NSComboBox controls rely on data source objects to provide the contents of the combo box. This informal protocol provides the interface for NSComboBoxCell data source objects to implement. It declares methods that not only provide the contents of the combo box list, but support autocompletion behavior (where a string is returned from the data source that matches a partially completed string typed into the combo box field). At a minimum, data source objects must implement the methods comboBoxCell:objectValueForItemAtIndex: and numberOfItemsInComboBoxCell:.

@interface NSObject (NSComboBoxCellDataSource)
// Instance Methods
- (int)numberOfItemsInComboBoxCell:(NSComboBoxCell *)comboBoxCell;
- (id)comboBoxCell:(NSComboBoxCell *)aComboBoxCell objectValueForItemAtIndex:(int)index;
- (unsigned int)comboBoxCell:(NSComboBoxCell *)aComboBoxCell indexOfItemWithStringValue:(NSString *)string;
- (NSString *)comboBoxCell:(NSComboBoxCell *)aComboBoxCell completedString:(NSString *)uncompletedString;
@end