Question: Is there a way to prevent recomposition ...

# compose

[Johnny]

Question: Is there a way to prevent recomposition for a list of Strings from LiveData? When the items are sorted it should not cause recomposition. But seems like observeAsState forces recomposition every time. Even though I’m using key

val value by viewModel.data.observeAsState()

LazyColumn {
    value?.forEach {
        item(key = it) {
            Text( text = "$it!")
        }
    }
}

[Filip Wiesner]

Every LiveData emit will trigger recomposition:

Every time there would be new value posted into the LiveData the returned State will be updated causing recomposition of every State.value usage.

If you don't want your Composable to recompose, make sure the LiveData does not emit new value. I haven't touched LiveData for a while so I don't know how it behaves.
But in the end you shouldn't care about when your component recomposes in most cases. Why do you want to prevent the recomposition?

[divid3d]

You can try to use distinctUntilChanged

[Johnny]

Because it’s unnecessary work done if the data is the same.

This is what intelligent recomposition is meant to prevent. See the MovieOverView example here: https://developer.android.com/jetpack/compose/lifecycle#add-info-smart-recomposition

Even if we add an item to the beginning of the list (shifting all previous items down), because we set a key which maps to the ID of the item, the existing instance should be able to be used. I.e. no recomposition

[Johnny]

@divid3d I probably should have explained the scenario better. It would be new data. It’s just the new data is the sorted list of the original data. And my understanding is re-ordering shouldn’t cause recomposition again. E.g.

// list emitted
banana
apple
orange

// list emitted 2nd time
apple
banana
orange

[Filip Wiesner]

Correct me if I'm wrong but I think key is not really meant to prevent recomposition (even thought it might have that effect sometimes) but rather to keep the same composition instance - e.g. keeping correct instances inside remember.

[Johnny]

Thanks @Filip Wiesner. You’re probably right. I’ll look into this some more

[Csaba Kozák]

https://kotlinlang.slack.com/archives/CJLTWPH7S/p1631631930236700