Code keeps crashing with passing data - ios

Question

I'm building my first iOS app with a login system. I've built some simple things before, but this is on a whole new level. Currently I'm able to login and get some data back from the server. The app then performs a model segue to MainView with MainController attached to it.
When I log in, the app gets token and success back from the server. This token is needed for further requests to the server. However, I can't seem to figure out how to pass the token to MainController. It doesn't matter what I try, the app crashes with an unknown error.
Right now - with the code below - it throws:
2014-10-11 14:30:14.077 LoginScreen[29076:4688502] -[UINavigationController setXAuthToken:]: unrecognized selector sent to instance 0x7bfd1140
2014-10-11 14:30:14.104 LoginScreen[29076:4688502] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[UINavigationController setXAuthToken:]: unrecognized selector sent to instance 0x7bfd1140'
ViewController.h
#import <UIKit/UIKit.h>
#import "MainController.h"
#interface ViewController : UIViewController <UITextFieldDelegate>
#property (weak, nonatomic) IBOutlet UITextField *txtUsername;
#property (weak, nonatomic) IBOutlet UITextField *txtPassword;
- (IBAction)sigininClicked:(id)sender;
- (IBAction)backgroundTap:(id)sender;
#end
ViewController.m
#import "ViewController.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)sigininClicked:(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://www.mywebsite.com/auth"];
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)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if ([segue.identifier isEqualToString:#"login_success"]) {
MainController *controller = (MainController *)segue.destinationViewController;
controller.xAuthToken = #"test string";
}
}
- (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
MainController.h
#import <Foundation/Foundation.h>
#interface MainController : UIViewController
#property (nonatomic,strong) NSString *xAuthToken;
#end
MainController.m
#import "MainController.h"
#interface MainController ()
#end
#implementation MainController
- (void)viewDidLoad
{
NSLog(#"%#",_xAuthToken);
}
#end

Answer 1

The stack trace tells you what the problem is - you are trying to set the XAuthToken property on a UINavigationController - but a UINavigationController doesn't have that property.
Your MainController instance is embedded in a UINavigationController, so that is what you get from destinationViewController in prepareForSegue.
You need to access the view controller stack -
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if ([segue.identifier isEqualToString:#"login_success"]) {
UINavigationController *navController = (UINavigationController *)segue.destinationViewController;
MainController *controller = (MainController *)navController.topViewController
controller.xAuthToken = #"test string";
}
}