NSURLSession post -- NSURLSessionDataTask

<pre name="code" class="objc">- (IBAction)onRegisterBtnClick:(UIButton *)sender {
NSLog(@"start to register.");
NSString *registerUrl = [[FJConstantsUtil remoteServerUrl] stringByAppendingString:[FJConstantsUtil registerPath]];
NSURL *url = [NSURL URLWithString:registerUrl];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
request.HTTPMethod = @"POST";

NSString *account = self.accountField.text;
NSString *nickname = self.nicknameField.text;
NSString *password = self.passwordField.text;
NSDictionary *parameterDict = @{
@"account" : account,
@"nickname": nickname,
@"password": password
};
NSData *data = [NSJSONSerialization dataWithJSONObject:parameterDict options:NSJSONWritingPrettyPrinted error:nil];
request.HTTPBody = data;

[request setValue:@"application/json" forHTTPHeaderField:@"Content-Type"];

NSURLSession *session = [NSURLSession sharedSession];
NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
NSLog(@"dataTask ends.");
if (data == nil || error)
return;
NSDictionary *dict = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableLeaves error:nil];
NSInteger resultUserid = dict[@"userid"];
}];

[dataTask resume];
}