Question

i’m having NSMutableArray which containing student info, now i just want to extract student name and their average mark only, so what i did

    NSMutableArray *stuCollection = [[NSMutableArray alloc] initWithCapacity:[students count]];

for (int i = 0; i < [students count]; i++) 
{
    if([students objectAtIndex:i] != NULL)
    {

    NSDictionary *dic = [students objectAtIndex:i];
    NSString *temp = [dic objectForKey:@"name"];

    [stuCollection  addObject:name];

    }   
}


for(int j=0; j< [stuCollection count]; j++)
{
    NSLOG(@"Name %@",[stuCollection objectAtIndex:j]);
}

i’m able to run this for first time, but when i make auto scan, i can exe for 1st, 2nd, 3rd loop but then apps terminate show as below,

2009-12-02 14:57:37.908 AppBuzz[13073:207] * Terminating app due to uncaught exception ‘NSInvalidArgumentException’, reason: ‘* -[NSCFArray insertObject:atIndex:]: attempt to insert nil’
2009-12-02 14:57:37.916 AppBuzz[13073:207] Stack: (
820145437,
837578260,
819694387,
819694291,
814683071,
814716415,
814716245,
17529,
24097,
814480795,
819893443,
819891231,
858682228,
861592624,
861585968,
8997,
8860
)
terminate called after throwing an instance of ‘NSException’
Program received signal: “SIGABRT”.

how this can be improve

thanks

Answer 1

Do you understand assertions?

assert(students);
assert([students count]);

NSMutableArray * stuCollection = [[NSMutableArray alloc] initWithCapacity:[students count]];
assert(stuCollection);

for (int i = 0; i < [students count]; i++) {
    if ([students objectAtIndex:i] != NULL) {

        NSDictionary * dic = [students objectAtIndex:i];
        assert(dic);

        NSString * temp = [dic objectForKey:@"name"];
        assert(temp);

        assert(name);

        [stuCollection addObject:name];
    }
}
...