Should I subclass the NSMutableArray class

by

NSMutableArray is not a concrete class, it is just the abstract superclass of a class cluster. The documentation for NSMutableArray does have information about how to subclass, but also strongly advises you not to! Only subclass if you have a special need for actual storage.

A class cluster means that the actual class will be chosen at run-time. An array created empty, may not use the same class as an array created with 1000 items. The run-time can do smart choices of what implementation to use for you. In practice NSMutableArray will be a bridged CFArray. Nothing you need to worry about, but you might see it if you inspect the type of your arrays in the debugger, you will never see NSArray, but quite often NSCFArray.

As mentioned before, subclassing is not the same as extending a class. Objective-C has the concept of categories. A category is similar to what other programming languages call mix-ins.

If you for example want a convenience method on NSMutableArray to sort all members on a property, then define the category interface in a .h file as such:

@interface NSMutableArray (CWFirstnameSort)
-(void)sortObjectsByProperty:(NSString*)propertyName;
@end

And the implementation would be:

@implementation NSMutableArray (CWFirstnameSort)
-(void)sortObjectsByProperty:(NSString*)propertyName;
{
    NSSortDescriptor* sortDesc = [NSSortDescriptor sortDescriptorWithKey:propertName ascending:YES];
    [self sortUsingDescriptors:[NSArray arrayWithObject:sortDesc]];
}
@end

Then use it simply as:

[people sortObjectsByProperty:@"firstName"];

More Related Contents:

  1. Avoiding “NSArray was mutated while being enumerated”
  2. 2D arrays using NSMutableArray
  3. Removing duplicates from NSMutableArray
  4. How do I sort an NSMutableArray with custom objects in it?
  5. NSMutableArray addObject not working
  6. NSString property: copy or retain?
  7. Get the current first responder without using a private API
  8. Cannot add items to an NSMutableArray ivar
  9. How to print out the method name and line number and conditionally disable NSLog?
  10. Saving UIColor to and loading from NSUserDefaults
  11. Underscore prefix on property name? [duplicate]
  12. Converting a string to an NSDate
  13. How to use custom delegates in Objective-C
  14. Why shouldn’t I subclass a UIButton?
  15. Circular Progress Bars in IOS
  16. Xcode doesn’t show the line that causes a crash
  17. Is there a way to suppress warnings in Xcode?
  18. How can I get an NSDate object for today at midnight?
  19. How to pass object with NSNotificationCenter
  20. Fitting a UIDatePicker into a UIActionSheet
  21. With ARC, what’s better: alloc or autorelease initializers?
  22. Combining a UILongPressGestureRecognizer with a UIPanGestureRecognizer
  23. Easy way to dismiss keyboard?
  24. What is the BOOL *stop argument for enumerateObjectsUsingBlock: used for?
  25. Simple http post example in Objective-C?
  26. Animate infinite scrolling of an image in a seamless loop
  27. UITextField subview of UITableViewCell, get indexPath of cell
  28. iPhone – Differences among time zone convenience methods
  29. Class method equivalent of -respondsToSelector:
  30. Objective-C Difference between setting nil and releasing

Leave a Comment