Question

I am new to Objective C and here is my confusion:

When is it applicable to allocate memory for an instance?. Like this:

When is it applicable to use this…

NSString *str = [[NSString alloc]init];

and to use this…

- (NSString *) formatStr:(NSString *) str{
   NSString *str = (NSString *) str;
...
.....
.......
}

and even creating UIActionSheet, it uses alloc but in other UI elements, it does not..

What exactly the reason and when shall it be done?

Thanks fellas.. 😀

Answer 1

In addition to the “normal” allocation route (i.e. through [[MyClass alloc] init]) some classes provide so called “factory methods”. These are class methods that allocate objects internally. The advantage of using factory methods is that they can create a suitable subclass to return to the caller. In both cases, though, the allocation is ultimately done by alloc/init.