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PositionalDataSource

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public abstract class PositionalDataSource<T extends Object> extends DataSource

Object
   ↳ DataSource
     ↳ PositionalDataSource

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 extends Object>

Type of items being loaded by the PositionalDataSource.

Summary

Nested types

PositionalDataSource.LoadInitialCallback

Callback for loadInitial to return data, position, and count.

PositionalDataSource.LoadInitialParams

Holder object for inputs to loadInitial.

PositionalDataSource.LoadRangeCallback

Callback for PositionalDataSource loadRange to return data.

PositionalDataSource.LoadRangeParams

Holder object for inputs to loadRange.

Public fields

boolean

Public constructors

Public methods

abstract @<ERROR CLASS> void

Load initial list data.

abstract @<ERROR CLASS> void

Called to load a range of data from the DataSource.

final @NonNull PositionalDataSource<@NonNull V>
<V extends Object> map(@NonNull <ERROR CLASS><@NonNull T, @NonNull V> function)

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

final @NonNull PositionalDataSource<@NonNull V>
<V extends Object> map(@NonNull Function1<@NonNull T, @NonNull V> function)

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

final @NonNull PositionalDataSource<@NonNull V>
<V extends Object> mapByPage(
    @NonNull <ERROR CLASS><@NonNull List<@NonNull T>, @NonNull List<@NonNull V>> function
)

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

final @NonNull PositionalDataSource<@NonNull V>
<V extends Object> mapByPage(
    @NonNull Function1<@NonNull List<@NonNull T>, @NonNull List<@NonNull V>> function
)

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

Inherited methods

From class DataSource
@<ERROR CLASS> void

Add a callback to invoke when the DataSource is first invalidated.

@<ERROR CLASS> void

Signal the data source to stop loading, and notify its callback.

@<ERROR CLASS> void

Remove a previously added invalidate callback.

Public fields

isInvalid

@NonNull
public boolean isInvalid
Returns
boolean

true if the data source is invalid, and can no longer be queried for data.

Public constructors

PositionalDataSource

@NonNull
public final <T extends Object> PositionalDataSource()
Parameters
<T extends Object>

Type of items being loaded by the PositionalDataSource.

Public methods

loadInitial

@<ERROR CLASS>
@NonNull
public abstract @<ERROR CLASS> void loadInitial(
    @NonNull PositionalDataSource.LoadInitialParams params,
    @NonNull PositionalDataSource.LoadInitialCallback<@NonNull T> callback
)

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
@NonNull PositionalDataSource.LoadInitialParams params

Parameters for initial load, including requested start position, load size, and page size.

@NonNull PositionalDataSource.LoadInitialCallback<@NonNull T> callback

Callback that receives initial load data, including position and total data set size.

loadRange

@<ERROR CLASS>
@NonNull
public abstract @<ERROR CLASS> void loadRange(
    @NonNull PositionalDataSource.LoadRangeParams params,
    @NonNull PositionalDataSource.LoadRangeCallback<@NonNull T> callback
)

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
@NonNull PositionalDataSource.LoadRangeParams params

Parameters for load, including start position and load size.

@NonNull PositionalDataSource.LoadRangeCallback<@NonNull T> callback

Callback that receives loaded data.

map

@NonNull
public final PositionalDataSource<@NonNull V> <V extends Object> map(@NonNull <ERROR CLASS><@NonNull T, @NonNull V> function)

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

Same as mapByPage, but operates on individual items.

Parameters
@NonNull <ERROR CLASS><@NonNull T, @NonNull V> function

Function that runs on each loaded item, returning items of a potentially new type.

Returns
PositionalDataSource<@NonNull V>

A new DataSource, which transforms items using the given function.

See also
mapByPage
map
mapByPage

map

@NonNull
public final PositionalDataSource<@NonNull V> <V extends Object> map(@NonNull Function1<@NonNull T, @NonNull V> function)

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

Same as mapByPage, but operates on individual items.

Parameters
@NonNull Function1<@NonNull T, @NonNull V> function

Function that runs on each loaded item, returning items of a potentially new type.

Returns
PositionalDataSource<@NonNull V>

A new DataSource, which transforms items using the given function.

See also
mapByPage
map
mapByPage

mapByPage

@NonNull
public final PositionalDataSource<@NonNull V> <V extends Object> mapByPage(
    @NonNull <ERROR CLASS><@NonNull List<@NonNull T>, @NonNull List<@NonNull V>> function
)

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

Same as map, but allows for batch conversions.

Parameters
@NonNull <ERROR CLASS><@NonNull List<@NonNull T>, @NonNull List<@NonNull V>> function

Function that runs on each loaded page, returning items of a potentially new type.

Returns
PositionalDataSource<@NonNull V>

A new DataSource, which transforms items using the given function.

See also
map
map
mapByPage

mapByPage

@NonNull
public final PositionalDataSource<@NonNull V> <V extends Object> mapByPage(
    @NonNull Function1<@NonNull List<@NonNull T>, @NonNull List<@NonNull V>> function
)

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

Same as map, but allows for batch conversions.

Parameters
@NonNull Function1<@NonNull List<@NonNull T>, @NonNull List<@NonNull V>> function

Function that runs on each loaded page, returning items of a potentially new type.

Returns
PositionalDataSource<@NonNull V>

A new DataSource, which transforms items using the given function.

See also
map
map
mapByPage