Jetpack Compose Lazy Column single selection

Question

I'm getting data from the server and displaying it in the list, each item can be selected with one click to display the button, but I cannot close it, I can only open it.

This is item of list class

data class Task( val deviceName: String, val deviceId: String, var selected :Boolean= Boolean, )

this is data class

data class TaskStatus( val taskList: SnapshotStateList<Task> = SnapshotStateList(), val selectedNumber: Int = -1, )

My ViewModel

private val _status = MutableStateFlow(TaskStatus()) val status = _status.asStateFlow() fun getList(){ ... for(item in result){ _status.value.taskList.add(task) } } fun selectTask(task: Task) { val list = _status.value.taskList val selectNumber = _status.value.selectedNumber val newSelectNumber = list.indexOf(task) if (newSelectNumber != selectNumber) { if (selectNumber != -1) { list[selectNumber].selected.value = false } } task.selected.value = !task.selected.value _status.update { it.copy(selectedNumber = newSelectNumber) } }

My LazyColumn

... LazyColumn( modifier = Modifier .fillMaxWidth() .weight(1F), verticalArrangement = Arrangement.spacedBy(11.dp), contentPadding = PaddingValues(16.dp) ) { items( taskStatus.taskList, key = { it.deviceId }) { task -> Item(task) } } @Compose fun Item(task:Task){ Column(){ Text(text = task.name) Text(text = task.deviceId) if(task.selected){ Botton() } } }

I can only show but not hide the button

Thank you in advance.

z.g.y · Accepted Answer · 2022-10-22 15:48:22Z

I can't compile your code directly so I tried to make my own implementation. I added a callback which will be triggered from your Task Item

Your TaskList composable

@Composable fun TaskList( taskList: SnapshotStateList<Task>, onSelected: (Task) -> Unit ) { LazyColumn( modifier = Modifier .fillMaxWidth(), verticalArrangement = Arrangement.spacedBy(11.dp), contentPadding = PaddingValues(16.dp) ) { items( taskList, key = { it.deviceId }) { task -> Item(task) { onSelected(it) } } } }

Your TaskItem Composable

@Composable fun Item( task:Task, onSelected: (Task) -> Unit ){ Column( modifier = Modifier.clickable { onSelected(task) // selection callback } ){ Text(text = task.deviceName) Text(text = task.deviceId) if(task.selected) { Box(modifier = Modifier .fillMaxWidth() .height(100.dp) .background(Color.Red)) { } } } }

And I mocked a VieModel

class TaskStateHolder { private val _status = MutableStateFlow( TaskStatus ( taskList = mutableStateListOf( Task( deviceName = "Device 1", deviceId = "Device 1 ID" ), Task( deviceName = "Device 2", deviceId = "Device 2 ID" ), Task( deviceName = "Device 3", deviceId = "Device 3 ID" ), Task( deviceName = "Device 4", deviceId = "Device 4 ID" ), ) )) val status = _status.asStateFlow() fun selectTask(task: Task) { _status.update { val list = it.taskList val newSelectNumber = list.indexOf(task) val iterator = list.listIterator() while (iterator.hasNext()) { val obj = iterator.next() if (task.deviceId == obj.deviceId) { iterator.set(task.copy(selected = true)) } else { iterator.set(obj.copy(selected = false)) } } it.copy(selectedNumber = newSelectNumber) } } }

I modified your selectedTask function, executing _status flow udpates in a single pass using the list's iterator.

Usage somewhere outside (e.g "TaskScreen")

val tasks by stateHolder.status.collectAsState() Column { TaskList(tasks.taskList) { stateHolder.selectTask(it) } }

Thank you for your answer. I've tried your method, but I'm sorry I didn't make it clear. I mean, the data has changed but the display has not changed. I can't even use your method. I can expand every item, but if you want to expand one of them, the other will be closed
I tried my own implementation using the available codes you posted, please see the updated answer and the .gif showing single selection
Thank you very much for your answer. I have completed the functions I need and optimized the code you gave me. I will selectedNumber -> selectId
thanks again,I have some small problems How long will the data of the viewmodel remain? If two identical viewmodels are created, will the data be the same? Maybe I should send another question

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