PositionalDataSource

Artifact: androidx.paging:paging-common

View Source

Added in 2.0.0

Deprecated in 3.0.0

---

Kotlin |Java

Common/AllAndroid/JVMNative/C/iOSJavaScript

• android

  abstract class PositionalDataSource<T : Any> : DataSource

kotlin.Any
↳	androidx.paging.DataSource
	↳	androidx.paging.PositionalDataSource

---

This class is deprecated.
PositionalDataSource is deprecated and has been replaced by PagingSource

Position-based data loader for a fixed-size, countable data set, supporting fixed-size loads at arbitrary page positions.

Extend PositionalDataSource if you can load pages of a requested size at arbitrary positions, and provide a fixed item count. If your data source can't support loading arbitrary requested page sizes (e.g. when network page size constraints are only known at runtime), either use PageKeyedDataSource or ItemKeyedDataSource, or pass the initial result with the two parameter LoadInitialCallback.onResult.

Room can generate a Factory of PositionalDataSources for you:

@Dao
interface UserDao {
    @Query("SELECT * FROM user ORDER BY age DESC")
    public abstract DataSource.Factory<Integer, User> loadUsersByAgeDesc();
}

Parameters
<T : Any>	Type of items being loaded by the PositionalDataSource.

Summary

Nested types
abstract class PositionalDataSource.LoadInitialCallback<T : Any?> This class is deprecated. PositionalDataSource is deprecated and has been replaced by PagingSource
open class PositionalDataSource.LoadInitialParams This class is deprecated. PositionalDataSource is deprecated and has been replaced by PagingSource
abstract class PositionalDataSource.LoadRangeCallback<T : Any?> This class is deprecated. PositionalDataSource is deprecated and has been replaced by PagingSource
open class PositionalDataSource.LoadRangeParams This class is deprecated. PositionalDataSource is deprecated and has been replaced by PagingSource

Public companion functions
Int	computeInitialLoadPosition(     params: PositionalDataSource.LoadInitialParams,     totalCount: Int ) This function is deprecated. PositionalDataSource is deprecated and has been replaced by PagingSource	android
Int	computeInitialLoadSize(     params: PositionalDataSource.LoadInitialParams,     initialLoadPosition: Int,     totalCount: Int ) This function is deprecated. PositionalDataSource is deprecated and has been replaced by PagingSource	android

Public constructors
<T : Any> PositionalDataSource() This function is deprecated. PositionalDataSource is deprecated and has been replaced by PagingSource	android

Public functions
abstract Unit	@WorkerThread loadInitial(     params: PositionalDataSource.LoadInitialParams,     callback: PositionalDataSource.LoadInitialCallback<T> ) This function is deprecated. PositionalDataSource is deprecated and has been replaced by PagingSource	android
abstract Unit	@WorkerThread loadRange(     params: PositionalDataSource.LoadRangeParams,     callback: PositionalDataSource.LoadRangeCallback<T> ) This function is deprecated. PositionalDataSource is deprecated and has been replaced by PagingSource	android
final PositionalDataSource<V>	<V : Any> map(function: Function<T, V>) This function is deprecated. PositionalDataSource is deprecated and has been replaced by PagingSource	android
final PositionalDataSource<V>	<V : Any> map(function: (T) -> V) This function is deprecated. PositionalDataSource is deprecated and has been replaced by PagingSource	android
final PositionalDataSource<V>	<V : Any> mapByPage(function: Function<List<T>, List<V>>) This function is deprecated. PositionalDataSource is deprecated and has been replaced by PagingSource	android
final PositionalDataSource<V>	<V : Any> mapByPage(function: (List<T>) -> List<V>) This function is deprecated. PositionalDataSource is deprecated and has been replaced by PagingSource	android

Inherited functions

From androidx.paging.DataSource open Unit @AnyThread addInvalidatedCallback(     onInvalidatedCallback: DataSource.InvalidatedCallback ) This function is deprecated. PositionalDataSource is deprecated and has been replaced by PagingSource android open Unit @AnyThread invalidate() This function is deprecated. PositionalDataSource is deprecated and has been replaced by PagingSource android open Unit @AnyThread removeInvalidatedCallback(     onInvalidatedCallback: DataSource.InvalidatedCallback ) This function is deprecated. PositionalDataSource is deprecated and has been replaced by PagingSource android

Inherited properties
From androidx.paging.DataSource open Boolean isInvalid This property is deprecated. PositionalDataSource is deprecated and has been replaced by PagingSource android

Public companion functions

computeInitialLoadPosition

android

Added in 3.3.0

Deprecated in 3.3.0

fun computeInitialLoadPosition(
    params: PositionalDataSource.LoadInitialParams,
    totalCount: Int
): Int

This function is deprecated.
PositionalDataSource is deprecated and has been replaced by PagingSource

Helper for computing an initial position in loadInitial when total data set size can be computed ahead of loading.

The value computed by this function will do bounds checking, page alignment, and positioning based on initial load size requested.

Example usage in a PositionalDataSource subclass:

class ItemDataSource extends PositionalDataSource<Item> {
    private int computeCount() {
        // actual count code here
    }

    private List<Item> loadRangeInternal(int startPosition, int loadCount) {
        // actual load code here
    }

    @Override
    public void loadInitial(@NonNull LoadInitialParams params,
        @NonNull LoadInitialCallback<Item> callback) {
        int totalCount = computeCount();
        int position = computeInitialLoadPosition(params, totalCount);
        int loadSize = computeInitialLoadSize(params, position, totalCount);
        callback.onResult(loadRangeInternal(position, loadSize), position, totalCount);
    }

    @Override
    public void loadRange(@NonNull LoadRangeParams params,
        @NonNull LoadRangeCallback<Item> callback) {
        callback.onResult(loadRangeInternal(params.startPosition, params.loadSize));
    }
}

Parameters
params: PositionalDataSource.LoadInitialParams	Params passed to loadInitial, including page size, and requested start / loadSize.
totalCount: Int	Total size of the data set.

Returns
Int	Position to start loading at.

See also
computeInitialLoadSize

computeInitialLoadSize

android

Added in 3.3.0

Deprecated in 3.3.0

fun computeInitialLoadSize(
    params: PositionalDataSource.LoadInitialParams,
    initialLoadPosition: Int,
    totalCount: Int
): Int

This function is deprecated.
PositionalDataSource is deprecated and has been replaced by PagingSource

Helper for computing an initial load size in loadInitial when total data set size can be computed ahead of loading.

This function takes the requested load size, and bounds checks it against the value returned by computeInitialLoadPosition.

Example usage in a PositionalDataSource subclass:

class ItemDataSource extends PositionalDataSource<Item> {
    private int computeCount() {
        // actual count code here
    }

    private List<Item> loadRangeInternal(int startPosition, int loadCount) {
        // actual load code here
    }

    @Override
    public void loadInitial(@NonNull LoadInitialParams params,
        @NonNull LoadInitialCallback<Item> callback) {
        int totalCount = computeCount();
        int position = computeInitialLoadPosition(params, totalCount);
        int loadSize = computeInitialLoadSize(params, position, totalCount);
        callback.onResult(loadRangeInternal(position, loadSize), position, totalCount);
    }

    @Override
    public void loadRange(@NonNull LoadRangeParams params,
        @NonNull LoadRangeCallback<Item> callback) {
        callback.onResult(loadRangeInternal(params.startPosition, params.loadSize));
    }
}

Parameters
params: PositionalDataSource.LoadInitialParams	Params passed to loadInitial, including page size, and requested start / loadSize.
initialLoadPosition: Int	Value returned by computeInitialLoadPosition
totalCount: Int	Total size of the data set.

Returns
Int	Number of items to load.

See also
computeInitialLoadPosition

Public constructors

PositionalDataSource

android

<T : Any> PositionalDataSource()

This function is deprecated.
PositionalDataSource is deprecated and has been replaced by PagingSource

Parameters
<T : Any>	Type of items being loaded by the PositionalDataSource.

Public functions

loadInitial

android

Added in 2.0.0

Deprecated in 3.0.0

@WorkerThread
abstract fun loadInitial(
    params: PositionalDataSource.LoadInitialParams,
    callback: PositionalDataSource.LoadInitialCallback<T>
): Unit

This function is deprecated.
PositionalDataSource is deprecated and has been replaced by PagingSource

Load initial list data.

This method is called to load the initial page(s) from the DataSource.

LoadResult list must be a multiple of pageSize to enable efficient tiling.

Parameters
params: PositionalDataSource.LoadInitialParams	Parameters for initial load, including requested start position, load size, and page size.
callback: PositionalDataSource.LoadInitialCallback<T>	Callback that receives initial load data, including position and total data set size.

loadRange

android

Added in 2.0.0

Deprecated in 3.0.0

@WorkerThread
abstract fun loadRange(
    params: PositionalDataSource.LoadRangeParams,
    callback: PositionalDataSource.LoadRangeCallback<T>
): Unit

This function is deprecated.
PositionalDataSource is deprecated and has been replaced by PagingSource

Called to load a range of data from the DataSource.

This method is called to load additional pages from the DataSource after the LoadInitialCallback passed to dispatchLoadInitial has initialized a PagedList.

Unlike loadInitial, this method must return the number of items requested, at the position requested.

Parameters
params: PositionalDataSource.LoadRangeParams	Parameters for load, including start position and load size.
callback: PositionalDataSource.LoadRangeCallback<T>	Callback that receives loaded data.

map

android

Added in 2.0.0

Deprecated in 3.0.0

final fun <V : Any> map(function: Function<T, V>): PositionalDataSource<V>

This function is deprecated.
PositionalDataSource is deprecated and has been replaced by PagingSource

Applies the given function to each value emitted by the DataSource.

Same as mapByPage, but operates on individual items.

Parameters
function: Function<T, V>	Function that runs on each loaded item, returning items of a potentially new type.

Returns
PositionalDataSource<V>	A new DataSource, which transforms items using the given function.

See also
mapByPage
map
mapByPage

map

android

Added in 3.0.0

Deprecated in 3.0.0

final fun <V : Any> map(function: (T) -> V): PositionalDataSource<V>

This function is deprecated.
PositionalDataSource is deprecated and has been replaced by PagingSource

Applies the given function to each value emitted by the DataSource.

An overload of map that accepts a kotlin function type.

Same as mapByPage, but operates on individual items.

Parameters
function: (T) -> V	Function that runs on each loaded item, returning items of a potentially new type.

Returns
PositionalDataSource<V>	A new DataSource, which transforms items using the given function.

See also
mapByPage
map

mapByPage

android

Added in 2.0.0

Deprecated in 3.0.0

final fun <V : Any> mapByPage(function: Function<List<T>, List<V>>): PositionalDataSource<V>

This function is deprecated.
PositionalDataSource is deprecated and has been replaced by PagingSource

Applies the given function to each value emitted by the DataSource.

Same as map, but allows for batch conversions.

Parameters
function: Function<List<T>, List<V>>	Function that runs on each loaded page, returning items of a potentially new type.

Returns
PositionalDataSource<V>	A new DataSource, which transforms items using the given function.

See also
map
map
mapByPage

mapByPage

android

final fun <V : Any> mapByPage(function: (List<T>) -> List<V>): PositionalDataSource<V>

This function is deprecated.
PositionalDataSource is deprecated and has been replaced by PagingSource

Applies the given function to each value emitted by the DataSource.

An overload of mapByPage that accepts a kotlin function type.

Same as map, but allows for batch conversions.

Parameters
function: (List<T>) -> List<V>	Function that runs on each loaded page, returning items of a potentially new type.

Returns
PositionalDataSource<V>	A new DataSource, which transforms items using the given function.

See also
map
map
mapByPage