Question

I know Apple is big on having you use NS objects instead of true primitive types, but I need the capabilities of an array (namely direct access of items at indices). However, it seems that they are so very keen on using NS objects that I can’t find a single tutorial online or in a textbook about how to use basic primitive arrays. I want something that does things like this does in Java:

String inventory[] = new String[45];

inventory[5] = "Pickaxe";
inventory[12] = "Dirt";
inventory[8] = "Cobblestone";

inventory[12] = null;

System.out.println("There are " + inventory.length + " slots in inventory: " + java.util.Arrays.toString(inventory));

The following is the closest I’ve gotten in Objective-C, but it won’t run properly:

NSString *inventory[45];

inventory[5] = @"Pickaxe";
inventory[12] = @"Dirt";
inventory[8] = @"Cobblestone";

inventory[12] = nil;

NSArray *temp = [NSArray arrayWithObjects:inventory count:45];
NSLog(@"There are %i slots in inventory: %@", [temp count], [temp description]);

Also, if at all possible, is there something in O-C that will give me the count of non-null/non-nil objects in the array? (This way, I can tell how much space is left in the inventory so that the player can’t pack away anything if it’s full)

Answer 1

typically, you would use NSArray/NSMutableArray, although you could also use C arrays.

NSArray (and most Foundation collections) cannot contain nil entries – you can use NSPointerArray (OS X) if you need nil values, or simply use [NSNull null] in an NSArray to designate nil.

Here’s your program using an NSArray:

NSMutableArray * inventory = [NSMutableArray array];
for (NSUInteger idx = 0; idx < 45; ++idx) {
  [inventory addObject:[NSNull null]];
}

[inventory replaceObjectAtIndex:5 withObject:@"Pickaxe"];
[inventory replaceObjectAtIndex:12 withObject:@"Dirt"];
[inventory replaceObjectAtIndex:8 withObject:@"Cobblestone"];

[inventory replaceObjectAtIndex:12 withObject:[NSNull null]];

NSArray *temp = [NSArray arrayWithObject:inventory];
NSLog(@"There are %i slots in inventory: %@", [temp count], [temp description]);

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Also, if at all possible, is there something in O-C that will give me the count of non-null/non-nil objects in the array?

An NSArray is a CFArray – they are “toll free bridged”. Use CFArrayGetCountOfValue with [NSNull null] as the value to seek. Most of the CF-APIs are available in the NS-APIs, but not this one. You could easily wrap it in a category, if needed often.