A protocol that provides advance warning of the data requirements for a table view, allowing you to start potentially long-running data operations early.
- iOS 10.0+
- Mac Catalyst 13.0+
- tvOS 10.0+
You use a prefetch data source object in conjunction with your table view’s data source to begin loading data for cells before the
table data source method is called. The following steps are required to support a prefetch data source to your table view:
Create the table view and its regular data source.
Initiate asynchronous loading of the data required for the cells at the specified index paths in your implementation of
View: prefetch Rows At Index Paths:
Prepare the cell for display using the prefetched data in your
tabledata source method.
View: cell For Row At Index Path:
Cancel pending data load operations when the table view informs you that the data is no longer required in the
View: cancel Prefetching For Rows At Index Paths:
Loading Data Asynchronously
table method is not necessarily called for every cell in the table view. Your implementation of
table 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
NSOperation to load the data for each row. You create the
NSOperation 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.