Protocol

UITableViewDataSourcePrefetching

A protocol that provides advance warning of the data requirements for a table view, allowing the triggers of asynchronous data load operations.

Overview

You use a prefetch data source object in conjunction with your table view’s data source to begin loading data for cells before the tableView(_:cellForRowAt:) data source method is called.The following steps are required to add a prefetch data source to your table view:

When configuring the table view object, assign your prefetch data source to its prefetchDataSource property. For more information about how a table view works, see UITableView.

Loading Data Asynchronously

The tableView(_:prefetchRowsAt:) method is not necessarily called for every cell in the table view. Your implementation of tableView(_:cellForRowAt:) must therefore be able to cope with the following potential situations:

  • Data has been loaded via the prefetch request, and is ready to be displayed.

  • Data is currently being prefetched, but is not yet available.

  • Data has not yet been requested.

One approach that handles all of these situations is to use Operation to load the data for each row. You create the Operation object and store it in the prefetch method. The data source method can then either retrieve the operation and the result, or create it if it doesn’t exist. For further information about how you can use asynchronous programming models to achieve this desired behavior, see Concurrency Programming Guide.

Topics

Managing Data Prefetching

func tableView(UITableView, prefetchRowsAt: [IndexPath])

Instructs your prefetch data source object to begin preparing data for the cells at the supplied index paths.

Required.

func tableView(UITableView, cancelPrefetchingForRowsAt: [IndexPath])

Cancels a previously triggered data prefetch request.

Relationships

Inherits From

See Also

Providing the Table View Data

var dataSource: UITableViewDataSource?

The object that acts as the data source of the table view.

protocol UITableViewDataSource

The UITableViewDataSource protocol is adopted by an object that mediates the application’™s data model for a UITableView object. The data source provides the table-view object with the information it needs to construct and modify a table view.