我的JSONObjectWithData为null

Question

I have a problem with my JSON who send me a null value.

I think it's not a problem with my webservice in PhP because my colleague who is a expert in PhP doesn't see any error

Just below my Obj-C code

dispatch_queue_t downloadQueue = dispatch_queue_create("downloader", NULL);

        dispatch_async(downloadQueue, ^{
            NSData *result = self.envoyerLaDemande;
            dispatch_async(dispatch_get_main_queue(), ^{

                id strResult=nil;

                strResult = [NSJSONSerialization JSONObjectWithData:result options:0 error:nil];

                NSLog(@"strResult: %@", strResult);

                NSString* boolOk=[strResult objectForKey:@"result"];
                NSLog(@"BoolOk: %@", boolOk);

And there is the PHP script

$data = array();

if(condition == 1)
{
$data["result"] = "ok";
}
else
{
$data["result"] = "error";
}
$data["result"] = "coucou";
}
echo json_encode($data);

And the methode envoyerLaDemande

-(NSData*)envoyerLaDemande{


NSURL *url = [NSURL URLWithString:@"http://mywebsite.com.com/App/V2/mailTo.php"];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];

NSString* requestFields;


requestFields = [NSString stringWithFormat:@"agence=%@&", nomAgence];

request.HTTPBody = requestData;
request.HTTPMethod = @"POST";

NSHTTPURLResponse *response = nil;
NSError *error = nil;
NSData *responseData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];
if (error == nil && response.statusCode == 200) {
} else {
}
return responseData;

}

Answer 1

The problem is that you're doing two dispacth_async.

In the first one, you're telling the OS "Perform this code in the background", this will start loading the request in the background. However, immediately following that code you're telling the OS to perform a piece of code on the main thread. This piece of code accesses the result variable which hasn't been set yet because it's still being loaded in the background.

If you insist on using these dispatches, simply removing the dispatch back to the main queue should work. However, consider looking into NSURLConnectionDataDelegate or at the very least use the method sendAsynchronousRequest:queue:completionHandler on your NSURLConnection.

This code should work in your current scenario.

dispatch_queue_t downloadQueue = dispatch_queue_create("downloader", NULL);

dispatch_async(downloadQueue, ^{
    NSData *result = self.envoyerLaDemande;
    id strResult=nil;
    strResult = [NSJSONSerialization JSONObjectWithData:result options:0 error:nil];
    NSLog(@"strResult: %@", strResult);
    NSString* boolOk=[strResult objectForKey:@"result"];
    NSLog(@"BoolOk: %@", boolOk);
}

EDIT:

Instead of simply ignoring the error and response objects, use them to diagnose the problem:

NSHTTPURLResponse *response = nil;
NSError *error = nil;
NSData *responseData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];
if (error == nil && response.statusCode == 200) {
    return responseData;
} else {
    NSLog(@"Error. Status code: %d Error message: %@", response.statusCode, error.localizedDescription);
    return nil;
}