{% setvar book_path %}/reference/kotlin/androidx/_book.yaml{% endsetvar %} {% include "_shared/_reference-head-tags.html" %}
abstract class ItemKeyedDataSource.LoadInitialCallback<Value : Any?> : ItemKeyedDataSource.LoadCallback
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 three parameter onResult
to pass that information. You can skip passing this information by calling the single 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 | |
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<Value : Any?> |
Type of items being loaded. |
Public constructors |
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<Value : Any?> LoadInitialCallback() |
Public functions |
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abstract Unit |
Called to pass initial load state from a DataSource. |
Inherited functions |
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<Value : Any?> LoadInitialCallback()
Parameters | |
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<Value : Any?> |
Type of items being loaded. |
abstract fun onResult(data: List<Value>, position: Int, totalCount: Int): Unit
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 | |
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data: List<Value> |
List of items loaded from the DataSource. If this is empty, the DataSource is treated as empty, and no further loads will occur. |
position: Int |
Position of the item at the front of the list. If there are |
totalCount: Int |
Total number of items that may be returned from this |