PageKeyedDataSource

<init>

PageKeyedDataSource()

Incremental data loader for page-keyed content, where requests return keys for next/previous pages.

Implement a DataSource using PageKeyedDataSource if you need to use data from page N - 1 to load page N. This is common, for example, in network APIs that include a next/previous link or key with each page load.

The InMemoryByPageRepository in the PagingWithNetworkSample shows how to implement a network PageKeyedDataSource using Retrofit, while handling swipe-to-refresh, network errors, and retry.

loadAfter

abstract fun loadAfter(
    @NonNull params: PageKeyedDataSource.LoadParams<Key>, 
    @NonNull callback: PageKeyedDataSource.LoadCallback<Key, Value>
): Unit

Append page with the key specified by LoadParams.key.

It's valid to return a different list size than the page size if it's easier, e.g. if your backend defines page sizes. It is generally safer to increase the number loaded than reduce.

Data may be passed synchronously during the load method, or deferred and called at a later time. Further loads going down will be blocked until the callback is called.

If data cannot be loaded (for example, if the request is invalid, or the data would be stale and inconsistent, it is valid to call invalidate() to invalidate the data source, and prevent further loading.

loadBefore

abstract fun loadBefore(
    @NonNull params: PageKeyedDataSource.LoadParams<Key>, 
    @NonNull callback: PageKeyedDataSource.LoadCallback<Key, Value>
): Unit

Prepend page with the key specified by LoadParams.key.

It's valid to return a different list size than the page size if it's easier, e.g. if your backend defines page sizes. It is generally safer to increase the number loaded than reduce.

Data may be passed synchronously during the load method, or deferred and called at a later time. Further loads going down will be blocked until the callback is called.

If data cannot be loaded (for example, if the request is invalid, or the data would be stale and inconsistent, it is valid to call invalidate() to invalidate the data source, and prevent further loading.

loadInitial

abstract fun loadInitial(
    @NonNull params: PageKeyedDataSource.LoadInitialParams<Key>, 
    @NonNull callback: PageKeyedDataSource.LoadInitialCallback<Key, Value>
): Unit

Load initial data.

This method is called first to initialize a PagedList with data. If it's possible to count the items that can be loaded by the DataSource, it's recommended to pass the loaded data to the callback via the three-parameter LoadInitialCallback#onResult(List, int, int, Object, Object). This enables PagedLists presenting data from this source to display placeholders to represent unloaded items.

LoadInitialParams#requestedLoadSize is a hint, not a requirement, so it may be may be altered or ignored.

map

@NonNull fun <ToValue : Any!> map(@NonNull function: Function<Value, ToValue>): PageKeyedDataSource<Key, ToValue>

mapByPage

@NonNull fun <ToValue : Any!> mapByPage(@NonNull function: Function<MutableList<Value>!, MutableList<ToValue>!>): PageKeyedDataSource<Key, ToValue>