Question

I am using one NSMutableArray with same string object.

Here is the code

NSMutableArray *arr = [[NSMutableArray alloc]initWithObjects:@"hello",@"hi",@"hi",@"hi",@"hi",@"hi",@"hi",@"hi",@"hi",@"hi",@"hi",@"hi",@"hi",nil];
NSObject *obj = [arr objectAtIndex:2];    
[arr removeObject:obj];       
NSLog(@"%@",arr);

When i try to remove 3rd object of array, its removing all object with “hi” string.
I am not getting why its happening.
my doubt is while removing object, NSMutableArray match string or address.

Answer 1

It’s because you’re using removeObject which removes all objects that are “equal” to the one you pass in. As per this Apple documentation:

This method uses indexOfObject: to locate matches and then removes
them by using removeObjectAtIndex:. Thus, matches are determined on
the basis of an object’s response to the isEqual: message. If the
array does not contain anObject, the method has no effect (although it
does incur the overhead of searching the contents).

You’re seeing the effects of literal strings here where each of those @"hi" objects will turn out to be the same object just added many times.

What you really want to do is this:

NSMutableArray *arr = [[NSMutableArray alloc]initWithObjects:@"hello",@"hi",@"hi",@"hi",@"hi",@"hi",@"hi",@"hi",@"hi",@"hi",@"hi",@"hi",@"hi",nil];
[arr removeObjectAtIndex:2];
NSLog(@"%@",arr);

Then you’re specifically removing the object at index 2.