PositionalDataSource.LoadInitialCallback

public abstract class PositionalDataSource.LoadInitialCallback<T extends @Nullable Object>

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

A callback should be called only once, and may throw if called again.

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
<T extends @Nullable Object>

Type of items being loaded.

Summary

Public constructors

Public methods
abstract @NonNull void
onResult(
    @NonNull List<@NonNull T> data,
    @NonNull int position,
    @NonNull int totalCount
)

Called to pass initial load state from a DataSource.
abstract @NonNull void
onResult(@NonNull List<@NonNull T> data, @NonNull int position)

Called to pass initial load state from a DataSource without total count, when placeholders aren't requested.

Public constructors

LoadInitialCallback

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

Type of items being loaded.

Public methods

onResult

@NonNull
public abstract @NonNull void onResult(
    @NonNull List<@NonNull T> data,
    @NonNull int position,
    @NonNull int totalCount
)

Called to pass initial load state from a DataSource.

Call this method from loadInitial function to return data, and inform how many placeholders should be shown before and after. If counting is cheap compute (for example, if a network load returns the information regardless), it's recommended to pass the total size to the totalCount parameter. If placeholders are not requested (when LoadInitialParams.placeholdersEnabled is false), you can instead call onResult.

Parameters
@NonNull List<@NonNull T> data

List of items loaded from the DataSource. If this is empty, the DataSource is treated as empty, and no further loads will occur.
@NonNull int position

Position of the item at the front of the list. If there are N items before the items in data that can be loaded from this DataSource, pass N.
@NonNull int totalCount

Total number of items that may be returned from this DataSource. Includes the number in the initial data parameter as well as any items that can be loaded in front or behind of data.

onResult

@NonNull
public abstract @NonNull void onResult(@NonNull List<@NonNull T> data, @NonNull int position)

Called to pass initial load state from a DataSource without total count, when placeholders aren't requested.

Note: This method can only be called when placeholders are disabled (i.e., LoadInitialParams.placeholdersEnabled is false).

Call this method from loadInitial function to return data, if position is known but total size is not. If placeholders are requested, call the three parameter variant: onResult.

Parameters
@NonNull List<@NonNull T> data

List of items loaded from the DataSource. If this is empty, the DataSource is treated as empty, and no further loads will occur.
@NonNull int position

Position of the item at the front of the list. If there are N items before the items in data that can be provided by this DataSource, pass N.