範例1：

I think this will do it:

brandDescriptor = [[NSSortDescriptor alloc] initWithKey:@"brand" ascending:YES];
sortDescriptors = [NSArray arrayWithObject:brandDescriptor];
sortedArray = [myArray sortedArrayUsingDescriptors:sortDescriptors];

I pulled the code from Sort Descriptor Programming Topics. Also, Key-Value Coding comes into play, in that sortedArrayUsingDescriptors: will send a valueForKey: to each element in myArray, and then use standard comparators to sort the returned values.

 

範例2：

---

Compare method

Either you implement a compare-method for your object:

- (NSComparisonResult)compare:(Person *)otherObject {
    return [self.birthDate compare:otherObject.birthDate];
}

NSArray *sortedArray = [drinkDetails sortedArrayUsingSelector:@selector(compare:)];

NSSortDescriptor (better)

or usually even better:

NSSortDescriptor *sortDescriptor;
sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"birthDate"
                                              ascending:YES];
NSArray *sortDescriptors = [NSArray arrayWithObject:sortDescriptor];
NSArray *sortedArray = [drinkDetails sortedArrayUsingDescriptors:sortDescriptors];

You can easily sort by multiple keys by adding more than one to the array. Using custom comparator-methods is possible as well. Have a look at the documentation.

Blocks (shiny!)

There’s also the possibility of sorting with a block since Mac OS X 10.6 and iOS 4:

NSArray *sortedArray;
sortedArray = [drinkDetails sortedArrayUsingComparator:^NSComparisonResult(id a, id b) {
    NSDate *first = [(Person*)a birthDate];
    NSDate *second = [(Person*)b birthDate];
    return [first compare:second];
}];

Performance

The -compare: and block-based methods will be quite a bit faster, in general, than using NSSortDescriptor as the latter relies on KVC. The primary advantage of the NSSortDescriptormethod is that it provides a way to define your sort order using data, rather than code, which makes it easy to e.g. set things up so users can sort an NSTableView by clicking on the header row.

 

from:
http://stackoverflow.com/questions/805547/how-to-sort-an-nsmutablearray-with-custom-objects-in-it