一、前言

该功能是一个左侧为字符索引列表，右侧为联系人列表的实现，点击左侧字符索引可以自动滑动到对应联系人条目。该功能代码实现绝大多数有通义灵码完成。实现效果如下：

关键代码

data class Contact(val name: String)

class ContactsPage {
    val contacts = listOf(
        Contact("Alice"),
        Contact("Bob"),
        Contact("Charlie"),
        Contact("David"),
        Contact("Eve"),
        Contact("Frank"),
        Contact("Grace"),
        Contact("Heidi"),
        Contact("Ivan"),
        Contact("John"),
        Contact("Karen"),
        Contact("Larry"),
        Contact("Mary"),
        Contact("Nancy"),
        Contact("Olivia"),
        Contact("Paul"),
        Contact("Quincy"),
        Contact("Rachel"),
        Contact("Steve"),
        Contact("Tom"),
        Contact("Ursula"),
        Contact("Victor"),
        Contact("Wendy"),
        Contact("Xavier"),
        Contact("Yolanda"),
        Contact("Zoe")
    )

    fun alphabetIndexer(contact: Contact) = contact.name.first().toString().uppercase()

    @Composable
    fun IndexedContactsList(contacts: List<Contact>) {
        val indexer = { contact: Contact -> alphabetIndexer(contact) }
        val sections = contacts.groupBy(indexer)
        val entries = sections.entries.toList()

        // 记录每个字母索引的位置
        val letterPositions = remember { mutableMapOf<String, Int>() }
        val listState = remember { LazyListState() }

        // 计算每个字母索引的位置
        var currentLetter = ""
        for ((position, contact) in contacts.withIndex()) {
            val letter = indexer(contact)
            if (letter != currentLetter) {
                letterPositions[letter] = position
                currentLetter = letter
            }
        }
        val coroutineScope = rememberCoroutineScope()
        Row(
            modifier = Modifier.fillMaxSize()
        ) {
            // 右侧字母索引列表
            LazyColumn(
                modifier = Modifier
                    .weight(0.2f) // 设置宽度比例
                    .fillMaxHeight()
                    .padding(8.dp)
            ) {
                itemsIndexed(entries) { index, entry ->
                    Text(
                        text = entry.key,
                        modifier = Modifier
                            .fillMaxWidth()
                            .clickable {
                                /* Handle click */
                                // 点击字母索引时滚动到对应位置
                                coroutineScope.launch {
                                    listState.animateScrollToItem(letterPositions[entry.key] ?: 0)
                                }
                            }
                            .padding(vertical = 8.dp),
                        style = MaterialTheme.typography.subtitle1,
                        color = Color.Gray
                    )
                }
            }

            // 左侧联系人列表
            LazyColumn(
                state = listState,
                modifier = Modifier
                    .weight(0.8f) // 设置宽度比例
                    .fillMaxHeight()
                    .padding(8.dp)
            ) {
                itemsIndexed(contacts) { index, contact ->
                    val letter = indexer(contact)
                    if (index == 0 || indexer(contacts[index - 1]) != letter) {
                        Text(
                            text = letter,
                            modifier = Modifier.padding(
                                start = 16.dp,
                                top = 8.dp,
                                end = 16.dp,
                                bottom = 4.dp
                            ),
                            style = MaterialTheme.typography.subtitle1,
                            color = Color.Gray
                        )
                    }
                    Text(
                        text = contact.name,
                        modifier = Modifier
                            .fillMaxWidth()
                            .clickable { /* Handle click */ }
                            .padding(horizontal = 16.dp, vertical = 8.dp),
                        style = MaterialTheme.typography.body1
                    )
                }
            }
        }
    }

    @Preview(showBackground = true)
    @Composable
    fun PreviewIndexedContactsList() {
        MaterialTheme {
            IndexedContactsList(contacts)
        }
    }
}