paging/rxjava2/src/main/java/androidx/paging/RxPagedListBuilder.kt - platform/frameworks/support - Git at Google

 /*
  * Copyright 2018 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 package androidx.paging

 import android.annotation.SuppressLint
 import androidx.arch.core.executor.ArchTaskExecutor
 import io.reactivex.BackpressureStrategy
 import io.reactivex.Flowable
 import io.reactivex.Observable
 import io.reactivex.ObservableEmitter
 import io.reactivex.ObservableOnSubscribe
 import io.reactivex.Scheduler
 import io.reactivex.functions.Cancellable
 import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.GlobalScope
 import kotlinx.coroutines.Job
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.rx2.SchedulerCoroutineDispatcher
 import kotlinx.coroutines.rx2.asCoroutineDispatcher
 import kotlinx.coroutines.withContext

 /**
  * Builder for `Observable<PagedList>` or `Flowable<PagedList>`, given a [DataSource.Factory] and a
  * [PagedList.Config].
  *
  * The required parameters are in the constructor, so you can simply construct and build, or
  * optionally enable extra features (such as initial load key, or BoundaryCallback).
  *
  * The returned observable/flowable will already be subscribed on the [setFetchScheduler], and will
  * perform all loading on that scheduler. It will already be observed on [setNotifyScheduler], and
  * will dispatch new PagedLists, as well as their updates to that scheduler.
  *
  * @param Key Type of input valued used to load data from the [DataSource]. Must be integer if
  * you're using [PositionalDataSource].
  * @param Value Item type being presented.
  *
  */
 class RxPagedListBuilder<Key : Any, Value : Any> {
     private val pagingSourceFactory: (() -> PagingSource<Key, Value>)?
     private val dataSourceFactory: DataSource.Factory<Key, Value>?
     @Suppress("DEPRECATION")
     private val config: PagedList.Config

     private var initialLoadKey: Key? = null
     @Suppress("DEPRECATION")
     private var boundaryCallback: PagedList.BoundaryCallback<Value>? = null
     private var notifyDispatcher: SchedulerCoroutineDispatcher? = null
     private var notifyScheduler: Scheduler? = null
     private var fetchDispatcher: SchedulerCoroutineDispatcher? = null
     private var fetchScheduler: Scheduler? = null

     /**
      * Creates a [RxPagedListBuilder] with required parameters.
      *
      * @param pagingSourceFactory DataSource factory providing DataSource generations.
      * @param config Paging configuration.
      */
     @Deprecated(
         message = "PagedList is deprecated and has been replaced by PagingData",
         replaceWith = ReplaceWith(
             """PagingDataFlowable(
                 config = PagingConfig(
                     config.pageSize,
                     config.prefetchDistance,
                     config.enablePlaceholders,
                     config.initialLoadSizeHint,
                     config.maxSize
                 ),
                 initialKey = null,
                 strategy = BackpressureStrategy.LATEST,
                 pagingSourceFactory = pagingSourceFactory
             )""",
             "androidx.paging.PagingConfig",
             "androidx.paging.PagingDataFlowable",
             "io.reactivex.BackpressureStrategy"
         )
     )
     constructor(
         pagingSourceFactory: () -> PagingSource<Key, Value>,
         @Suppress("DEPRECATION") config: PagedList.Config
     ) {
         this.pagingSourceFactory = pagingSourceFactory
         this.dataSourceFactory = null
         this.config = config
     }

     /**
      * Creates a [RxPagedListBuilder] with required parameters.
      *
      * This method is a convenience for:
      * ```
      * RxPagedListBuilder(
      *     pagingSourceFactory,
      *     PagedList.Config.Builder().setPageSize(pageSize).build()
      * )
      * ```
      *
      * @param pagingSourceFactory [PagingSource] factory providing [PagingSource] generations.
      * @param pageSize Size of pages to load.
      */
     @Suppress("DEPRECATION")
     @Deprecated(
         message = "PagedList is deprecated and has been replaced by PagingData",
         replaceWith = ReplaceWith(
             """PagingDataFlowable(
                 config = PagingConfig(pageSize),
                 initialKey = null,
                 strategy = BackpressureStrategy.LATEST,
                 pagingSourceFactory = pagingSourceFactory
             )""",
             "androidx.paging.PagingConfig",
             "androidx.paging.PagingDataFlowable",
             "io.reactivex.BackpressureStrategy"
         )
     )
     constructor(pagingSourceFactory: () -> PagingSource<Key, Value>, pageSize: Int) : this(
         pagingSourceFactory,
         PagedList.Config.Builder().setPageSize(pageSize).build()
     )

     /**
      * Creates a [RxPagedListBuilder] with required parameters.
      *
      * @param dataSourceFactory DataSource factory providing DataSource generations.
      * @param config Paging configuration.
      */
     @Deprecated(
         message = "PagedList is deprecated and has been replaced by PagingData",
         replaceWith = ReplaceWith(
             """PagingDataFlowable(
                 config = PagingConfig(
                     config.pageSize,
                     config.prefetchDistance,
                     config.enablePlaceholders,
                     config.initialLoadSizeHint,
                     config.maxSize
                 ),
                 initialKey = null,
                 strategy = BackpressureStrategy.LATEST,
                 this.asPagingSourceFactory(Dispatchers.IO)
             )""",
             "androidx.paging.PagingConfig",
             "androidx.paging.PagingDataFlowable",
             "io.reactivex.BackpressureStrategy",
             "kotlinx.coroutines.Dispatchers"
         )
     )
     constructor(
         dataSourceFactory: DataSource.Factory<Key, Value>,
         @Suppress("DEPRECATION") config: PagedList.Config
     ) {
         this.pagingSourceFactory = null
         this.dataSourceFactory = dataSourceFactory
         this.config = config
     }

     /**
      * Creates a [RxPagedListBuilder] with required parameters.
      *
      * This method is a convenience for:
      * ```
      * RxPagedListBuilder(
      *     dataSourceFactory,
      *     PagedList.Config.Builder().setPageSize(pageSize).build()
      * )
      * ```
      *
      * @param dataSourceFactory [DataSource.Factory] providing DataSource generations.
      * @param pageSize Size of pages to load.
      */
     @Suppress("DEPRECATION")
     @Deprecated(
         message = "PagedList is deprecated and has been replaced by PagingData",
         replaceWith = ReplaceWith(
             """PagingDataFlowable(
                 config = PagingConfig(pageSize),
                 initialKey = null,
                 strategy = BackpressureStrategy.LATEST,
                 this.asPagingSourceFactory(Dispatchers.IO)
             )""",
             "androidx.paging.PagingConfig",
             "androidx.paging.PagingDataFlowable",
             "io.reactivex.BackpressureStrategy",
             "kotlinx.coroutines.Dispatchers"
         )
     )
     constructor(
         dataSourceFactory: DataSource.Factory<Key, Value>,
         pageSize: Int
     ) : this(
         dataSourceFactory,
         PagedList.Config.Builder().setPageSize(pageSize).build()
     )

     /**
      * First loading key passed to the first PagedList/DataSource.
      *
      * When a new PagedList/DataSource pair is created after the first, it acquires a load key from
      * the previous generation so that data is loaded around the position already being observed.
      *
      * @param key Initial load key passed to the first PagedList/DataSource.
      * @return this
      */
     fun setInitialLoadKey(key: Key?) = apply {
         initialLoadKey = key
     }

     /**
      * Sets a [androidx.paging.PagedList.BoundaryCallback] on each PagedList created,
      * typically used to load additional data from network when paging from local storage.
      *
      * Pass a BoundaryCallback to listen to when the PagedList runs out of data to load. If this
      * method is not called, or `null` is passed, you will not be notified when each
      * DataSource runs out of data to provide to its PagedList.
      *
      * If you are paging from a DataSource.Factory backed by local storage, you can set a
      * BoundaryCallback to know when there is no more information to page from local storage.
      * This is useful to page from the network when local storage is a cache of network data.
      *
      * Note that when using a BoundaryCallback with a `Observable<PagedList>`, method calls
      * on the callback may be dispatched multiple times - one for each PagedList/DataSource
      * pair. If loading network data from a BoundaryCallback, you should prevent multiple
      * dispatches of the same method from triggering multiple simultaneous network loads.
      *
      * @param boundaryCallback The boundary callback for listening to PagedList load state.
      * @return this
      */
     fun setBoundaryCallback(
         @Suppress("DEPRECATION") boundaryCallback: PagedList.BoundaryCallback<Value>?
     ) = apply { this.boundaryCallback = boundaryCallback }

     /**
      * Sets scheduler which will be used for observing new PagedLists, as well as loading updates
      * within the PagedLists.
      *
      * If not set, defaults to the UI thread.
      *
      * The built [Observable] / [Flowable] will be observed on this scheduler, so that the thread
      * receiving PagedLists will also receive the internal updates to the PagedList.
      *
      * @param scheduler Scheduler that receives PagedList updates, and where [PagedList.Callback]
      * calls are dispatched. Generally, this is the UI/main thread.
      * @return this
      */
     fun setNotifyScheduler(scheduler: Scheduler) = apply {
         notifyScheduler = scheduler
         notifyDispatcher = scheduler.asCoroutineDispatcher()
     }

     /**
      * Sets scheduler which will be used for background fetching of PagedLists, as well as on-demand
      * fetching of pages inside.
      *
      * If not set, defaults to the Arch components I/O thread pool.
      *
      * The built [Observable] / [Flowable] will be subscribed on this scheduler.
      *
      * @param scheduler [Scheduler] used to fetch from DataSources, generally a background thread
      * pool for e.g. I/O or network loading.
      * @return this
      */
     fun setFetchScheduler(scheduler: Scheduler) = apply {
         fetchScheduler = scheduler
         fetchDispatcher = scheduler.asCoroutineDispatcher()
     }

     /**
      * Constructs a `Observable<PagedList>`.
      *
      * The returned Observable will already be observed on the [notifyScheduler], and subscribed on
      * the [fetchScheduler].
      *
      * @return The [Observable] of PagedLists
      */
     @Suppress("DEPRECATION")
     fun buildObservable(): Observable<PagedList<Value>> {
         @SuppressLint("RestrictedApi")
         val notifyScheduler = notifyScheduler
             ?: ScheduledExecutor(ArchTaskExecutor.getMainThreadExecutor())
         val notifyDispatcher = notifyDispatcher ?: notifyScheduler.asCoroutineDispatcher()

         @SuppressLint("RestrictedApi")
         val fetchScheduler = fetchScheduler
             ?: ScheduledExecutor(ArchTaskExecutor.getIOThreadExecutor())
         val fetchDispatcher = fetchDispatcher ?: fetchScheduler.asCoroutineDispatcher()

         val pagingSourceFactory = pagingSourceFactory
             ?: dataSourceFactory?.asPagingSourceFactory(fetchDispatcher)

         check(pagingSourceFactory != null) {
             "LivePagedList cannot be built without a PagingSourceFactory or DataSource.Factory"
         }

         return Observable
             .create(
                 PagingObservableOnSubscribe(
                     initialLoadKey,
                     config,
                     boundaryCallback,
                     pagingSourceFactory,
                     notifyDispatcher,
                     fetchDispatcher
                 )
             )
             .observeOn(notifyScheduler)
             .subscribeOn(fetchScheduler)
     }

     /**
      * Constructs a `Flowable<PagedList>`.
      *
      * The returned Observable will already be observed on the [notifyScheduler], and subscribed on
      * the [fetchScheduler].
      *
      * @param backpressureStrategy BackpressureStrategy for the [Flowable] to use.
      * @return The [Flowable] of PagedLists
      */
     @Suppress("DEPRECATION")
     fun buildFlowable(backpressureStrategy: BackpressureStrategy): Flowable<PagedList<Value>> {
         return buildObservable().toFlowable(backpressureStrategy)
     }

     @Suppress("DEPRECATION")
     internal class PagingObservableOnSubscribe<Key : Any, Value : Any>(
         initialLoadKey: Key?,
         private val config: PagedList.Config,
         private val boundaryCallback: PagedList.BoundaryCallback<Value>?,
         private val pagingSourceFactory: () -> PagingSource<Key, Value>,
         private val notifyDispatcher: CoroutineDispatcher,
         private val fetchDispatcher: CoroutineDispatcher
     ) : ObservableOnSubscribe<PagedList<Value>>, Cancellable {
         private var firstSubscribe = true
         private var currentData: PagedList<Value>
         private var currentJob: Job? = null
         private lateinit var emitter: ObservableEmitter<PagedList<Value>>

         private val callback = {
             invalidate(true)
         }

         private val refreshRetryCallback = Runnable { invalidate(true) }

         init {
             currentData = InitialPagedList(
                 pagingSourceFactory(),
                 GlobalScope,
                 config,
                 initialLoadKey
             )
             currentData.setRetryCallback(refreshRetryCallback)
         }

         override fun subscribe(emitter: ObservableEmitter<PagedList<Value>>) {
             this.emitter = emitter
             emitter.setCancellable(this)

             if (firstSubscribe) {
                 emitter.onNext(currentData)
                 firstSubscribe = false
             }

             invalidate(false)
         }

         override fun cancel() {
             currentData.pagingSource.unregisterInvalidatedCallback(callback)
         }

         private fun invalidate(force: Boolean) {
             // work is already ongoing, not forcing, so skip invalidate
             if (currentJob != null && !force) return

             currentJob?.cancel()
             currentJob = GlobalScope.launch(fetchDispatcher) {
                 currentData.pagingSource.unregisterInvalidatedCallback(callback)
                 val pagingSource = pagingSourceFactory()
                 pagingSource.registerInvalidatedCallback(callback)

                 withContext(notifyDispatcher) {
                     currentData.setInitialLoadState(LoadType.REFRESH, LoadState.Loading)
                 }

                 @Suppress("UNCHECKED_CAST")
                 val lastKey = currentData.lastKey as Key?
                 val params = config.toRefreshLoadParams(lastKey)
                 when (val initialResult = pagingSource.load(params)) {
                     is PagingSource.LoadResult.Error -> {
                         currentData.setInitialLoadState(
                             LoadType.REFRESH,
                             LoadState.Error(initialResult.throwable)
                         )
                     }
                     is PagingSource.LoadResult.Page -> {
                         val pagedList = PagedList.create(
                             pagingSource,
                             initialResult,
                             GlobalScope,
                             notifyDispatcher,
                             fetchDispatcher,
                             boundaryCallback,
                             config,
                             lastKey
                         )
                         onItemUpdate(currentData, pagedList)
                         currentData = pagedList
                         emitter.onNext(pagedList)
                     }
                 }
             }
         }

         private fun onItemUpdate(previous: PagedList<Value>, next: PagedList<Value>) {
             previous.setRetryCallback(null)
             next.setRetryCallback(refreshRetryCallback)
         }
     }
 }
	/*
	* Copyright 2018 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	package androidx.paging

	import android.annotation.SuppressLint
	import androidx.arch.core.executor.ArchTaskExecutor
	import io.reactivex.BackpressureStrategy
	import io.reactivex.Flowable
	import io.reactivex.Observable
	import io.reactivex.ObservableEmitter
	import io.reactivex.ObservableOnSubscribe
	import io.reactivex.Scheduler
	import io.reactivex.functions.Cancellable
	import kotlinx.coroutines.CoroutineDispatcher
	import kotlinx.coroutines.GlobalScope
	import kotlinx.coroutines.Job
	import kotlinx.coroutines.launch
	import kotlinx.coroutines.rx2.SchedulerCoroutineDispatcher
	import kotlinx.coroutines.rx2.asCoroutineDispatcher
	import kotlinx.coroutines.withContext

	/**
	* Builder for `Observable<PagedList>` or `Flowable<PagedList>`, given a [DataSource.Factory] and a
	* [PagedList.Config].
	*
	* The required parameters are in the constructor, so you can simply construct and build, or
	* optionally enable extra features (such as initial load key, or BoundaryCallback).
	*
	* The returned observable/flowable will already be subscribed on the [setFetchScheduler], and will
	* perform all loading on that scheduler. It will already be observed on [setNotifyScheduler], and
	* will dispatch new PagedLists, as well as their updates to that scheduler.
	*
	* @param Key Type of input valued used to load data from the [DataSource]. Must be integer if
	* you're using [PositionalDataSource].
	* @param Value Item type being presented.
	*
	*/
	class RxPagedListBuilder<Key : Any, Value : Any> {
	private val pagingSourceFactory: (() -> PagingSource<Key, Value>)?
	private val dataSourceFactory: DataSource.Factory<Key, Value>?
	@Suppress("DEPRECATION")
	private val config: PagedList.Config

	private var initialLoadKey: Key? = null
	@Suppress("DEPRECATION")
	private var boundaryCallback: PagedList.BoundaryCallback<Value>? = null
	private var notifyDispatcher: SchedulerCoroutineDispatcher? = null
	private var notifyScheduler: Scheduler? = null
	private var fetchDispatcher: SchedulerCoroutineDispatcher? = null
	private var fetchScheduler: Scheduler? = null

	/**
	* Creates a [RxPagedListBuilder] with required parameters.
	*
	* @param pagingSourceFactory DataSource factory providing DataSource generations.
	* @param config Paging configuration.
	*/
	@Deprecated(
	message = "PagedList is deprecated and has been replaced by PagingData",
	replaceWith = ReplaceWith(
	"""PagingDataFlowable(
	config = PagingConfig(
	config.pageSize,
	config.prefetchDistance,
	config.enablePlaceholders,
	config.initialLoadSizeHint,
	config.maxSize
	),
	initialKey = null,
	strategy = BackpressureStrategy.LATEST,
	pagingSourceFactory = pagingSourceFactory
	)""",
	"androidx.paging.PagingConfig",
	"androidx.paging.PagingDataFlowable",
	"io.reactivex.BackpressureStrategy"
	)
	)
	constructor(
	pagingSourceFactory: () -> PagingSource<Key, Value>,
	@Suppress("DEPRECATION") config: PagedList.Config
	) {
	this.pagingSourceFactory = pagingSourceFactory
	this.dataSourceFactory = null
	this.config = config
	}

	/**
	* Creates a [RxPagedListBuilder] with required parameters.
	*
	* This method is a convenience for:
	* ```
	* RxPagedListBuilder(
	* pagingSourceFactory,
	* PagedList.Config.Builder().setPageSize(pageSize).build()
	* )
	* ```
	*
	* @param pagingSourceFactory [PagingSource] factory providing [PagingSource] generations.
	* @param pageSize Size of pages to load.
	*/
	@Suppress("DEPRECATION")
	@Deprecated(
	message = "PagedList is deprecated and has been replaced by PagingData",
	replaceWith = ReplaceWith(
	"""PagingDataFlowable(
	config = PagingConfig(pageSize),
	initialKey = null,
	strategy = BackpressureStrategy.LATEST,
	pagingSourceFactory = pagingSourceFactory
	)""",
	"androidx.paging.PagingConfig",
	"androidx.paging.PagingDataFlowable",
	"io.reactivex.BackpressureStrategy"
	)
	)
	constructor(pagingSourceFactory: () -> PagingSource<Key, Value>, pageSize: Int) : this(
	pagingSourceFactory,
	PagedList.Config.Builder().setPageSize(pageSize).build()
	)

	/**
	* Creates a [RxPagedListBuilder] with required parameters.
	*
	* @param dataSourceFactory DataSource factory providing DataSource generations.
	* @param config Paging configuration.
	*/
	@Deprecated(
	message = "PagedList is deprecated and has been replaced by PagingData",
	replaceWith = ReplaceWith(
	"""PagingDataFlowable(
	config = PagingConfig(
	config.pageSize,
	config.prefetchDistance,
	config.enablePlaceholders,
	config.initialLoadSizeHint,
	config.maxSize
	),
	initialKey = null,
	strategy = BackpressureStrategy.LATEST,
	this.asPagingSourceFactory(Dispatchers.IO)
	)""",
	"androidx.paging.PagingConfig",
	"androidx.paging.PagingDataFlowable",
	"io.reactivex.BackpressureStrategy",
	"kotlinx.coroutines.Dispatchers"
	)
	)
	constructor(
	dataSourceFactory: DataSource.Factory<Key, Value>,
	@Suppress("DEPRECATION") config: PagedList.Config
	) {
	this.pagingSourceFactory = null
	this.dataSourceFactory = dataSourceFactory
	this.config = config
	}

	/**
	* Creates a [RxPagedListBuilder] with required parameters.
	*
	* This method is a convenience for:
	* ```
	* RxPagedListBuilder(
	* dataSourceFactory,
	* PagedList.Config.Builder().setPageSize(pageSize).build()
	* )
	* ```
	*
	* @param dataSourceFactory [DataSource.Factory] providing DataSource generations.
	* @param pageSize Size of pages to load.
	*/
	@Suppress("DEPRECATION")
	@Deprecated(
	message = "PagedList is deprecated and has been replaced by PagingData",
	replaceWith = ReplaceWith(
	"""PagingDataFlowable(
	config = PagingConfig(pageSize),
	initialKey = null,
	strategy = BackpressureStrategy.LATEST,
	this.asPagingSourceFactory(Dispatchers.IO)
	)""",
	"androidx.paging.PagingConfig",
	"androidx.paging.PagingDataFlowable",
	"io.reactivex.BackpressureStrategy",
	"kotlinx.coroutines.Dispatchers"
	)
	)
	constructor(
	dataSourceFactory: DataSource.Factory<Key, Value>,
	pageSize: Int
	) : this(
	dataSourceFactory,
	PagedList.Config.Builder().setPageSize(pageSize).build()
	)

	/**
	* First loading key passed to the first PagedList/DataSource.
	*
	* When a new PagedList/DataSource pair is created after the first, it acquires a load key from
	* the previous generation so that data is loaded around the position already being observed.
	*
	* @param key Initial load key passed to the first PagedList/DataSource.
	* @return this
	*/
	fun setInitialLoadKey(key: Key?) = apply {
	initialLoadKey = key
	}

	/**
	* Sets a [androidx.paging.PagedList.BoundaryCallback] on each PagedList created,
	* typically used to load additional data from network when paging from local storage.
	*
	* Pass a BoundaryCallback to listen to when the PagedList runs out of data to load. If this
	* method is not called, or `null` is passed, you will not be notified when each
	* DataSource runs out of data to provide to its PagedList.
	*
	* If you are paging from a DataSource.Factory backed by local storage, you can set a
	* BoundaryCallback to know when there is no more information to page from local storage.
	* This is useful to page from the network when local storage is a cache of network data.
	*
	* Note that when using a BoundaryCallback with a `Observable<PagedList>`, method calls
	* on the callback may be dispatched multiple times - one for each PagedList/DataSource
	* pair. If loading network data from a BoundaryCallback, you should prevent multiple
	* dispatches of the same method from triggering multiple simultaneous network loads.
	*
	* @param boundaryCallback The boundary callback for listening to PagedList load state.
	* @return this
	*/
	fun setBoundaryCallback(
	@Suppress("DEPRECATION") boundaryCallback: PagedList.BoundaryCallback<Value>?
	) = apply { this.boundaryCallback = boundaryCallback }

	/**
	* Sets scheduler which will be used for observing new PagedLists, as well as loading updates
	* within the PagedLists.
	*
	* If not set, defaults to the UI thread.
	*
	* The built [Observable] / [Flowable] will be observed on this scheduler, so that the thread
	* receiving PagedLists will also receive the internal updates to the PagedList.
	*
	* @param scheduler Scheduler that receives PagedList updates, and where [PagedList.Callback]
	* calls are dispatched. Generally, this is the UI/main thread.
	* @return this
	*/
	fun setNotifyScheduler(scheduler: Scheduler) = apply {
	notifyScheduler = scheduler
	notifyDispatcher = scheduler.asCoroutineDispatcher()
	}

	/**
	* Sets scheduler which will be used for background fetching of PagedLists, as well as on-demand
	* fetching of pages inside.
	*
	* If not set, defaults to the Arch components I/O thread pool.
	*
	* The built [Observable] / [Flowable] will be subscribed on this scheduler.
	*
	* @param scheduler [Scheduler] used to fetch from DataSources, generally a background thread
	* pool for e.g. I/O or network loading.
	* @return this
	*/
	fun setFetchScheduler(scheduler: Scheduler) = apply {
	fetchScheduler = scheduler
	fetchDispatcher = scheduler.asCoroutineDispatcher()
	}

	/**
	* Constructs a `Observable<PagedList>`.
	*
	* The returned Observable will already be observed on the [notifyScheduler], and subscribed on
	* the [fetchScheduler].
	*
	* @return The [Observable] of PagedLists
	*/
	@Suppress("DEPRECATION")
	fun buildObservable(): Observable<PagedList<Value>> {
	@SuppressLint("RestrictedApi")
	val notifyScheduler = notifyScheduler
	?: ScheduledExecutor(ArchTaskExecutor.getMainThreadExecutor())
	val notifyDispatcher = notifyDispatcher ?: notifyScheduler.asCoroutineDispatcher()

	@SuppressLint("RestrictedApi")
	val fetchScheduler = fetchScheduler
	?: ScheduledExecutor(ArchTaskExecutor.getIOThreadExecutor())
	val fetchDispatcher = fetchDispatcher ?: fetchScheduler.asCoroutineDispatcher()

	val pagingSourceFactory = pagingSourceFactory
	?: dataSourceFactory?.asPagingSourceFactory(fetchDispatcher)

	check(pagingSourceFactory != null) {
	"LivePagedList cannot be built without a PagingSourceFactory or DataSource.Factory"
	}

	return Observable
	.create(
	PagingObservableOnSubscribe(
	initialLoadKey,
	config,
	boundaryCallback,
	pagingSourceFactory,
	notifyDispatcher,
	fetchDispatcher
	)
	)
	.observeOn(notifyScheduler)
	.subscribeOn(fetchScheduler)
	}

	/**
	* Constructs a `Flowable<PagedList>`.
	*
	* The returned Observable will already be observed on the [notifyScheduler], and subscribed on
	* the [fetchScheduler].
	*
	* @param backpressureStrategy BackpressureStrategy for the [Flowable] to use.
	* @return The [Flowable] of PagedLists
	*/
	@Suppress("DEPRECATION")
	fun buildFlowable(backpressureStrategy: BackpressureStrategy): Flowable<PagedList<Value>> {
	return buildObservable().toFlowable(backpressureStrategy)
	}

	@Suppress("DEPRECATION")
	internal class PagingObservableOnSubscribe<Key : Any, Value : Any>(
	initialLoadKey: Key?,
	private val config: PagedList.Config,
	private val boundaryCallback: PagedList.BoundaryCallback<Value>?,
	private val pagingSourceFactory: () -> PagingSource<Key, Value>,
	private val notifyDispatcher: CoroutineDispatcher,
	private val fetchDispatcher: CoroutineDispatcher
	) : ObservableOnSubscribe<PagedList<Value>>, Cancellable {
	private var firstSubscribe = true
	private var currentData: PagedList<Value>
	private var currentJob: Job? = null
	private lateinit var emitter: ObservableEmitter<PagedList<Value>>

	private val callback = {
	invalidate(true)
	}

	private val refreshRetryCallback = Runnable { invalidate(true) }

	init {
	currentData = InitialPagedList(
	pagingSourceFactory(),
	GlobalScope,
	config,
	initialLoadKey
	)
	currentData.setRetryCallback(refreshRetryCallback)
	}

	override fun subscribe(emitter: ObservableEmitter<PagedList<Value>>) {
	this.emitter = emitter
	emitter.setCancellable(this)

	if (firstSubscribe) {
	emitter.onNext(currentData)
	firstSubscribe = false
	}

	invalidate(false)
	}

	override fun cancel() {
	currentData.pagingSource.unregisterInvalidatedCallback(callback)
	}

	private fun invalidate(force: Boolean) {
	// work is already ongoing, not forcing, so skip invalidate
	if (currentJob != null && !force) return

	currentJob?.cancel()
	currentJob = GlobalScope.launch(fetchDispatcher) {
	currentData.pagingSource.unregisterInvalidatedCallback(callback)
	val pagingSource = pagingSourceFactory()
	pagingSource.registerInvalidatedCallback(callback)

	withContext(notifyDispatcher) {
	currentData.setInitialLoadState(LoadType.REFRESH, LoadState.Loading)
	}

	@Suppress("UNCHECKED_CAST")
	val lastKey = currentData.lastKey as Key?
	val params = config.toRefreshLoadParams(lastKey)
	when (val initialResult = pagingSource.load(params)) {
	is PagingSource.LoadResult.Error -> {
	currentData.setInitialLoadState(
	LoadType.REFRESH,
	LoadState.Error(initialResult.throwable)
	)
	}
	is PagingSource.LoadResult.Page -> {
	val pagedList = PagedList.create(
	pagingSource,
	initialResult,
	GlobalScope,
	notifyDispatcher,
	fetchDispatcher,
	boundaryCallback,
	config,
	lastKey
	)
	onItemUpdate(currentData, pagedList)
	currentData = pagedList
	emitter.onNext(pagedList)
	}
	}
	}
	}

	private fun onItemUpdate(previous: PagedList<Value>, next: PagedList<Value>) {
	previous.setRetryCallback(null)
	next.setRetryCallback(refreshRetryCallback)
	}
	}
	}