why nsurldelegates method are not called when json parsing in iphone

I am developing one iphone application from google places API. For that I am doing JSON parsing for getting data.

For JSON parsing I have made one class and in which I'm writting these methods in JsonParse.m file following methods are written:

- (void)initWithURLString:(NSString *)aURLString parameter:(UIViewController *)viewController
{

    NSURL *url = [NSURL URLWithString:aURLString];
        NSMutableURL开发者_开发问答Request *request = [NSMutableURLRequest requestWithURL:url];
    connection=[[NSURLConnection alloc] initWithRequest:request delegate:viewController];

}

-(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
{
    label.text=[NSString stringWithFormat:@"error in the connection %@",[error    description]];
}

-(void)connectionDidFinishLoading:(NSURLConnection *)connection
{
   NSString *responsestring=[[NSString alloc] initWithData:responseData  encoding:NSUTF8StringEncoding];

    NSLog(@"response string is %@",responsestring);

    NSError *error;
    SBJSON *json=[[SBJSON new]autorelease];
    NSMutableDictionary *response=[NSMutableDictionary dictionary];
    response=[json objectWithString:responsestring  error:&error];

    NSLog(@"values in the dictionary is %@",[response valueForKey:@"results"]);         
} 

And I am calling the method from the viewcontroller class as below:

JsonParse *obj=[[JsonParse alloc] init];
[obj initWithURLString:urlstr parameter:self];

But when I am debugging only initwithurl method is called, other connection delegate methods are not called.

Previously I have written the methods in the same class means in the viewcontroller class at that time every method was called and I was able to prase data.

I have written this method in seperate class because in the same viewcontroller class I want to parse data multiple times (more that 1 time with different urls).

Does anyone know why these methods are not called or how can I parse multiple times in the same class? Any tutorial or sample code for that?

In :

// the delegate must be self
connection=[[NSURLConnection alloc] initWithRequest:request
                                           delegate:viewController];

The delegate should be self in order for these methods to get called, because these methods are implemented in JsonParse.