Return multiple objects from a method in Objective-C

Question

I have a method that takes an NSMutableArray as a parameter, and I would like it to return that array, another array that is created in the method, and an int created by the method. I realize this could be done by making an array that had all these objects in it, and returning that, then removing them from the array outside the method, but is there another way to return multiple objects?

Answer 1

Another way you can do it is have the user pass a pointer which they want to use to hold the data. Here is a sample that returns an array and uses pointers to give you an int value and another array. EDIT ok here is the working version I just tested it myself:

- (NSMutableArray*)doStuff:(int*)container returnedArray:(NSMutableArray*)arrayContainer{
   int a = 4;
   *container = a;
   [arrayContainer removeAllObjects];
   [arrayContainer addObject:@"object"];
   return [NSMutableArray arrayWithObjects:@"object",nil];
}

That way you could say like:

int value = 0;
NSMutableArray* new = [NSMutableArray array];
[self doStuff:&value returnedArray:new];

And it basicly works like a return!

Answer 2

Using an NSDictionary to return multiple values is the customary way to do this in Obj-C.

The method signature would look something like this:

-(NSDictionary *)doSomeStuffThatReturnsMultipleObjects;

and you are going to want to define your dictionary keys in the appropriate files.

// Header File
extern NSString *const JKSourceArray;
extern NSString *const JKResultsArray;
extern NSString *const JKSomeNumber;

// Implementation File
NSString *const JKSourceArray = @"JKSourceArray";
NSString *const JKResultsArray = @"JKResultsArray";
NSString *const JKSomeNumber = @"JKSomeNumber";

The advantage over using an array is that the the order of elements and the presence/absence of elements doesn't matter, making it far easier to extend in the future, if you want to return additional objects. It's also far more flexible and extensible than passing by reference.