iphone - How to create singleton class in objective C

Question

How can I create a singleton class in Objective C?

Answer 1

Okay appDev, you will probably find quite a few different techniques to do this on the web. However, for iOS app development, I think the most convenient way is to do the following:

• Write your method(s) for getting the singleton object. (Recommendation: use dispatch_once thread and GCD for this).

• Wrap your method(s) in a macro and add it to your $Project$-Prefix.pch file.

• Call the one line macro whenever you need singleton object for a class.

Example:

CommonMacros.h:

#define SINGLETON_FOR_CLASS(classname)
+ (id) shared##classname {
    static dispatch_once_t pred = 0;
    static id _sharedObject = nil;
    dispatch_once(&pred, ^{
        _sharedObject = [[self alloc] init];
    });
    return _sharedObject;
}

YourProject-Prefix.pch:

...
#import "CommonMacros.h"
...

YourSingletonClass.m:

...
SINGLETON_FOR_CLASS(YourSingletonClass)
...