NSMutableDictionary Being accessed from different classes

Question

Hey all,

So, in my iPhone app I was using integers to keep track of a lot of variables. I declared and initialized them all in my AppDelegate file (it's a multiview app), and then if I declared them in the other views (classes) and the values would stay the same. In this way, I could set Money = 200 in the App Delegate file, and then in another view just declare, "int Money;" and it would be set to 200 already (or whatever Money happened to be.)

However, if I'm storing all these variables in a Dictionary (which I am doing now), how can I access that dictionary from different classes/views? I can't simple "declare" it again, I've already tried that. I think it has to do with the dictionary being an object, and so it needs to be referenced or something....

I need to be able to access the same dictionary from all the different views.

#import "SheepAppDelegate.h"

@implementation SheepAppDelegate

@synthesize window;
@synthesize rootController;

//Initialize the Dictionary to store all of our variables

NSMutableDictionary *theHeart;



- (void)applicationDidFinishLaunching:(UIApplication *)application {    

    //Set the values for the Variables and Constants, these are
   //accessed from the different classes.

    NSMutableDictionary *theHeart = [[NSMutableDictionary alloc] init];


    [theHeart setObject:[NSNumber numberWithInt:200] forKey:@"Money"];
    [theHeart setObject:@"Number two!" forKey:@"2"];


    [window addSubview:rootController.view];
    [window makeKeyAndVisible];
}

Initialize the dictionary and adding stuff to it works fine, but in another class...

#import "OverviewController.h"


@implementation OverviewController

@synthesize lblMoney;
@synthesize lblSheep;
@synthesize lblWool;
@synthesize lblFatness;
@synthesize lblCapacity;
@synthesize lblShepherds;

int varMoney;

NSMutableDictionary *theHeart;

- (void)viewWillAppear:(BOOL)animated
{

    varMoney = [[theHeart objectForKey:@"Money"] intValue];


}

You can see I try iniializing the dictionary again for this class, but that obviously itsn't working. I just want to Initialize and setup the dictionary once, in the AppDelegate file, and then access that dictionary from the other classes to change stuff in it. Is there a way to do this? Thanks!

Answer 1

You can either put it in your AppDelegate or create a Singleton. This article covers this topic and many of the possible options including the two I mentioned.

Singletons seem to be the more organized method. You can store all of your global information in one and you'll be able to access it from anywhere.

Answer 2

Make your NSMutableDictionary instance static and write a class method to access it. Put this in your SheepAppDelegate.m:

static NSMutableDictionary *theHeart;
+ (NSMutableDictionary*)theHeart
{
    if (theHeart == nil) theHeart = [[NSMutableDictionary alloc] init];

    return theHeart;
}

And access it anywhere else by using:

NSMutableDictionary *dict = [SheepAppDelegate theHeart];

Answer 3

There's no good reason not to just pass the dictionary along to your controller as a reference. If you create an NSMutableDictionary ivar in your OverviewController making it a property, you can then set the dictionary there when you create your controller or when it gets thawed from the nib.

Singletons are useful, but I wouldn't resort to it unless you really need it. You can change your -applicationDidFinishLaunching to something like this:

- (void)applicationDidFinishLaunching:(UIApplication *)application {    

    //Set the values for the Variables and Constants, these are
    //accessed from the different classes.

    NSMutableDictionary *theHeart = [NSMutableDictionary dictionary];

    [theHeart setObject:[NSNumber numberWithInt:200] forKey:@"Money"];
    [theHeart setObject:@"Number two!" forKey:@"2"];

    [rootController setHeartDictionary:theHeart];

    [window addSubview:rootController.view];
    [window makeKeyAndVisible];
}

This assumes your rootController is of type OverviewController. Then in your OverviewController header you should declare a property like this:

@property (assign) NSMutableDictionary *heartDictionary;

and then @synthesize it in the .m file with @synthesize heartDictionary;.

Again, I wouldn't use a Singleton unless you need it. Pass it as a variable to your controller instead.