Updating an Arrays content who's method uses if(myArray ==nil) to check prior to first build.

Hi Stephen,

you might want to consider the use of NSMutableArray instead of NSArray as IMHO this seems to make more sense for the purpose you just described (at least if I got that right :) ).

Kind Regards Holger

Are you using the MVC Model? Are you then persisting your Model in some way (e.g. DB, plist... ) and if so, how do you do it and why?

I'm sorry, Stephen, but at this very moment I don't fully understand what you're doing with your App or planning to do, the structure and exactly why and how you're using many NSMutableArray's. Why do you have to check if a certain NSMutableArray is empty?

Without knowing the details of your project I would recommend using a property for checking/conserving the status of something like:

@property (nonatomic, assign) BOOL statusArray;

...

somewhere in your code:
statusArray = YES;

...

if (statusA) {
   do something if statusArray = true;
} else {
   do something if statusArray = false;
};

The approach described in the Crystal Ball app is for a static set of items. If you want to create a model object that can adapt based on the data being passed then as Holger mentioned you need to use a NSMutableArray. Let's say you have a class called SalesData. This class can contain public methods like: addData, removeData and data . In the implementation you you add and remove data to your array but you never directly provide public access to the array.

Here's an example (warning: source code has not been compiled so might contain syntax errors):

// Interface Definition
// SalesData.h

@interface SalesData : NSObject 

- (void) addData:(id)data;
- (void) removeData:(id)data;
- (NSArray*) data;
@end


// Implementation
// SalesData.m

// Class extension in the .m file to create a private property
@interface SalesData ()
@property (nonatomic, strong) NSMutableArray *items;
@end

@implementation SalesData

- (NSMutableArray*) items {
    if ( !_items ) {
         _items = [NSMutableArray array];
        // add other items here if you need to initialize it with some data.
    }
   return _items;
}

- (void) addData:(id)data {
    [self.items addObject:data];
}
- (void) removeData:(id)data {
    [self.items removeObject:data];
}

- (NSArray*) data {
    return self.items;
}


@end

Hope that answers your question.