iPhone xcode array losing state after load

Question

Right i've had a search around and can't find anything.

@synthesize list; // this is an NSArry

-(void) viewDidLoad {
   NSArray *arr = [self getJSONFeed];
   self.List = [arr retain];     // if i copy the access code into here it works fine.
}

-(void) tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    NSUInteger row = [indexPath row];
    NSArray *vals = [list objectAtIndex:row] retain];
    NSString *id = [vals valueForKey:@"id"]; // ERROR
}

Right i've taken some of the code to try and provide it as simple as possible, ignore typo's and memory leaks this is sorted.

Basically when I select a row I can't get data out of my 'list' array object. Please can anyone help me out?

---

This is my full code

I'm using http://code.google.com/p/json-framework/ for my JSON connection

my Json is returned in this format:

[
    {
        "id": "7812",
        "title": "title1",
        "fulltext": "main body text",
        "created": "2010-04-06 11:30:03"
    },
    {
        "id": "7813",
        "title": "title2",
        "fulltext": "main body text2",
        "created": "2010-04-06 11:30:03"
    }
]

MainNewsController.h

in here declare:

NSArray *list:   
@property (nonatomic, retain) NSArray *list;

MainNewsController.m

@synthesize list;

-(void) viewDidLoad {
    NSArray *array =  [[NSArray alloc] initWithArray: [self downloadPublicJaikuFeed]];
    self.list = array;    
    NSArray *stream = [list objectAtIndex:6]; // can change index and it's fine
    NSString *vall = [stream valueForKey:@"title"]; // works fine    
    NSString *val1l = [stream valueForKey:@"id"]; // works fine
}

-(NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return [self.list count];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *MainNewsCellIdentifier = @"MainNewsCellIdentifier";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier: MainNewsCellIdentifier];    
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier: MainNewsCellIdentifier] autorelease];
    }
    NSUInteger row = [indexPath row];
    NSDictionary *stream = (NSDictionary *) [list objectAtIndex:row];
    cell.textLabel.text = [stream valueForKey:@"id"];
    cell.accessoryType = UITableViewCellAccessoryDetailDisclosureButton;
    [stream release];
    return cell;
}

#pragma mark -    
#pragma mark Table Delegate Methods

- (void) tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    if (childController == nil)    
        childController = [[MainNewsDetailController alloc] initWithNibName:@"DisclosureDetail" bundle:nil];
    childController.title = @"News Detail Button Pressed";    
    NSUInteger row = [indexPath row];
    NSArray *stream = (NSArray *) [self.list objectAtIndex:row];
    NSString *vall = [stream valueForKey:@"title"]; // error
    NSString *val1l = [stream valueForKey:@"id"]; // error
    childController.message = @"111";
    childController.title = @"222";
    [self.navigationController pushViewController:childController animated:YES];
}

Answer 1

Maybe you should try the following (create a temporary array, pass this to the property method and release it afterwards):

 NSArray *arr = [[NSArray alloc] initWithArray:[self getJSONFeed]];
 self.list = arr;
 [arr release];

Make sure you set the property for your NSArray list with (nonatomic, retain) or (nonatomic, copy). Also you have to release the NSArray list in the dealloc method of this class.

Answer 2

Seems like you try to read objects from an array using key-value coding, which will not work (at least it won't do what you expect). If the object you get at that position is really an array, you need to access the elements with objectAtIndex:.

Try setting a breakpoint at the line NSString *id = [vals valueForKey:@"id"]; and inspect vals to see if this object is and contains what you expect.

Answer 3

I doubt vals is an array. Based on the example you've shown as JSON exmaple, it should be a dictionary.

NSDictionary *vals = [list objectAtIndex:row];

Also, you don't need to use retain, for a variable that is allocated and used only inside the scope;

And Why don't you use:

NSString *id = [vals objectForKey:@"id"];

To get something from a dictionary object, you use objectForKey, not valueForKey. valueForKey is used for other purposes related to transforming the object for other use

Answer 4

Also, note that JSON will come back as different structures sometimes if there are less elements than you expect. For example, if there were two dictionaries that come back, you might get an array, but if only one, it is just the straight key/value structure (dictionary). I've seen in cases where zero results are returned it can return an empty string ("").