Question

Best related discussions I’ve turned up: Making an array of Objects in Objective-C.. Scanned through links that came up when I prepped this post.

Self-study mode, creating mini-apps to reinforce and extend ideas I get working on book tutorials.
…………….

Goal: To store some number of objects (example class ‘Trip’) in a mutable array, contained in another object (example class ‘TourCompany’).

(portions of the two different class interface files)

    @interface Trip : NSObject
    @property (strong, nonatomic) NSString *travelToLocation;

……

        @interface TourCompany : NSObject
        @property (strong, nonatomic) NSMutableArray *trips ;

…… CODE AND GOAL IN PIECES….

1) Demonstrate that I created 3 trip objects and can access the travelToLocation ivar
….

        Trip *trip0 = [[Trip alloc] init];
        Trip *trip1 = [[Trip alloc] init];
        Trip *trip2 = [[Trip alloc] init];

        [trip0 setTravelToLocation:@"Vienna"];
        [trip1 setTravelToLocation:@"Mt. St. Helens"];
        [trip2 setTravelToLocation:@"Tenochtitlan"];

        NSString *somePlace1 = trip1.travelToLocation;

        NSLog(@" %@ %@, \n \t Let's LOOK at one particular trip ivar %@.", twoBlanks, nuLn, somePlace1);

     //  CONSOLE RESULTS
      //     Let's LOOK at one particular trip ivar Mt. St. Helens.

….
2) Demonstrate that I
i) can store these 3 trip objects in a locally declared NSMutable Array
ii) can access the travelToLocation ivar
….

     // put trip objects into a LOCALLY DECLARED mutable array
        NSMutableArray *localTripsArray = [NSMutableArray array ];

      //[myArray addObject: someOtherPerson]; - compare to a STackOverflow discussion

        [localTripsArray addObject:trip0];
     [localTripsArray addObject:trip1];
        [localTripsArray addObject:trip2];


        for (Trip *t in localTripsArray) {

            NSLog(@"\n \t ^^^Trip location in LOCAL TRIPS Mutable ARRAY is %@", t.travelToLocation );

     }



    /*
        CONSOLE RESULTS
     objectInMutableArrayMiniAppChallenge[521:f803] 
        ^^^Trip location in LOCAL TRIPS Mutable ARRAY is Vienna
2012-07-05 13:47:17.172 objectInMutableArrayMiniAppChallenge[521:f803] 
        ^^^Trip location in LOCAL TRIPS Mutable ARRAY is Mt. St. Helens
        2012-07-05 13:47:17.172 objectInMutableArrayMiniAppChallenge[521:f803] 
         ^^^Trip location in LOCAL TRIPS Mutable ARRAY is Tenochtitlan

        */

….
3) BUT I cannot figure out why I am not storing these 3 objects an NSMutable Array (‘trips’) in an instance of my TourCompany class (‘friendlySkiesTourCo’)
…
// NOW instantiate an object in my TourCompany class

    TourCompany *friendlySkiesTourCo = [[TourCompany alloc] init];

 // put those same objects into the trips ivar in that object
 //[myArray addObject: someOtherPerson]; 
    //     - compare to a STackOverflow discussion
    //only difference I see is that instead of locally declared 'myArray'
    //   I'm using an ivar that's a member of an object
 // I know there's are values in those objects, because I displayed them above


 [friendlySkiesTourCo.trips addObject:trip0];
    [friendlySkiesTourCo.trips addObject:trip1];
    [friendlySkiesTourCo.trips addObject:trip2];


    for (Trip *t in friendlySkiesTourCo.trips) {

NSLog(@”\n \t +++ Trip location in ‘trips’ mutable array in the object ‘friendlySkiesTourCo’, a TourCompany class object, is %@”, t.travelToLocation );

    }


    /* Console NON-Results

    I never get any output from this NSLog directive
     I'll bet there is something pretty basic I don't understand
     No doubt, it's in the Gol Durned Manual online , but I'm not seeing it
     */

….
4. Let’s just double check that the problem is possibly a setting type problem
….
// I don’t think I’m really putting the objects into this particular mutable array in the friendlySkies object correctly
// Let’s just check

 int howManyTripsInMutableArray = [friendlySkiesTourCo.trips count];

 NSLog(@"\n \tThere are %d trips for the friendlySkiesTour Co ", howManyTripsInMutableArray);

        /*

     Sure enough...

     2012-07-05 13:53:53.235 objectInMutableArrayMiniAppChallenge[555:f803] 
    There are 0 trips for the friendlySkiesTour Co 

    */

Thanks for any clues. I hope that I did this writeup succinctly and that you don’t think I just didn’t RTGDM (that’s ‘gol durn’ in case you wondered), because I sure tried to.

Laurel

Answer 1

I’m willing to bet you didn’t initialize friendlySkiesTourCo.trips. ie

friendlySkiesTourCo.trips = [[NSMutableArray alloc] init];

EDIT

As @Chuck pointed out below in the comments, this allocation should really be done in the initializer method for the class:

@implementation TourCompany

-(id) init
{
    self = [super init];

    self.trips = [[NSMutableArray alloc] init];

    return self;
}