Question

I have tried to initialize my NSMutableArray 100 ways from Sunday, and NOTHING is working for me. I tried setting it equal to a newly allocated and initialized NSMutableArray, just allocating, initializing the variable by itself, every combination I could think of and always the same result.

Here’s the code:

Object.h

NSMutableArray *array;

@property (copy) NSMutableArray *array;

Object.m

@synthesize array;

if ( self.array ) {
    [self.array addObject:anObject];
}
else {
    self.array = [NSMutableArray arrayWithObjects:anObject, nil];
}

NOTE: In debug "anObject" is NOT nil at time of execution…

I have tested anObject and it isThe initialization works just fine, but I keep getting the error below when I try to addObject: to self.array.

2010-07-10 11:52:55.499 MyApp[4347:1807] -[__NSArrayI addObject:]: unrecognized selector sent to instance 0x184480

2010-07-10 11:52:55.508 MyApp[4347:1807] *** Terminating app due to uncaught exception
‘NSInvalidArgumentException’, reason: ‘-[__NSArrayI addObject:]: unrecognized selector sent to instance 0x184480’

Does anyone have any idea what’s going wrong?

Answer 1

I would like to tip my hat to Georg Fritzsche. I did end up needing to use (copy) instead of (retain), and I would not have known what to do without his input.

//@property (copy) NSMutableArray *array;
@property (nonatomic, copy) NSMutableArray *array; //overridden method is non-atomic as it is coded and should be reflected here.

If you wish to use (copy) on a mutable object you must override the “setter” method as follows…

- (void)setArray:(NSArray *)newArray {

    if ( array != newArray ) { 
        [array release];
        array = [newArray mutableCopy];
//      [array retain]; // unnecessary as noted by Georg Fritzsche
    }

    return;
}

NOTE: You will get a compiler warning: Incompatible Objective-C types initializing ‘struct NSArray *’, expected ‘struct NSMutableArray *’ I chose to declare the newArray parameter as an (NSArray *), because you are given the flexibility to have any array passed and correctly copied to your (NSMutableArray *) variable. If you wish to declare the newArray parameter as an (NSMutableArray *) you will still need to leave the mutableCopy method in place to get your desired results.

Cheers to Georg!
Z@K!