How to Update the Counter in LazyColumn Items That Are Out of Focus?

Step 1: Use a ViewModel

The first step is to create a ViewModel that will hold the state of your LazyColumn items. This will allow you to update the counter even when the item is out of focus.

@HiltViewModel
class MyViewModel @Inject constructor(private val repository: MyRepository) : ViewModel() {
    private val _counter = MutableLiveData(0)
    val counter: LiveData = _counter

    fun updateCounter() {
        _counter.value = _counter.value?.plus(1)
    }
}

Step 2: Use a key to Identify Items

In your LazyColumn, use a unique key to identify each item. This will allow you to update the correct item even when it’s out of focus.

LazyColumn(
    modifier = Modifier.fillMaxWidth(),
    state = listState
) {
    itemsIndexed(
        items = myList,
        key = { index, item -> item.id }
    ) { _, item ->
        MyItem(item, viewModel)
    }
}

Step 3: Update the Counter

In your MyItem composable, use the ViewModel to update the counter. Since the ViewModel holds the state, it will update the correct item even when it’s out of focus.

@Composable
fun MyItem(item: MyItemModel, viewModel: MyViewModel) {
    Column(
        modifier = Modifier
            .fillMaxWidth()
            .padding(horizontal = 16.dp)
            .padding(vertical = 8.dp)
    ) {
        Text(text = "Counter: ${viewModel.counter.value}")
        Button(onClick = { viewModel.updateCounter() }) {
            Text(text = "Update Counter")
        }
    }
}

Explanation

In the above code, we’ve created a ViewModel that holds the state of the counter. We’ve also used a unique key to identify each item in the LazyColumn. When the user clicks the “Update Counter” button, the ViewModel updates the counter, and since it’s a LiveData, the UI will automatically reflect the change.

Why It Works

The reason this solution works is because the ViewModel holds the state of the counter, and it’s not tied to the Lifecycle of the Composable. Even when the item is out of focus, the ViewModel still holds the correct state, and when the item comes back into focus, the correct state is displayed.

Common Mistakes

When implementing this solution, there are a few common mistakes to avoid:

• Not using a unique key**: If you don’t use a unique key to identify each item, the LazyColumn won’t be able to correctly update the item when it’s out of focus.
• Not using a ViewModel**: If you don’t use a ViewModel to hold the state of the counter, the counter won’t update correctly when the item is out of focus.
• Not using LiveData**: If you don’t use LiveData to observe the state of the counter, the UI won’t automatically update when the counter changes.