Overview

The UILocalizedIndexedCollation class is a convenience for organizing, sorting, and localizing the data for a table view that has a section index. The table view‚Äôs data source then uses the collation object to provide the table view with input for section titles and section index titles.

Table views with section indexes are ideal for displaying and facilitating the access of data composed of many items organized by a sequential ordering scheme such as the alphabet. Users tap an index title to jump to the corresponding section. The initial table view of the Phone/Contacts application on the iPhone is an example. Note that the section titles can be different than the titles of the index.

To prepare the data for a section index, the UITableViewController object creates a indexed-collation object and then, for each model object that is to be indexed, calls sectionForObject:collationStringSelector:. This method determines the section in which each of these objects should appear and returns an integer that identifies the section. The table-view controller then puts each object in a local array for its section. For each section array, the controller calls the sortedArrayFromArray:collationStringSelector: method to sort all of the objects in the section. The indexed-collation object is now the data store that the table-view controller uses to provide section-index data to the table view, as illustrated in Listing 1.

Listing 1  Data source using indexed-collation object to provide data to table view

- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section

{

    return [[[UILocalizedIndexedCollation currentCollation] sectionTitles] objectAtIndex:section];

}

- (NSArray *)sectionIndexTitlesForTableView:(UITableView *)tableView

{

    return [[UILocalizedIndexedCollation currentCollation] sectionIndexTitles];

}

- (NSInteger)tableView:(UITableView *)tableView sectionForSectionIndexTitle:(NSString *)title atIndex:(NSInteger)index

{

    return [[UILocalizedIndexedCollation currentCollation] sectionForSectionIndexTitleAtIndex:index];

}