Question

I have a doubt regarding downloading data from a web service. One way is to download it in a single line mentioned below.

NSString *returnString = [[NSString alloc] initWithData:[NSURLConnection sendSynchronousRequest:urlrequest returningResponse:nil error:nil] encoding:NSUTF8StringEncoding];

And the other way to get it is via connectionDidFinishLoading

    [..]
    NSURLConnection *theConnection = [[NSURLConnection alloc] initWithRequest:urlrequest delegate:self];  

    NSHTTPURLResponse *response;  
   [NSURLConnection sendSynchronousRequest: urlrequest returningResponse: &response error: nil];   

    if( theConnection )  
    {  
        webData = [[NSMutableData data] retain];  
    }  
    else  
    {  
        NSLog(@"theConnection is NULL");  
    }  

}  

-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{   
    [webData setLength: 0];  
}  
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data  
{  
    [webData appendData:data];  
}  
-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{  
    NSLog(@"ERROR with theConenction");  
    [connection release];  
    [webData release];  
}  
-(void)connectionDidFinishLoading:(NSURLConnection *)connection
{  
    NSLog(@"DONE. Received Bytes: %d", [webData length]);  
    NSString *theXML = [[NSString alloc] initWithBytes: [webData mutableBytes] length:  [webData length] encoding:NSUTF8StringEncoding];  
}

Is there any difference between these two? NSURLConnection delegate method is not called when I use a separate class to parse the response.

Answer 1

You’re using sendSynchronousRequest:returningResponse:error: which does not call any delegates methods because it doesn’t need to: when you call it, the main thread stops until the request is finished and you get the response.

If you want to make an asynchronous request, use connectionWithRequest:delegate:. I recommend to always do asynchronous responses since the synchronous request blocks the main thread and your UI can’t respond during that time. Animations will become interrupted. Scrolling becomes jerky. If you do want to use synchronous requests you should do it in a background thread.