Global Property- objective c

Question

I'm making an program, and it requires that properties in one View Controller be accessible by all classes. How would I make a global property?

Answer 1

A couple of options:

1. Ideally, you should avoid making it a global, but rather pass the property from one view controller. See this excellent answer for examples (such as setting it in prepareForSegue).

2. Alternatively, you can create a singleton, and make your property of that singleton. For example, Model.h:

   //  Model.h
   
   @import Foundation;
   
   NS_ASSUME_NONNULL_BEGIN
   
   @interface Model : NSObject
   
   @property (class, strong, readonly) Model *sharedModel;
   
   @property (nonatomic, copy, nullable) NSString *myString;
   
   - (id)init __attribute__((unavailable("Use +[Model sharedModel] instead")));
   + (id)new __attribute__((unavailable("Use +[Model sharedModel] instead")));
   
   @end
   
   NS_ASSUME_NONNULL_END
   

   and Model.m

   //  Model.m
   
   #import "Model.h"
   
   @implementation Model
   
   + (instancetype)sharedModel {
       static id sharedMyModel = nil;
       static dispatch_once_t onceToken;
       dispatch_once(&onceToken, ^{
           sharedMyModel = [[self alloc] init];
       });
       return sharedMyModel;
   }
   
   @end
   

   and then your various controllers can use this singleton class and reference that property you need accessible from other classes, such as:

   #import "SomeViewController.h"
   #import "Model.h"
   
   @implementation SomeViewController
   
   - (void)viewDidLoad {
       [super viewDidLoad];
   
       Model *model = [Model sharedModel];
   
       model.myString = @"abc";
   }
   
   @end
   

   and

   #import "AnotherViewController.h"
   #import "Model.h"
   
   @implementation AnotherViewController
   
   - (void)viewDidLoad {
       [super viewDidLoad];
   
       NSString *string = [[Model sharedModel] myString];
   
       // Do whatever you want with the string
   }
   
   @end
   

3. Your app actually already has a singleton, the app delegate, and you could add a property to that, and use that. For example, if you defined a property, someOtherString in the app delegate's .h, you could then reference it like so:

   AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];
   appDelegate.someOtherString = @"xyz";
   

   If I'm going to use a singleton for model data, I prefer to create my own, but this is another approach that some people use.