Sharing data between two classes

this is my first iPhone application and I'm using JSON framework to decode JSON sent from a server.

I insert the data in a NSMutableArray from an AppDelegate file.

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    

   responseData = [[NSMutableData data] retain];
   museums = [[NSMutableArray alloc] init];
   viewController = [[RootViewController alloc] init];
   NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://my_json_link"]];
   [[NSURLConnection alloc] initWithRequest:request delegate:self];

   [window addSubview:navigationController.view];
   [window makeKeyAndVisible];

   return YES;
}


- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
    [responseData setLength:0];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    [responseData appendData:data];
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    NSLog(@"Connection failed: %@", [error description]);
}


- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    [connection release];

    NSString *responseString = [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding];
    [responseData release];

    NSError *error;
    SBJSON *json = [[SBJSON new] autorelease];
    NSDictionary *data = (NSDictionary *)开发者_如何学Python[json objectWithString:responseString error:&error];
    [responseString release];   

    if (data == nil)
        NSLog(@"JSON parsing failed: %@", [error localizedDescription]);
    else {
        for (NSDictionary *item in data) {

            // Read the data 
            NSString *aName = [item objectForKey:@"name"];
            NSString *aDescription = [item objectForKey:@"description"];

            // Create a new museum object with the data from json 
            Museum *museum = [[Museum alloc] initWithName:aName description:aDescription];

            // Add the museum object to the Array
            [museums addObject:museum];
            [museum release];
        }       
    }   
    viewController.museums = museums;  
}

The museums array is not empty inside connectionDidFinishLoading function, but I can't see it when I try to print it in RootViewController. I tried to set the array in the line

viewController.museums = museums; 

but I didn't understand what is wrong.

I can fix the problem only if I move these lines:

[window addSubview:viewController.view];  
[window makeKeyAndVisible]; 

from the first function to connectionDidFinishLoading function. But in this case doesn't work the other view when I click one record of the table.

Thanks for any help.

viewController = [[RootViewController alloc] init];

First, I need you to make sure that the viewController you create in didFinishLaunching... is actually the correct viewController. Have you actually wired up that instance to be what you think it is or do you two instance os RootViewController?

Second if you are actually setting museums on the right instance of RootViewController you need to make sure that your timing is correct. This means that are you setting museums BEFORE you trying to print it out in viewController

--Edit--

OK since we established that things are happening in the wrong order you should try and reload the table. The UITableView has a method called reloadData that will take care of this for you and you need to call this everytime you change the data source after the table has been created.

So in RootViewController add a method called reload which in turn calls reloadData on your UITableView and modify your code:

viewController.museums = museums; 
[viewController reload];

You could add to your view controller, temporarily just for debugging:

-(void) setMuseums:(NSMutableArray*)m {
   self->_museums = [m retain];
}

and then add a breakpoint in there. Make sure it's getting hit, or maybe there's something later coming along and setting it to nil.

The Museums property is declared as @property (nonatomic, retain) NSMutableArray *museums; right?

Try to put a NSLog inside the for loop and check if it is executed.

try using

viewController.museums = [museums retain];