I need to make one instance of an array that can be access by multiple view controllers

Question

I need to make one instance of an array that can be access by multiple view controllers. It will contain objects that will be displayed in a table view and created by a modular view and then displayed in the table view. I can't figure out how to access it once I make a @property for it in the main view controller or the AppDelegate class.

Answer 1

You should make a singleton and the recommended way to do that in objective-c is to create a class and add a method that looks something like:

+ (YourClass *)sharedYourClass
{
    static dispatch_once_t onceToken;
    static YourClass       *sharedInstance;

    dispatch_once(&onceToken, ^{
        sharedInstance = [[self alloc] init];
    });

    return sharedInstance;
}

Put the array as a property in your class.

//YourClass.h
@interface YourClass : NSObject

@property(nonatomic, strong)NSArray *yourArray;

+(YourClass *)sharedYourClass;

@end

And in every class you want to use your singleton start by importing YourClass.h and then use it like:

NSArray *arr = [YourClass sharedYourClass].yourArray;
[YourArray sharedYourClass].yourArray = [[NSArray alloc] init];
etc..

Answer 2

What I do is put the data I want shared, in your instance the array, in the AppDelegate. Then I define a protocol that the app delegate conforms to. This lets me access the data anywhere. For example, say I have an array I want everywhere:

First define a protocol:

    @protocol ApplicationState<NSObject>

    @property(nonatomic, strong) NSArray* data;

    @end

Then make your app delegate conform to it:

    @interface AppDelegate : UIResponder <UIApplicationDelegate, ApplicationState>

    @property (strong, nonatomic) UIWindow *window;

    @property(nonatomic, strong) NSArray* data;

    @end

Then reading and writing this shared object is simple:

    id<ApplicationState> appState = (id<ApplicationState>) [UIApplication sharedApplication].delegate;
    appState.data = [[NSArray alloc] init];

Answer 3

I am going to assume you can make the class of the array inherit from NSObject, and then pass it to the View Controller from there...

Answer 4

You have 2 ways to do this:

1.- Instantiate 1 arra on the main class and pass the reference to each viewcontroller what you need.

2.- Make a singleton class to hold the array an use this in your project.

Answer 5

First create a class like this

//GlobalDataClass.h
@interface GlobalDataClass : NSObject
@property(nonatomic,retain)NSArray *myArray;
+(GlobalDataClass*)getInstance;
@end


#import "GlobalDataClass.h"
//GlobalDataClass.m
@implementation GlobalDataClass
@synthesize myArray;

static GlobalDataClass *instance =nil;

+(GlobalDataClass *)getInstance
{
    @synchronized(self)
    {
        if(instance==nil)
        {
            instance = [GlobalDataClass new];
        }
    }

    return instance;
}
@end

Then you can use it in your viewControllers like this:

-(void)viewDidLoad{
    [super viewDidLoad];
    self.dataObj = [GlobalDataClass getInstance];
    NSLog(@"%@",self.dataObj.myArray);
}

Hope it helps!