iOS: trouble sharing data between two view controllers - iphone

Question

I have an app, which has a first view controller called MainViewController that's sorta like a stopwatch, and when I click finish, it displays a UIAlertView pushes another view controller, EndViewController, which shows how long the stopwatch was running and how long it was paused. I am getting the following errors:
My Point[851:c07] -[EndViewController topViewController]: unrecognized selector sent to instance 0x754db60
My Point[851:c07] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[EndViewController topViewController]: unrecognized selector sent to instance 0x754db60'
Can anyone point ou to me what's wrong?
heres my code:
MainViewController.h:
#import "EndViewController.h"
#interface MainViewController : UIViewController <UITableViewDataSource, UITableViewDelegate, UITextFieldDelegate, UIAlertViewDelegate>
#property (strong, nonatomic) IBOutlet UILabel *out;
#property (strong, nonatomic) IBOutlet UILabel *in;
#end
MainViewController.m:
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{
if ([segue.identifier isEqualToString:#"endtask"]){
UINavigationController *navController = (UINavigationController *)segue.destinationViewController;
EndViewController *controller = (EndViewController *)navController.topViewController;
controller.timeIn.text=_in.text;
}
}
- (void)viewDidLoad
{
[super viewDidLoad];
_alert = [[UIAlertView alloc] initWithTitle:#"Are you sure?"
message:nil
delegate:self
cancelButtonTitle:#"NO"
otherButtonTitles:#"YES", nil];
}
- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{
if (buttonIndex == 0) {
//do nothing
}
else if (buttonIndex == 1) {
[self performSegueWithIdentifier:#"endtask" sender:self];
}}
- (IBAction)endButton:(UIButton *)sender {
[_alert show];
}
- (IBAction)endButton:(UIButton *)sender {
[_alert show];
}
EndViewController.h:
#interface EndViewController : UIViewController
#property (weak, nonatomic) IBOutlet UILabel *timeIn;
#end

Answer 1

You're calling a method named topViewController on an object which doesn't have the method/property. It's this line here:
EndViewController *controller = (EndViewController *)navController.topViewController;
I would suspect its because the view controller you are assigning to navController isn't actually a navigation controller, but is something else. Check your storyboards/nibs for this.
Also, try logging navController, as one commentor said, and see what that gives you.
NSLog(#"%#", navController);

Answer 2

If you are passing a string with timeIn you should have #property of a NSString in the endViewController.h
#property (strong, nonatomic) NSString * timeIn ;
Then in you endViewController.m you put the timeIn into a labe for example.
myLabel.text = timeIn;