iPhone App - JSONKit objectFromJSONString returns null

Hi I have an iPhone app that uses ASIFormDataRequest to post a variable to a php file. The php file then returns a set of tuples from my remote database in the form of an associative array.

I use objectFromJSONString to deserialise the json data (using the JSONKit framework), but pon printing out the data, I get null. Here is my code:

+(NSDictionary*)getQuestions:(NSString*)sectionId from: (NSString*) url{
    NSDictionary *questions;
    NSURL *link = [NSURL URLWithString:url];
    ASIFormDataRequest *request = [ASIFormDataRequest requestWithURL:link];
    [request setPostValue:sectionId forKey:@"section"];
    NSError *error = [request error];
    [request setDelegate:self];
[request setDidFinishSelector:@selector(requestFinished:)];
    [request startAsynchronous];

    if (!error) {       
        //NSString *response = [request responseString];
        //store them in the dictionary
        NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:url]];
        NSString *json = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
        questions = [json objectFromJSONString];    
        NSLog(@"%@",questions); //prints null
        [json release];
        [request release];      
    }else{
        //UIAlertView to warn users there was an error
    }               

    return questions;   
}

//doesn't work
- (void)requestFinished:(ASIHTTPRequest *)request
{
    //NSString *response = [request responseString];
    NSLog(@"hello"); //never prints
}

@end

@implementation dbQuestionGetterViewController
@synthesize questions;

-(void)viewDidLoad{
    //code to initialise view
    NSDictionary* arr = [dbConnector getQuestions:@"2" from:@"http://dev.speechlink.co.uk/David/get_questions.php"];
    self.questions = arr;
    [super viewDidLoad];
}
@end

I have tried using an ASIHTTPRequest calback delegate (didFinishSelector)

UPDATE:

Here is the link to the php. When you click it you can see it's outputting JSON properly:

http://dev.speechlink.co.uk/David/get_questionstest.php

Here is the php:

<?php

//connect to database

$dbh = mysql_connect ("localhost", "abc", "123") or die ('I cannot connect to the database because: ' . mysql_error());
mysql_select_db("PDS", $dbh); 

$query = mysql_query("SELECT * FROM Questions WHERE sectionId = 1") or die("Error: " . mysql_erro开发者_StackOverflow中文版r());;

$rows = array();
while($r = mysql_fetch_assoc($query)) {
  $rows[] = $r;
}
//echo '{"questions":'.json_encode($rows).'}';
echo json_encode($rows);
mysql_close();

?>

---

It will return nil if the string you're passing in isn't valid JSON.

There's two things that might be happening :

(1) You're not parsing the server's response properly - try outputting the json string to see what you think it is i.e.

NSString *json = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
NSLog(@"%@", json);

(2) The server is not sending correct JSON - try opening the URL in a browser and making sure that it's correctly formed.