Creating global Variables and Objects in Objective C

Question

I am new to objective-C and working on an app in which there are multiple viewController Files. I need to access Value of variables set in one file to be accessible in other files. How can i implement this.

What i was doing that i created a class Globals.m and declared variables in it.

#import <Foundation/Foundation.h>

@interface Globals : NSObject

@property  NSString*  firstName;
@property NSString* lastName;
@property NSString* emailId;

@end

My question are: 1.will the above Declaration make these variables retain there values in different files?

Where should i crete a object of this class which should be accessible in all files.

You can remove the @property annotation... (It's just for generating getter/setter methods.) Then, use #import to import this file wherever you want to use the variables. — martin jakubik, Apr 02 '15 at 07:05
after removing @property it is giving error cannot declare variable inside interface — Junior Bill gates, Apr 02 '15 at 07:07
Hmm, you know what? Just get rid of @interface (and @end). There is no need for annotations in this file because you're just declaring some constants. — martin jakubik, Apr 02 '15 at 07:09
@martinjakubik I removed (@interface) and it dont gave error now. can u plz tell me that how can i create a global object — Junior Bill gates, Apr 02 '15 at 07:13
If you want an object (my answer does not create a class... just a flat file), then Popeye's answer is better. — martin jakubik, Apr 02 '15 at 07:16
possible duplicate of [Using global variables in Objective-C](http://stackoverflow.com/questions/19604523/using-global-variables-in-objective-c) — Burhanuddin Sunelwala, Apr 02 '15 at 07:24

score 2 · Answer 1 · edited May 23 '17 at 11:50

2

I'd maybe suggest using a Singleton pattern as it will allow you to hold an instance of the class through your app. So you could set firstName in one class and get it in another.

MySingleton.h

@interface MySingleton : NSObject

// Our properties we want to set.
@property (nonatomic, strong) NSString *firstName;
@property (nonatomic, strong) NSString *lastName;
@property (nonatomic, strong) NSString *emailName;
// etc...

// Our class method for getting the shared instance.
+ (MySingleton *)sharedInstance;

@end

MySingleton.m

#import "MySingleton.h"

@implementation MySingleton

+ (MySingleton *)sharedInstance
{
    static dispatch_once_t pred = 0;
    static id sharedObject = nil;
    dispatch_once(&pred, ^{
        sharedObject = [[self alloc] init];
    });

    return sharedObject;
}

@end

Then in your other classes all you need to do is import the MySingleton class and do something like :

MySingleton *singleton = [MySingleton sharedInstance];
[singleton setFirstName:@"Bob"];

For more information on Singleton Patterns and other Design Patterns here is a tutorial that you could read through iOS Design Patterns. Also a good read is Correct Singleton Pattern Objective C (iOS)?

edited May 23 '17 at 11:50

Community

1
1

answered Apr 02 '15 at 07:15

Popeye

11,839
9
58
91

After this how can i access sharedObject in other files – Junior Bill gates Apr 02 '15 at 07:18
See the edit I have just done. All you need to do is call the class method something like `MySingleton *singleton = [MySingleton sharedInstance];` and then you can access all the properties it has. – Popeye Apr 02 '15 at 07:20
variables when accessed in different in different files will retain there value?? – Junior Bill gates Apr 02 '15 at 07:22
@Popeye you still need #import, no? (Assuming your classes are in different files...) – martin jakubik Apr 02 '15 at 07:23
@martinjakubik Yes sorry I'll update with that but I normally assume imports are a given. – Popeye Apr 02 '15 at 07:24
@JuniorBillgates Yes they will retain there values. – Popeye Apr 02 '15 at 07:25
@Popeye yes, I see. It's up to you... It's just that this question is about such a basic mechanism that maybe it warrants showing the whole file in the examples. – martin jakubik Apr 02 '15 at 08:04

Creating global Variables and Objects in Objective C

1 Answers1