IOS: the correct way to create object-c singleton

There are many wrong ways to create singleton class on the web, there is the right way to create it.

//  MyManager.h

#import

@interface MyManager : NSObject

+ (MyManager*) sharedManager;

@end

//  MyManager.m

#import "MyManager.h"

@implementation MyManager

static  MyManager* sharedInstance = nil;

+ (MyManager*) sharedManager {

    if(sharedInstance==nil) {

        @synchronized(self) {

            if (sharedInstance==nil) {

                sharedInstance = [[MyManager alloc] init];

            }

        }

    }

    return sharedInstance;

}

- (id)init {

    if (self = [super init]) {

        //init some properties here

    }

    return self;

}

@end