18. LazyColum 条目的增加和删除


data class Item(
    var item: String,
    var isNew: Boolean,
)

@Composable
fun Item() {

    val context = LocalContext.current
    val list = mutableStateListOf<Item>()

    repeat(20) {
        list.add(Item(item = "Item $it", isNew = false))
    }

    Column(modifier = Modifier
        .fillMaxSize()
        .padding(start = 10.dp, end = 10.dp)) {
        Button(modifier = Modifier
            .fillMaxWidth()
            .padding(top = 10.dp), onClick = {

            val index = (0..5).random()
            if (index < list.size) {
                list.add(index, Item(item = "insert Item ${(0..5).random()}", isNew = true))
            } else {
                list.add(0, Item(item = "insert Item ${(0..5).random()}", isNew = true))
            }

        }) {
            Text(text = "add Item")
        }

        Button(modifier = Modifier
            .fillMaxWidth()
            .padding(top = 10.dp), onClick = {
            val index = (0..5).random()
            if (index < list.size) {
                list.removeAt(index)
            } else {
                Toast.makeText(context, "无此条目", Toast.LENGTH_SHORT).show()
            }
        }) {
            Text(text = "remove Item")
        }

        LazyColumn(content = {
            items(count = list.size, itemContent = { index ->
                Box(modifier = Modifier
                    .fillMaxWidth()
                    .padding(top = 10.dp, bottom = 10.dp)
                    .background(color = if (list[index].isNew) Color.LightGray else Color.DarkGray)) {
                    Text(modifier = Modifier
                        .fillMaxWidth()
                        .padding(top = 10.dp, bottom = 10.dp), fontWeight = FontWeight.Medium, fontSize = 20.sp, color = Color.White, textAlign = TextAlign.Center, text = list[index].item)
                }
            })
        })
    }
}

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