#sharedinstance

import Foundation

let sharedInstance = AppSingleton();

final class AppSingleton{       

var aSharedVariable:NSMutableString!       

private init(){}

The Singleton Pattern is one of must used patterns in Objective-C. 

If you are a Objective-C developer, of course you have seen the singleton pattern.

[UIApplication sharedApplication]

[NSBundle mainBundle]

[NSUserDefaults standardUserDefaults]

Do you know them?

they are class methods (they starts with "+"); they will return the (unique) shared instance of an object; they are singletons!

That's all!

Well, below is explained how to create a singleton for your custom class.

First sign your .h file with a class method +(id)sharedInstance;. It must return a object (id is ok!).

#import <Foundation/Foundation.h> @interface MyCustomClass : NSObject +(id)sharedInstance; @end

Second implement the +(id)sharedInstance method into the .m file. It will create the (shared) instance only one time and always return it.

+ (id)sharedInstance { static MyCustomClass *theSharedInstance = nil; static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ theSharedInstance = [[self alloc] init]; }); return theSharedInstance; }

That's really all!