ios — как извлечь данные из php-файла в цель C

Я застрял на этой проблеме некоторое время, поэтому я был бы очень признателен за помощь. Я очень новичок в программировании приложений для iOS. Я начал с приложения входа в систему, но я столкнулся с некоторой проблемой в получении «статуса входа в систему успешно» при получении ответа из файла php. Я просто получаю «Ошибка входа». Я собираюсь дать вам мой код. Пожалуйста, исправьте мою ошибку.
(ViewController.m) код файла //

    #import "ViewController.h"#import "SBJson.h"@interface ViewController ()

@end

@implementation ViewController

-(void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
}

- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
-(IBAction)signinclicked:(id)sender
{

NSInteger success=0;
@try {

if([[self.txtusername text] isEqualToString:@""] || [[self.txtpassword text]                 isEqualToString:@""] ) {

[self alertStatus:@"Please enter Email and Password" :@"Sign in Failed!" :0];} else {

NSString *post =[[NSString  alloc]initWithFormat:@"username=%@ & password=%@",         [self.txtusername text],[self.txtpassword text]];
NSLog(@"PostData: %@",post);

NSURL *url=[NSURL URLWithString:@"http://shiv.9gem.net/alka/index1.php"];

NSData *postData = [post dataUsingEncoding:NSASCIIStringEncoding    allowLossyConversion:YES];

NSString *postLength = [NSString stringWithFormat:@"%lu", (unsigned long)                    [postData length]];

NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
[request setURL:url];
[request setHTTPMethod:@"POST"];
[request setValue:postLength forHTTPHeaderField:@"Content-Length"];
[request setValue:@"application/json" forHTTPHeaderField:@"Accept"];
[request setValue:@"application/x-www-form-urlencoded"                        forHTTPHeaderField:@"Content-Type"];
[request setHTTPBody:postData];

//[NSURLRequest setAllowsAnyHTTPSCertificate:YES forHost:[url host]];

NSError *error = [[NSError alloc] init];
NSHTTPURLResponse *response = nil;
NSData *urlData=[NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];

NSLog(@"Response code: %ld", (long)[response statusCode]);

if ([response statusCode] >= 200 && [response statusCode] < 300)
{
NSString *responseData = [[NSString alloc]initWithData:urlData encoding:NSUTF8StringEncoding];
NSLog(@"Response ==> %@", responseData);NSError *error = nil;
NSDictionary *jsonData = [NSJSONSerialization
JSONObjectWithData:urlData
options:NSJSONReadingMutableContainers
error:&error];

success = [jsonData[@"success"] integerValue];
NSLog(@"Success: %ld",(long)success);

if(success == 1)
{
NSLog(@"Login SUCCESS");
} else {

NSString *error_msg = (NSString *) jsonData[@"error_message"];
[self alertStatus:error_msg :@"Sign in Failed!" :0];
}

} else {
//if (error) NSLog(@"Error: %@", error);
[self alertStatus:@"Connection Failed" :@"Sign in Failed!" :0];
}
}
}
@catch (NSException * e) {
NSLog(@"Exception: %@", e);
[self alertStatus:@"Sign in Failed." :@"Error!" :0];
}
if (success) {
[self performSegueWithIdentifier:@"login_success" sender:self];
}
}

- (void) alertStatus:(NSString *)msg :(NSString *)title :(int) tag
{
UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:title
message:msg
delegate:self
cancelButtonTitle:@"Ok"otherButtonTitles:nil, nil];
alertView.tag = tag;
[alertView show];
}
- (IBAction)backgroundtap:(id)sender {
[self.view endEditing:YES];
}
-(BOOL)textFieldShouldReturn:(UITextField *)textField{
[textField resignFirstResponder];
return YES;
}

@end

***( php file code)***<?php
header('content-type:application/json');
$dbhost = 'localhost';

$dbuser = 'shiv9gem_alka';

$dbpass = 'alankritasharma';

$conn = mysql_connect($dbhost, $dbuser, $dbpass);

if(!$conn )

{

die('Could not connect: ' . mysql_error());

}

$sql = 'SELECT username,password FROM student';mysql_select_db('shiv9gem_project');

$retval = mysql_query( $sql, $conn );

if(! $retval )

{

die('Could not get data: ' . mysql_error());

}

while($row = mysql_fetch_array($retval, MYSQL_ASSOC))

{echo json_encode($row);
}

echo "Fetched data successfully\n";if($_POST)
{
if($_POST['username']=='alankrita' && $_POST['password']=='isha123')
{
echo '{"success":1}';
}
else
{
echo '{"success":0,"error_message":"username and/or password is invalid."}';
}
} else
{
echo '{"success":0,"error_message":"username and/or password is invalid."}'; }
mysql_close($conn);?>