Posted this originally in compose-android but got ...

# compose

[Jerry Johns]

Posted this originally in compose-android but got no takers, so posting here in the hopes it will have someone who might!

We have the following bit of logic:

@Composable
fun PanelContent(
  viewModel: ArticlesViewModel,
  magazine: ArticlesViewModel.MagazineState,
  onShowSnackbar: (String) -> Unit,
) {
  val articlesState by
    remember(viewModel, articles) { viewModel.getArticlesState(magazine) }
      .collectAsStateWithLifecycle()

  articlesState?: return

  LazyVerticalGrid(
    columns = GridCells.Adaptive(minSize = 128.dp),
    Modifier.absolutePadding(top = 8.dp, left = 16.dp, right = 16.dp, bottom = 8.dp).fillMaxSize(),
    verticalArrangement = Arrangement.spacedBy(8.dp),
    horizontalArrangement = Arrangement.spacedBy(8.dp),
  ) {
     val articles = articlesState!!.map { it.articleInfo }.toSet()
     ...

getArticlesState returns back a StateFlow<Collection<ArticlesState>?> . The null indicates the absence of any real value from our backend repository.

I'm observing that sometimes, I get a `NullPointerException`at articlesState!! when it re-composes. How is that possible? Wouldn't the null check earlier have tripped?

[Sean Proctor]

No, because the second reference is in a lambda.

[Sean Proctor]

You could set a local variable to articleState and check that value is non-null. Then the compiler could give you a guarantee and you wouldn't need the unsafe reference.

[Albert Chang]

I would suggest filing a bug and in the meantime you can just use articlesState?.let { LazyVerticalGrid() }.

[Albert Chang]

There used to be several subtle bugs related to early return in composable functions. I think most of them have been fixed, but there might be more.

[Jerry Johns]

Thanks for the tips! I ended up creating the non-null local variable, that did the trick!!