Adding objects to a NSMutableArray property

Question

this is my data strucure:

group [1...n] {
  id,
  name,
  elements : [1...n]
}

I define a class for element with all properties and a class for group as:

@interface Group : NSObject {    
    NSInteger groupID;
    NSString *groupName;        
    NSMutableArray *elements;       
}

@property (assign, readwrite) NSInteger groupID;
@property (assign, readwrite) NSString *groupName;
@property (assign, readwrite) NSMutableArray *elements;

and single element with:

@interface Element : NSObject {
    NSInteger elementID;
    NSString *elementName;
}
@property (assign, readwrite) NSInteger elementID;
@property (assign, readwrite) NSString *elementName;

Both classes have properties and synthesize. When application start I inserted data on data structure with this:

arrGroup = [NSMutableArray array];
[arrGroup retain];
Element *element1 = [[Element alloc] init];
element1.elemenID = 1;
element1.elemenName = @"Andrea";

Element *element = [[Element alloc] init];
element2.elementID = 2;
element2.elementName = @"Andrea2";

Group *group = [[Group alloc] init];    
group.groupID = 1;
group.groupName = @"Grup 1";    
[group.elements addObject:element1];
[group.elements addObject:element2];

[contact1 release];
[contact2 release];

[arrGroup addObject:group];

The problem is this the [group.elements addObjct:element1]. Nothing has been written on elements NSMutableArray.

Could you help me to find the error? There is a better method to retrieve structure data (groups of elemens)?

thanks for help! Andrea

Could you add the property declarations and the code that initializes elements? — Georg Fritzsche
– Georg Fritzsche, Commented Jul 12, 2010 at 19:08
At this point I suppose you found the problem! I actually initialize the elements but I just added a NSMutableArray *elements; to group object definition. I thought that @synthesize is enough. I don't know how to initialize the elements Mutable Array of objects elements — Andrea Girardi
– Andrea Girardi, Commented Jul 12, 2010 at 19:48

Georg Fritzsche · Accepted Answer · 2010-07-12 20:37:30Z

15

@synthesize only generates the getter and the setter for your property, you have to take care of initialization yourself if needed.

To initialize the mutable array do e.g. this in your initializer:

- (id)init { // or however it is named
    if ((self = [super init])) {
        elements = [[NSMutableArray alloc] init];
        // ... more?
    }
    return self;
}

- (void)dealloc {
    [elements release]; // don't forget to clean up
    // ... more?
    [super dealloc];
}

answered Jul 12, 2010 at 20:37

Georg Fritzsche

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1 Comment

Andrea Girardi Over a year ago

Great it works!!!!!! Thanks!!! (I wrongly defined the init, for this reason I didn't include... I've to return to the books.... :( )

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