Question

On the server side, I have code like this to provide JSON to my iOS application:

      $val = array("a", "b", "c","d");
      return json_encode($val);

Within that application, I try to communicate with the server using the following code:

NSError *error = nil;

NSString *szURL =@"http://192.168.1.159/return.php";

NSURL *url = [NSURL URLWithString:szURL];

NSString *strData = [NSString stringWithContentsOfURL:url
                                             encoding:NSUTF8StringEncoding
                                                error:&error];

NSArray *appLists = (NSArray *)[strData JSONValue];

However, strData is always nil. Why is this happening, and what can I do to prevent it?

Answer 1

I would recommend, unless you want your requests to occur synchronously and block up the UI, to perform an asynchronous request using NSURLConnection or a third party solution. I like TTURLRequest from http://three20.info because it makes it very easy to specify headers, gets the JSON value from the data, etc. An example call would look like this:

TTURLRequest *request = [[TTURLRequest alloc] initWithURL:@"http://192.168.1.159/return.php" delegate:self];
request.httpMethod = @"GET";
request.response = [[[TTURLJSONResponse alloc] init] autorelease];
request.cachePolicy = TTURLRequestCachePolicyNone;
[request send];

Then your delegate must implement these methods:

-(void)requestDidFinishLoad:(TTURLRequest *)request;
-(void)request:(TTURLRequest *)request didFailLoadWithError:(NSError *)error;