Question

I am learning Objecive-C and try to removeObject method in loop.
It is not work correctly. I recive “Thread 1: Program received signal:”SIGABRT”.” on that line.
What is wrong?

NSMutableArray *bookListMutable = [NSMutableArray arrayWithObjects:@"TitleM 2", @"TitleM 4", @"TitleM 5", nil];
[bookListMutable addObject:@"TitleM 3 added"];
[bookListMutable insertObject:@"TitleM 1 inserted" atIndex:0];

long countMutable;
countMutable = bookListMutable.count;


for(int y = 0; y < countMutable; y++){
    [bookListMutable removeObject:[bookListMutable objectAtIndex:y]];
}

P.S. xCode 4.1

Answer 1

You should not remove items in that order. Let’s say the array has 4 items {0, 1, 2, 3} and simulate the execution of the program:

1. First iteration with y = 0: removing item at index 0 from {0, 1, 2, 3} gives {1, 2, 3}.

2. Second iteration with y = 1: removing item at index 1 from {1, 2, 3} gives {1, 3}

3. Third iteration with y = 2: removing item at index 2 from {1, 3} gives. Oops, there is no item at index 2 => Exception.

So you should iterate backwards like this:

for(int y = countMutable-1; y >= 0; y--) {
    [bookListMutable removeAtIndex:y]];
}

or use the build in method:

[bookListMutable removeAllObjects];