeyboardArrowUp, null)
            }
        }
    }
}

---

8. Pull to Refresh

@OptIn(ExperimentalMaterial3Api::class)
@Composable
fun RefreshableList(
    items: List<Item>,
    onRefresh: suspend () -> Unit
) {
    val refreshState = rememberPullToRefreshState()
    var isRefreshing by remember { mutableStateOf(false) }

    if (refreshState.isRefreshing) {
        LaunchedEffect(true) {
            isRefreshing = true
            onRefresh()
            isRefreshing = false
            refreshState.endRefresh()
        }
    }

    Box(
        modifier = Modifier
            .fillMaxSize()
            .nestedScroll(refreshState.nestedScrollConnection)
    ) {
        LazyColumn {
            items(items) { item ->
                ItemRow(item)
            }
        }

        PullToRefreshContainer(
            state = refreshState,
            modifier = Modifier.align(Alignment.TopCenter)
        )
    }
}

---

9. Paging với Compose

Setup

build.gradle.kts

dependencies {
    implementation("androidx.paging:paging-compose:3.3.0")
}

Sử dụng

@Composable
fun PagedList(viewModel: MyViewModel) {
    val lazyPagingItems = viewModel.pagingData.collectAsLazyPagingItems()

    LazyColumn {
        items(
            count = lazyPagingItems.itemCount,
            key = lazyPagingItems.itemKey { it.id }
        ) { index ->
            val item = lazyPagingItems[index]
            item?.let { ItemRow(it) }
        }

        // Loading indicator
        when (lazyPagingItems.loadState.append) {
            is LoadState.Loading -> {
                item {
                    CircularProgressIndicator(
                        modifier = Modifier
                            .fillMaxWidth()
                            .padding(16.dp)
                            .wrapContentWidth(Alignment.CenterHorizontally)
                    )
                }
            }
            is LoadState.Error -> {
                item {
                    Button(onClick = { lazyPagingItems.retry() }) {
                        Text("Retry")
                    }
                }
            }
            else -> {}
        }
    }
}

---

10. Item Animations

AnimatedVisibility cho items

@Composable
fun AnimatedItemList(items: List<Item>) {
    LazyColumn {
        items(items, key = { it.id }) { item ->
            var visible by remember { mutableStateOf(false) }

            LaunchedEffect(Unit) {
                visible = true
            }

            AnimatedVisibility(
                visible = visible,
                enter = fadeIn() + slideInVertically(),
                exit = fadeOut() + slideOutVertically()
            ) {
                ItemRow(item)
            }
        }
    }
}

Swipe to Dismiss

@OptIn(ExperimentalMaterial3Api::class)
@Composable
fun SwipeableItem(
    item: Item,
    onDismiss: () -> Unit
) {
    val dismissState = rememberSwipeToDismissBoxState(
        confirmValueChange = {
            if (it == SwipeToDismissBoxValue.EndToStart) {
                onDismiss()
                true
            } else {
                false
            }
        }
    )

    SwipeToDismissBox(
        state = dismissState,
        backgroundContent = {
            Box(
                modifier = Modifier
                    .fillMaxSize()
                    .background(Color.Red)
                    .padding(16.dp),
                contentAlignment = Alignment.CenterEnd
            ) {
                Icon(Icons.Default.Delete, null, tint = Color.White)
            }
        }
    ) {
        ItemCard(item)
    }
}

---

📝 Tóm tắt

Component	Mục đích
LazyColumn	Danh sách cuộn dọc
LazyRow	Danh sách cuộn ngang
LazyVerticalGrid	Lưới cuộn dọc
LazyHorizontalGrid	Lưới cuộn ngang
LazyVerticalStaggeredGrid	Lưới so le (Pinterest style)

Best Practices

• Luôn sử dụng key với unique, stable ID
• Dùng contentType khi có nhiều loại items
• Tránh làm composable trong items quá nặng
• Sử dụng derivedStateOf cho derived scroll values
• Dùng Paging 3 cho large datasets