Question

I’m using a NSDateFormatter object (customized for specific purposes) multiple times. Since I’m not a objc expert, I figured out three different approaches to deal with it.

In the first one, I’ve created a NSDateFormatter category and customized the code there. This is common approach but each time I create such an object, this is put in the main autorelease pool. This behaviour, I think, is valid both for non-ARC and ARC code.

In the second instead, I’ve overridden the +(void)initialize method and put the customization code there. Here a simple example:

static NSDateFormatter* dateFormatter = nil;

+(void)initialize
{
    dateFormatter = [[NSDateFormatter alloc] init];
    // other code here
}

Finally, I set up a third approach using a lazy loading instantiation through properties like the following:

-(NSDateFormatter)dateFormatter
{
    if(dateFormatter) return dateFormatter;        
    // alloc-init here
}

Said this, I would like to know what approach is the most suitable to deal with objects multiple times and if, using +(void)initialize in that manner, is correct.

Thank you in advance.

Answer 1

Both later methods are correct, but I believe you want to put them together!

static NSDateFormatter *sharedInstance = nil;

+ (NSDateFormatter *)sharedInstance {
    if (sharedInstance == nil) {
        sharedInstance = [[NSDateFormatter alloc] init];
    }
    return sharedInstance;
}

Note: Such classes are called singletons. Read more