Skip to main content

Paging load states, retry, empty UI, and recreation

Load state exists per load type and source (source PagingSource, mediator RemoteMediator). Combined states require deliberate UI policy.

when {
    items.loadState.refresh is LoadState.Loading && items.itemCount == 0 -> FullScreenLoading()
    items.loadState.refresh is LoadState.Error && items.itemCount == 0 -> FullScreenError(onRetry = items::retry)
    items.itemCount == 0 && items.loadState.refresh is LoadState.NotLoading -> EmptyState()
    else -> ProductList(items)
}

Append loading/error belongs footer; refresh with existing content can show pull indicator/banner instead of replacing content.

Source versus mediator​

With Room + RemoteMediator, source may successfully display cached rows while mediator refresh fails. UI should retain rows and show “Could not update.” Checking only combined refresh without understanding origin can hide useful data.

Retry versus refresh​

  • retry() retries failed load with same generation/params.
  • refresh() invalidates current generation and creates new initial load.

User retry after transient append error should call retry. Changed query/account/sort needs new Pager/generation. Pull-to-refresh invokes refresh and repository freshness behavior.

Empty correctness​

Do not declare empty while refresh still loading. Placeholder count can make itemCount nonzero with null items. Remote mediator might be loading even after local source initially returns empty.

Process recreation​

ViewModel + cachedIn handles configuration, not process death. Room-backed Pager recreates from DB; saved query/filter/selected anchor reconstructs. Network-only Paging reloads; exact in-memory page state is not durable.

Scroll restoration needs stable keys/order and saveable LazyList state. Restored index can point to different entity after sync; anchor by ID when product requires exact continuity.

Error messages​

Map exceptions into user recovery without exposing raw HTTP. Preserve retry eligibility. Authentication error routes through session policy; schema error should not retry endlessly.

UX rule

Load state answers “which operation/source is doing what?” Combine it with whether usable items exist. That yields full-screen, inline, footer, or silent behavior.

Exercises​

  1. Render cached data while mediator refresh fails.
  2. Choose retry versus refresh in six cases.
  3. Avoid false empty state during mediator load.