Dynamic global variables in iOS app

Question

I searched the internet and more than 20 topics about global variables, I just couldn't find the one I need.

Will use it in an iOS application.
I want the variable to be accessible from all views.
I want a few views to be able to change that variable.
Preferably don't want to mess with segues.

varibles which are declared in appdelegate wont help you? – KAREEM MAHAMMED Feb 20 '14 at 11:14 — KAREEM MAHAMMED, Feb 20 '14 at 11:14
Do you not like OOP? Do you not like encapsulation? – Abizern Feb 27 '14 at 00:22 — Abizern, Feb 27 '14 at 00:22
I just do not like or understand objective-c – Esqarrouth Feb 27 '14 at 08:04 — Esqarrouth, Feb 27 '14 at 08:04

AntonijoDev · Accepted Answer · 2014-02-20T13:35:14.203

You could do what is suggesting, add a variable in AppDelegate and then fetch it from your view controllers like this:

AppDelegateNeme *ap = (AppDelegateNeme *)[[UIApplication sharedApplication] delegate];
ap.yourVar = smth

As you can see in code above, you are accessing shared instance of UIApplication and just by casting it to your AppDelegate class you can reach your "global" variable. But I personally don't see this as the best solution. What happens is that you need to include your app delegate in every UIViewController, and chances are that you already included that UIViewController in your AppDelegate so you could end up looking at recursive includes or a very messy code.

Cleaner approach would be to create a class to store your global variables, just add a file and for a class choose NSObject. Then you can create singleton object of that class or you can just define class variables and class methods (the one with +) to store and fetc values from your "global vars".

In this way your code will be mode readable and you will never have any include problems, as long as you don't start including stuff in that class.

Example:

//GlobalClass.h
@interface GlobalClass : NSObject

@property (nonatomic) BOOL someBool;

// example wit a singleton obj:
+ (GlobalClass *)globalClass;

// example with class methods
+(int)GetMyVar;
+(void)SetMyVar:(int)var;

//GlobalClass.m
static int MyVar;

@synthesize someBool;

static GlobalClass *globalClass = nil;

+ (GlobalClass *)globalClass
{
    if (globalClass == NULL)
    {
        // Thread safe allocation and initialization -> singletone object
        static dispatch_once_t pred;
        dispatch_once(&pred, ^{ globalClass = [[GlobalClass alloc] init]; });
    }
    return globalClass;
}

+(int)GetMyVar
{
    return MyVar;
}
+(void)SetMyVar:(int)var
{
    MyVar = var;
}

So from outside (from your viewcontroller): To create singleton and set our bool property:

//set var:
[[GlobalClass globalClass] setSomeBool:YES];
// get 
BOOL b = [[GlobalClass globalClass] someBool];

OR use class methods (don't need to create singletone obj)

// set
[GlobalClass SetMyVar:5];
// get
int num = [GlobalClass GetMyVar];

Hope this helps...

Use of undeclared identifier 'globalClass',,,, maybe something missing in this code? what is the difference between singletone obj and class method? it seems class methods are far more simpler, i would prefer to us them unless there are reasons to use singletone obj? — Esqarrouth, Feb 20 '14 at 13:32
You are right, I have edited my answer... Yes you can, expecialy when you just want to save some helper data or global variable which is what you want. Sinletone object is object like any other that you instance from a class, only difference is that you can create it only once. As you can see from my edit it's pointer is stored in an class variable... — AntonijoDev, Feb 20 '14 at 13:42

score 2 · Answer 2 · answered Feb 20 '14 at 11:30

2

In app delegate header

extern NSString* const globalVariable1;

in app delegate m file

NSString* const globalVariable1 = @"My Value";

You can access this global variable in any view controller.

this is just for string.

int const for integer.

just BOOL for boolean.

Hope this helps

answered Feb 20 '14 at 11:30

Bala

510
2
9

1

Read-only variable is not assignable – Esqarrouth Feb 20 '14 at 11:34
You can remove const to assign values. – Bala Feb 20 '14 at 11:35

Esqarrouth · Answer 3 · 2015-01-22T14:33:00.213

For swift I used this method:

struct MyStyles {

static let ThemeColor = UIColor(red: 41/255, green: 156/255, blue: 253/255, alpha: 1.0)
static let ThemeSecondColor = UIColor.whiteColor()
static let ThemeGrayLineColor = UIColor(red: 128/255, green: 128/255, blue: 128/255, alpha: 1.0)
static let ThemeMyCommentsColor = UIColor(red: 219/255, green: 238/255, blue: 255/255, alpha: 1.0)
static let ThemeCommentedToMeColor = UIColor(red: 227/255, green: 232/255, blue: 235/255, alpha: 1.0)

static let ThemeFontName = "HelveticaNeue-Light"
static let ThemeFontNameBold = "Helvetica-Bold"

static let ScreenWidth = UIScreen.mainScreen().bounds.size.width
static let ScreenHeight = UIScreen.mainScreen().bounds.size.height
static let StatusBarHeight = UIApplication.sharedApplication().statusBarFrame.size.height

static func largeButton(#title: String, action: String, target: UIViewController) -> UIButton {

    let button = UIButton(frame: CGRect(x: 0, y: ScreenHeight*9/10, width: ScreenWidth, height: ScreenHeight/10))
    button.setTitle(title, forState: UIControlState.Normal)
    button.backgroundColor = ThemeSecondColor
    button.tintColor = ThemeColor
    button.titleLabel?.font = UIFont(name: ThemeFontName, size: 50)
    button.setTitleColor(ThemeColor, forState: UIControlState.Normal)
    button.addTarget(target, action: Selector(action), forControlEvents: UIControlEvents.TouchUpInside)
    return button
}

}

I access them like this from other classes:

var color = MyStyles.ThemeColor

Why did you tag your question with ObjC and post a Swift answer? Please tag your question appropriately to the language you're working in. — jscs, Dec 25 '14 at 21:40

score 0 · Answer 4 · answered Feb 20 '14 at 11:14

0

You should declare your 'global' variables in your Application Delegate class.

This way you can ensure that all your viewsControllers etc will be able to access them.

For me it's probably the most elegant solution, when you need access to one of these vars you can just get a reference to your app delegate.

answered Feb 20 '14 at 11:14

Woodstock

22,184
15
80
118

examples please? extern? other way? what to do about the error "cant change readonly variables"? – Esqarrouth Feb 20 '14 at 11:17
AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate]; NSString *str = [appDelegate str]; is this the way you are talking about? – Esqarrouth Feb 20 '14 at 11:38
That's one way to do it, yes. Where you have str declared in your app delegate. – Woodstock Feb 20 '14 at 11:50
Why the -1? Putting variables in AppDelegate is perfectly acceptable. – kakubei Apr 02 '15 at 09:34

score 0 · Answer 5 · edited May 23 '17 at 11:56

Create a singleton class. Add all global variables as read/write properties. Create the singleton instance when your app starts, typically inside application:didFinishLaunchingWithOptions: method. Using this singleton instance you can now share information throughout your app.

You may need to thing about making the properties thread safe in case your app will access these in a multithreaded environment.

Hope that helps!

Dynamic global variables in iOS app

5 Answers5

Linked