The initial purpose is to understand how the prepend loading in Paging3 is triggered, is it able to manually triggered with flexibility, and it extended to get to know the whole lib well.
Although Paging3 is a complicate Android lib with a bunch of classes to do the paging stuff, the NotebookLM helps explain the concept well. By pasting all the source code to it as context, it explains the concept and the relationship between core classes, and draws the diagram for me.
Preparation #
- Download all the paging3 source code using https://downgit.github.io/#/home
- Paging3 common lib source code: https://github.com/androidx/androidx/tree/androidx-main/paging/paging-common/src/commonMain/kotlin/androidx/paging
- Use copy-files-to-clipboard-for-llm plugin to merge all the files and copy to clipboard
- Paste the source code to NotebookLM as the reference source
- Chat with NotebookLM to get explanation and diagrams
Sequence Diagram #
sequenceDiagram
participant UI
participant LazyPagingItems
participant PagingDataPresenter
participant HintReceiver
participant PageFetcher
participant PageFetcherSnapshot
participant PageFetcherSnapshotState
participant PagingSource
UI->>LazyPagingItems: Access item (get)
activate UI
activate LazyPagingItems
LazyPagingItems->>PagingDataPresenter: Get item at index (get)
activate PagingDataPresenter
PagingDataPresenter->>PagingDataPresenter: Get item from page store
PagingDataPresenter->>HintReceiver: Access Hint (ViewportHint)
deactivate UI
activate HintReceiver
HintReceiver->>PageFetcher: Access Hint (ViewportHint)
deactivate HintReceiver
activate PageFetcher
PageFetcher->>PageFetcherSnapshot: Access Hint (ViewportHint)
activate PageFetcherSnapshot
PageFetcherSnapshot->>PageFetcherSnapshot: Wrap hint with generationId (GenerationalViewportHint)
PageFetcherSnapshot->>PageFetcherSnapshotState: Get next load key (nextLoadKeyOrNull)
activate PageFetcherSnapshotState
PageFetcherSnapshotState-->>PageFetcherSnapshot: Return load key
deactivate PageFetcherSnapshotState
alt Valid load key and prefetch distance not fulfilled
PageFetcherSnapshot->>PagingSource: Load data (load, LoadParams{loadType=PREPEND, key, loadSize})
activate PagingSource
PagingSource->>PagingSource: Fetch data
PagingSource-->>PageFetcherSnapshot: Load result (LoadResult{Page/Error})
deactivate PagingSource
PageFetcherSnapshot->>PageFetcherSnapshotState: Insert page, update load state, check for drop (insert)
activate PageFetcherSnapshotState
PageFetcherSnapshotState-->>PageFetcherSnapshot: Confirmation
deactivate PageFetcherSnapshotState
else Load key invalid or prefetch distance fulfilled
PageFetcherSnapshot->>PageFetcherSnapshot: Skip load
end
deactivate PageFetcherSnapshot
deactivate PageFetcher
deactivate PagingDataPresenter
LazyPagingItems-->>UI: Return item
deactivate LazyPagingItemsCore components #
classDiagram
class UI
class LazyPagingItems {
-flow: Flow<PagingData<T>>
-pagingDataPresenter: PagingDataPresenter<T>
+refresh()
+loadState: CombinedLoadStates
+get(index: Int): T?
}
class PagingDataPresenter {
-hintReceiver: HintReceiver
-uiReceiver: UiReceiver
-pageStore: PageStore
+refresh()
+get(index: Int) : T?
+addLoadStateListener(listener)
+removeLoadStateListener(listener)
+presentPagingDataEvent(event: PagingDataEvent)
}
class HintReceiver {
+accessHint(hint: ViewportHint)
}
class PageFetcher {
-snapshot: PageFetcherSnapshot
+refresh()
}
class PageFetcherSnapshot {
-pagingSource: PagingSource
-stateHolder: PageFetcherSnapshotState.Holder
+doLoad(loadType: LoadType, hint: GenerationalViewportHint)
+doInitialLoad()
}
class PageFetcherSnapshotState {
-pages: List<TransformablePage<Key, Value>>
-placeholdersBefore: Int
-placeholdersAfter: Int
+insert(generationId: Int, loadType: LoadType, page: Page) : Boolean
+nextLoadKeyOrNull(loadType: LoadType, generationId: Int, presentedItemsBeyondAnchor: Int) : Key?
}
class PagingSource {
+load(params: LoadParams) : LoadResult
}
UI ..> LazyPagingItems
LazyPagingItems *-- PagingDataPresenter
PagingDataPresenter ..> HintReceiver
HintReceiver ..> PageFetcher
PageFetcher *-- PageFetcherSnapshot
PageFetcherSnapshot *-- PageFetcherSnapshotState
PageFetcherSnapshot ..> PagingSource