{% setvar book_path %}/reference/androidx/_book.yaml{% endsetvar %} {% include "_shared/_reference-head-tags.html" %}
public abstract class PageKeyedDataSource.LoadInitialCallback<Key extends Object, Value extends Object>
Callback for loadInitial
to return data and, optionally, position/count information.
A callback can be called only once, and will throw if called again.
If you can compute the number of items in the data set before and after the loaded range, call the five parameter onResult
to pass that information. You can skip passing this information by calling the three parameter onResult
, either if it's difficult to compute, or if LoadInitialParams.placeholdersEnabled
is false
, so the positioning information will be ignored.
It is always valid for a DataSource loading method that takes a callback to stash the callback and call it later. This enables DataSources to be fully asynchronous, and to handle temporary, recoverable error states (such as a network error that can be retried).
Parameters | |
---|---|
<Key extends Object> |
Type of data used to query pages. |
<Value extends Object> |
Type of items being loaded. |
Public constructors |
|
---|---|
<Key extends Object, Value extends Object> LoadInitialCallback() |
Public methods |
|
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abstract void |
onResult( Called to pass initial load state from a DataSource. |
abstract void |
onResult( Called to pass loaded data from a DataSource. |
@NonNull
public final <Key extends Object, Value extends Object> LoadInitialCallback()
@NonNull
public abstract void onResult(
@NonNull List<@NonNull Value> data,
int position,
int totalCount,
@Nullable Key previousPageKey,
@Nullable Key nextPageKey
)
Called to pass initial load state from a DataSource.
Call this method from your DataSource's loadInitial
function to return data, and inform how many placeholders should be shown before and after. If counting is cheap to compute (for example, if a network load returns the information regardless), it's recommended to pass data back through this method.
It is always valid to pass a different amount of data than what is requested. Pass an empty list if there is no more data to load.
Parameters | |
---|---|
@NonNull List<@NonNull Value> data |
List of items loaded from the |
int position |
Position of the item at the front of the list. If there are |
int totalCount |
Total number of items that may be returned from this DataSource. Includes the number in the initial |
@NonNull
public abstract void onResult(
@NonNull List<@NonNull Value> data,
@Nullable Key previousPageKey,
@Nullable Key nextPageKey
)
Called to pass loaded data from a DataSource.
Call this from loadInitial
to initialize without counting available data, or supporting placeholders.
It is always valid to pass a different amount of data than what is requested. Pass an empty list if there is no more data to load.
Parameters | |
---|---|
@NonNull List<@NonNull Value> data |
List of items loaded from the |
@Nullable Key previousPageKey |
Key for page before the initial load result, or |
@Nullable Key nextPageKey |
Key for page after the initial load result, or |