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I am very new to Objective C and stumbled upon this problem. How is it possible to create a global instance of a class in Objective C which is accessible from multiple classes and the main function?

Matias Frank Jensen
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    possible duplicate of [objective-c - global variables](http://stackoverflow.com/questions/8808159/objective-c-global-variables) – edtheprogrammerguy Jul 04 '14 at 16:39
  • Duplicate of http://stackoverflow.com/questions/8808159/objective-c-global-variables – edtheprogrammerguy Jul 04 '14 at 16:39
  • @dasblinkenlight that one is not thread-safe. The current recommended method is to use `dispatch_once`, otherwise you can use `@synchronized`. See http://www.galloway.me.uk/tutorials/singleton-classes/ – jcaron Jul 04 '14 at 17:02
  • @jcaron You are right - I linked an older answer. [Here is a more modern answer showing how to make a singleton](http://stackoverflow.com/a/11945106/335858). Thanks! – Sergey Kalinichenko Jul 04 '14 at 17:05

3 Answers3

2

You can do it in this way:

+(MyClass *) sharedInstance
{
    static id sharedInstance = nil;
    @synchronized(self)
    {
        if (!sharedInstance)
        {
            sharedInstance = [[MyClass alloc] init];
        }
        return sharedInstance;
    }
}

Just access the object by this single line of code:

[MyClass sharedInstance]

Hope it helps!! Happy Coding :)

Sahil Mahajan
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1

Add a method to your class that returns this specific instance.

The most common case is the singleton. You can also look up "shared instance".

jcaron
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-1

You can use singleton, import the .h file in your .pch file, by doing that every file will have this imported :

YourClass.h : 

@interface YourClass : NSObject

/**
 * Method to get the singleton instance
 * @return Instance of YourClass 
 */
+ (YourClass *)instance;
@end

YourClass.m :

#import "YourClass.h"

@interface YourClass(){

}
@end

#pragma mark -

@implementation YourClass

- (id)init{
    //prevents normal inits
    return nil;
}

+ (YourClass *)instance
{
    static YourClass *instance = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        instance = [[self alloc] initSingelton];
    });
    return instance;
}

- (id)initSingelton{
    if (self = [super init]) {
        //do stuff here
        return self;
    }
    return nil;
}
Moti F.
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