PositionalDataSource
public
abstract
class
PositionalDataSource
extends DataSource<Integer, T>
java.lang.Object | ||
↳ | android.arch.paging.DataSource<java.lang.Integer, T> | |
↳ | android.arch.paging.PositionalDataSource<T> |
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), use
either PageKeyedDataSource
or ItemKeyedDataSource
instead.
Note that unless placeholders are disabled
PositionalDataSource requires counting the size of the data set. This allows pages to be tiled in
at arbitrary, non-contiguous locations based upon what the user observes in a PagedList
.
If placeholders are disabled, initialize with the two parameter
onResult(List, int)
.
Room can generate a Factory of PositionalDataSources for you:
@Dao interface UserDao { @Query("SELECT * FROM user ORDER BY mAge DESC") public abstract DataSource.Factory<Integer, User> loadUsersByAgeDesc(); }
Summary
Nested classes | |
---|---|
class |
PositionalDataSource.LoadInitialCallback<T>
Callback for |
class |
PositionalDataSource.LoadInitialParams
Holder object for inputs to |
class |
PositionalDataSource.LoadRangeCallback<T>
Callback for PositionalDataSource |
class |
PositionalDataSource.LoadRangeParams
Holder object for inputs to |
Public constructors | |
---|---|
PositionalDataSource()
|
Public methods | |
---|---|
static
int
|
computeInitialLoadPosition(PositionalDataSource.LoadInitialParams params, int totalCount)
Helper for computing an initial position in
|
static
int
|
computeInitialLoadSize(PositionalDataSource.LoadInitialParams params, int initialLoadPosition, int totalCount)
Helper for computing an initial load size in
|
abstract
void
|
loadInitial(PositionalDataSource.LoadInitialParams params, LoadInitialCallback<T> callback)
Load initial list data. |
abstract
void
|
loadRange(PositionalDataSource.LoadRangeParams params, LoadRangeCallback<T> callback)
Called to load a range of data from the DataSource. |
final
<V>
PositionalDataSource<V>
|
map(Function<T, V> function)
Applies the given function to each value emitted by the DataSource. |
final
<V>
PositionalDataSource<V>
|
mapByPage(Function<List<T>, List<V>> function)
Applies the given function to each value emitted by the DataSource. |
Inherited methods | |
---|---|
Public constructors
PositionalDataSource
PositionalDataSource ()
Public methods
computeInitialLoadPosition
int computeInitialLoadPosition (PositionalDataSource.LoadInitialParams params, int totalCount)
Helper for computing an initial position in
loadInitial(LoadInitialParams, LoadInitialCallback)
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(LoadInitialParams, LoadInitialCallback) ,
including page size, and requested start/loadSize. |
totalCount |
int : Total size of the data set. |
Returns | |
---|---|
int |
Position to start loading at. |
computeInitialLoadSize
int computeInitialLoadSize (PositionalDataSource.LoadInitialParams params, int initialLoadPosition, int totalCount)
Helper for computing an initial load size in
loadInitial(LoadInitialParams, LoadInitialCallback)
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(LoadInitialParams, int)
.
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(LoadInitialParams, LoadInitialCallback) ,
including page size, and requested start/loadSize. |
initialLoadPosition |
int : Value returned by
computeInitialLoadPosition(LoadInitialParams, int) |
totalCount |
int : Total size of the data set. |
Returns | |
---|---|
int |
Number of items to load. |
loadInitial
void loadInitial (PositionalDataSource.LoadInitialParams params, LoadInitialCallback<T> callback)
Load initial list data.
This method is called to load the initial page(s) from the DataSource.
Result 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 |
LoadInitialCallback : Callback that receives initial load data, including
position and total data set size.
|
loadRange
void loadRange (PositionalDataSource.LoadRangeParams params, LoadRangeCallback<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(LoadInitialParams, LoadInitialCallback)
, 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 |
LoadRangeCallback : Callback that receives loaded data.
|
map
PositionalDataSource<V> map (Function<T, V> function)
Applies the given function to each value emitted by the DataSource.
Same as mapByPage(Function)
, but operates on individual items.
Parameters | |
---|---|
function |
Function : 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. |
mapByPage
PositionalDataSource<V> mapByPage (Function<List<T>, List<V>> function)
Applies the given function to each value emitted by the DataSource.
Same as map(Function)
, but allows for batch conversions.
Parameters | |
---|---|
function |
Function : 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. |
Interfaces
Classes
- AsyncPagedListDiffer
- DataSource
- DataSource.Factory
- ItemKeyedDataSource
- ItemKeyedDataSource.LoadCallback
- ItemKeyedDataSource.LoadInitialCallback
- ItemKeyedDataSource.LoadInitialParams
- ItemKeyedDataSource.LoadParams
- LivePagedListBuilder
- PagedList
- PagedList.BoundaryCallback
- PagedList.Builder
- PagedList.Callback
- PagedList.Config
- PagedList.Config.Builder
- PagedListAdapter
- PageKeyedDataSource
- PageKeyedDataSource.LoadCallback
- PageKeyedDataSource.LoadInitialCallback
- PageKeyedDataSource.LoadInitialParams
- PageKeyedDataSource.LoadParams
- PositionalDataSource
- PositionalDataSource.LoadInitialCallback
- PositionalDataSource.LoadInitialParams
- PositionalDataSource.LoadRangeCallback
- PositionalDataSource.LoadRangeParams
- RxPagedListBuilder
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Last updated 2024-04-11 UTC.