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Builder

class Builder
kotlin.Any
   ↳ androidx.paging.PagedList.Config.Builder

Builder class for PagedList.Config.

You must at minimum specify page size with setPageSize.

Summary

Public constructors

Builder class for PagedList.Config.

Public methods
PagedList.Config

Creates a PagedList.Config with the given parameters.

PagedList.Config.Builder
setEnablePlaceholders(enablePlaceholders: Boolean)

Pass false to disable null placeholders in PagedLists using this PagedList.Config.

PagedList.Config.Builder
setInitialLoadSizeHint(@IntRange(1) initialLoadSizeHint: Int)

Defines how many items to load when first load occurs.

PagedList.Config.Builder
setMaxSize(@IntRange(2) maxSize: Int)

Defines how many items to keep loaded at once.

PagedList.Config.Builder
setPageSize(@IntRange(1) pageSize: Int)

Defines the number of items loaded at once from the PagingSource.

PagedList.Config.Builder
setPrefetchDistance(@IntRange(0) prefetchDistance: Int)

Defines how far from the edge of loaded content an access must be to trigger further loading.

Public constructors

<init>

Builder()

Builder class for PagedList.Config.

You must at minimum specify page size with setPageSize.

Public methods

build

fun build(): PagedList.Config

Creates a PagedList.Config with the given parameters.

Return
A new PagedList.Config.
Exceptions
IllegalArgumentException if placeholders are disabled and prefetchDistance is set to 0
IllegalArgumentException if maximum size is less than pageSize + 2*prefetchDistance

setEnablePlaceholders

fun setEnablePlaceholders(enablePlaceholders: Boolean): PagedList.Config.Builder

Pass false to disable null placeholders in PagedLists using this PagedList.Config.

If not set, defaults to true.

A PagedList will present null placeholders for not-yet-loaded content if two conditions are met:

  1. Its PagingSource can count all unloaded items (so that the number of nulls to present is known).
  2. placeholders are not disabled on the PagedList.Config.

Call setEnablePlaceholders(false) to ensure the receiver of the PagedList (often a androidx.paging.PagedListAdapter) doesn't need to account for null items.

If placeholders are disabled, not-yet-loaded content will not be present in the list. Paging will still occur, but as items are loaded or removed, they will be signaled as inserts to the PagedList.Callback.

PagedList.Callback.onChanged will not be issued as part of loading, though a androidx.paging.PagedListAdapter may still receive change events as a result of PagedList diffing.

Parameters
enablePlaceholders: Boolean false if null placeholders should be disabled.
Return
this

setInitialLoadSizeHint

fun setInitialLoadSizeHint(@IntRange(1) initialLoadSizeHint: Int): PagedList.Config.Builder

Defines how many items to load when first load occurs.

This value is typically larger than page size, so on first load data there's a large enough range of content loaded to cover small scrolls.

If not set, defaults to three times page size.

Parameters
initialLoadSizeHint: Int Number of items to load while initializing the PagedList
Return
this

setMaxSize

fun setMaxSize(@IntRange(2) maxSize: Int): PagedList.Config.Builder

Defines how many items to keep loaded at once.

This can be used to cap the number of items kept in memory by dropping pages. This value is typically many pages so old pages are cached in case the user scrolls back.

This value must be at least two times the prefetchDistance plus the pageSize). This constraint prevent loads from being continuously fetched and discarded due to prefetching.

The max size specified here best effort, not a guarantee. In practice, if maxSize is many times the page size, the number of items held by the PagedList will not grow above this number. Exceptions are made as necessary to guarantee:

  • Pages are never dropped until there are more than two pages loaded. Note that a PagingSource may not be held strictly to requested pageSize, so two pages may be larger than expected.
  • Pages are never dropped if they are within a prefetch window (defined to be pageSize + (2 * prefetchDistance)) of the most recent load.

If not set, defaults to PagedList.Config.Companion.MAX_SIZE_UNBOUNDED, which disables page dropping.

Parameters
maxSize: Int Maximum number of items to keep in memory, or PagedList.Config.Companion.MAX_SIZE_UNBOUNDED to disable page dropping.
Return
this

setPageSize

fun setPageSize(@IntRange(1) pageSize: Int): PagedList.Config.Builder

Defines the number of items loaded at once from the PagingSource.

Should be several times the number of visible items onscreen.

Configuring your page size depends on how your data is being loaded and used. Smaller page sizes improve memory usage, latency, and avoid GC churn. Larger pages generally improve loading throughput, to a point (avoid loading more than 2MB from SQLite at once, since it incurs extra cost).

If you're loading data for very large, social-media style cards that take up most of a screen, and your database isn't a bottleneck, 10-20 may make sense. If you're displaying dozens of items in a tiled grid, which can present items during a scroll much more quickly, consider closer to 100.

Parameters
pageSize: Int Number of items loaded at once from the PagingSource.
Return
this
Exceptions
IllegalArgumentException if pageSize is < 1.

setPrefetchDistance

fun setPrefetchDistance(@IntRange(0) prefetchDistance: Int): PagedList.Config.Builder

Defines how far from the edge of loaded content an access must be to trigger further loading.

Should be several times the number of visible items onscreen.

If not set, defaults to page size.

A value of 0 indicates that no list items will be loaded until they are specifically requested. This is generally not recommended, so that users don't observe a placeholder item (with placeholders) or end of list (without) while scrolling.

Parameters
prefetchDistance: Int Distance the PagedList should prefetch.
Return
this