How do you transfer an array from class to class in Objective-C?

Question

As one might expect I'm new to Objective-C and Cocoa2d so this might be painfully obvious but I can't seem to get it to work in a way that makes sense.

What I'm trying to do is to make an array of 10 members (more will be added later) full of either [0,1,2,3] integers, later I want these numbers to be used for a level selection screen where 0 means the level is locked (not completed), and the numbers >0 represent the number of stars (out of three) and mean the level was completed, at the end of a level I want to change the array to reflect that the level was completed. For testing purposes I filled the array with "random integers" (0-3) as such (in LevelSelection.m):

NSMutableArray *LevelCompArray = [NSMutableArray arrayWithCapacity:10];
        for(int i = 0; i<10; i++){
            int x= (arc4random() % (4));
            [LevelCompArray addObject:[NSNumber numberWithInteger:x]];
        }

I have not alloced nor init the Array but it seems to work within the function itself -(id) init though I believe that is a the root of my problem.

My problem is simple, how do I transfer this array (and other data I will create as my game progresses) from class to class (e.g. from LevelSelection.m to LevelCompleted.m) and from function to function (e.g. -(id) init and -(void) launchLevel). Do I have a centralized file for data that all required classes can access? If that's the case what's with all the talk of a ".plist"? If not, do I transfer the data through methods to the target class(es)/ method(s)? How do I do that?

Any help is deeply appreciated, transferring me to a tutorial would also be incredibly useful.

score 2 · Answer 1 · edited May 23 '17 at 10:27

you shoukld use a property for the array. like that: first you need to create the array in the secondviewcontroller.h, like this:

    NSMutableArray *LevelCompArray;
    @property (nonatomic, retain) NSMutableArray *LevelCompArray;

then synthesize it in the secondviewcontroller.m:

@synthesize LevelCompArray;

Then, for example, you want to pass Array when a button in FirstViewController is touched. In its action, you can set it to get the instance of your second view controller, like that:

secondViewController.LevelCompArray = someArray;

actually it is passing data between viewcontroller, for more info check this link: Passing Data between View Controllers

hope this help.

You don't need that first line "NSMutableArray *LevelCompArray;" in your first code sample. — Jesse Rusak, Jul 13 '12 at 21:02

score 2 · Accepted Answer · answered Jul 13 '12 at 21:07

One way to do it would be, as you said, have a bunch of global variables in a file that everyone #imports. You wouldn't use a .plist file; rather, it would just be a .m like all your other source code.

You could also pass the information to the constructor of any object that needs it. For example, you could do something like [[LevelSelection alloc] initWithCompletionArray:LevelCompArray]. Then, to make sure that every object has the right information in said array, use notifications.

-(id) initWithStuff:(Stuff *s) {
    if(self = [super init]) {
        [[NSNotificationCenter defaultCenter] addObserver:self
                                                 selector:@selector(doStuff:)
                                                     name:@"LEVEL_COMPLETED"
                                                   object:anObject];
    }

And then in doStuff: (which takes an NSNotification*), you'd have some logic to handle whatever happened, using the notification's object.

How do you transfer an array from class to class in Objective-C?

2 Answers2