NSMutableArray can not add object?

Question

I have 2 model:

@interface Program : NSObject

@property (nonatomic, retain) NSString * name;

@property (nonatomic, strong) NSMutableArray *guides;
@end

@interface Guide : NSObject
@property (nonatomic, retain) NSString *name;
@end

And I add some guides to program from one xml:

    Program *program = [Program new];
    program.name = @"My list"
    for(DDXMLElement *guideElement in [programElement nodesForXPath:@"guide" error:&error])
    {
        Guide *guide = [Guide new];
        guide.name = [guideElement stringValue];// [p attribute:@"name"];
        [program.guides addObject:guide];
        NSLog(@"load guide number: %d", [program.guides count]);
    }

The out is always "load guide number: 0"

Have you created the NSMutableArray? Such as: self.guides = [NSMutableArray array] — HKTonyLee
– HKTonyLee, Commented Dec 21, 2012 at 3:25
Because callling any method of nil object will return nil value. In this case, [program.guides count] will return 0. — HKTonyLee
– HKTonyLee, Commented Dec 21, 2012 at 3:26

Hot Licks · Accepted Answer · 2012-12-21 03:24:58Z

2

program.guides is nil, since you never created it.

answered Dec 21, 2012 at 3:24

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1 Comment

why Over a year ago

Thank you very much, it works after I add NSMutableArray *guides = [NSMutableArray new]; and program.guides = guides;

Aaron Brager · Accepted Answer · 2012-12-21 03:29:40Z

1

In your Program's init method, add:

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

Or, more sloppily, before your for loop add:

program.guides = [[NSMutableArray alloc] init];

answered Dec 21, 2012 at 3:29

Aaron Brager

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