Question

I have 2 classes. A and B. Inside ClassA I have a method which retrieve JSON data and adds into an array. I want to access this array from ClassB. How can I achieve it?

ClassA.h
- (void)viewDidLoad
{
//initialise arrayPlaces and arrayWeather
[super viewDidLoad];

dispatch_async(queue, ^{
NSData* data = [NSData dataWithContentsOfURL: 
                    serverURL];
                    [self performSelectorOnMainThread:@selector(fetchedData:) 
                    withObject:data waitUntilDone:YES];
});
}

- (void)fetchedData:(NSData *)responseData {

//parse out the json data
NSError *error;
NSMutableArray *tempArray = [[NSMutableArray alloc] init];
tempArray = [NSJSONSerialization 
             JSONObjectWithData:responseData //1
             options:kNilOptions 
             error:&error];

//declare arrayPlaces
arrayToPass = [[NSMutableArray alloc] init];

//...codes to add array here using a loop...
[arrayToPass addObject:tempString];
}

In ClassB, I have a tableView which i want to get all the array from ClassA. How can I achieve this?

ClassA *cA = [[ClassA alloc]init];
ClassA.view;
arrayReceived = ClassA.arrayToPass;

The above doesn’t seem to work when implemented in ClassB.

ClassB *cB = [[ClassB alloc] init];
[cB setArrayReceived:arrayToPass];

Neither does this work when implemented in ClassA after this portion of the code.
“//…codes to add array here using a loop…
[arrayToPass addObject:tempString];

Please help!! Thanks!

Answer 1

The reason your code does not work is because fetchData: is done asynchronously and arrayToPass is still not populated when the code arrayReceived = ClassA.arrayToPass; runs.

So we have to let ClassB know about that.
How about first declaring a protocol ClassADelegate between ClassA and ClassB, and declare a property in ClassA that of type ClassADelegate like this:

in ClassA.h
@protocol ClassADelegate ;//Forward declaration of the protocol
@interface ClassA {...
}
@property (nonatomic, assign) id <ClassADelegate> delegate;
@end

@protocol ClassADelegate <NSObject> 
-(void) classADidReceiveData:(NSArray *)array;
@end

then make ClassB a delegate of this

@interface ClassB : <ClassADelegate> { ...

and of course implement the method classADidReceiveData: in ClassB:

-(void)classADidReceiveData:(NSArray*) array{
 arrayReceived = array;
}

Then modify fetchData: like:

- (void)fetchedData:(NSData *)responseData {

...
//...codes to add array here using a loop...
[arrayToPass addObject:tempString];

 //Call the delegate method if a delegate has been set
if(delegate){
     [delegate classADidReceiveData:arrayToPass]
}
}

So that when ClassA received data, it can make ClassB noticed about that.

The overall usage is:

ClassA *cA = [[ClassA alloc]init];
cA.delegate = self;
cA.view;

If you have something to be done after fetching data in ClassB, then do it in classADidReceiveData in ClassB.

-(void)classADidReceiveData:(NSArray *)array{
 arrayReceived = array;
 //Do whatever you want after receiving array
}