iOS 5 JSON to tableView error - objective-c

Question

I was trying to parse a JSON string from USGS. However I get error "-[__NSCFDictionary objectAtIndex:]: unrecognized selector sent to instance 0x68a34c0" Basically, I would like to parse the USGS JSON into the tableview. Can anyone help? Here are my codes.
ViewController.h
#interface EarthquakeViewController : UITableViewController
{
NSArray *json;
NSDictionary *earthquakeReport;
}
ViewController.m
- (void)viewDidLoad
{
//content = [NSMutableArray arrayWithObjects:#"one", #"two", nil];
[super viewDidLoad];
[self fetchReports];
}
- (void)fetchReports
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSData* data = [NSData dataWithContentsOfURL:
[NSURL URLWithString: #"http://earthquake.usgs.gov/earthquakes/feed/geojson/all/hour"]];
NSError* error;
json = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments error:&error];
NSLog(#"%#", json);
dispatch_async(dispatch_get_main_queue(), ^{
[self.tableView reloadData];
});
});
}
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
// Return the number of sections.
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
// Return the number of rows in the section.
return json.count;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
}
earthquakeReport = [json objectAtIndex:indexPath.row];
NSString *country = [[[earthquakeReport objectForKey:#"features"] objectForKey:#"properties"] objectForKey:#"place"];
NSString *mag = [[[earthquakeReport objectForKey:#"features"] objectForKey:#"properties"] objectForKey:#"mag"];
cell.textLabel.text = country;
cell.detailTextLabel.text = mag;
return cell;
}
The error is showing at the line earthquakeReport = [json objectAtIndex:indexPath.row];

Answer 1

If you look at your JSON data in a web browser (http://earthquake.usgs.gov/earthquakes/feed/geojson/all/hour) you should notice that the array you are trying to access is not at the root level. The root level is a dictionary, and the array you're looking for is in the "features" key.
To access it properly, first change your json ivar declaration into an NSDictionary:
NSDictionary *json;
Then, in your tableView:cellForRowAtIndexPath: method, access the report thusly:
earthquakeReport = [[json objectForKey:#"features"] objectAtIndex:indexPath.row];