Question

I am practicing delegate in iphone development but have a problem

2012-05-12 21:21:54.279 DelegatePractice[2924:f803] -[secondViewController viewControllers]: unrecognized selector sent to instance 0x6b61d10
2012-05-12 21:21:54.281 DelegatePractice[2924:f803] * Terminating app due to uncaught exception ‘NSInvalidArgumentException’, reason: ‘-[secondViewController viewControllers]: unrecognized selector sent to instance 0x6b61d10’
* First throw call stack:
(0x13bb052 0x154cd0a 0x13bcced 0x1321f00 0x1321ce2 0x2596 0x436e1e 0x13bcec9 0x155c2 0x250d54 0x13bcec9 0x155c2 0x1555a 0xbab76 0xbb03f 0xba2fe 0x3aa30 0x3ac56 0x21384 0x14aa9 0x12a5fa9 0x138f1c5 0x12f4022 0x12f290a 0x12f1db4 0x12f1ccb 0x12a4879 0x12a493e 0x12a9b 0x1e98 0x1df5)

and I think I set up the delegate properly:

delegateViewController.m

- (void)secondViewControllerDidJump:
(secondViewController *)controller
{
    [self dismissViewControllerAnimated:YES completion:nil];
}

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    if ([segue.identifier isEqualToString:@"jump"])
    {
        UINavigationController *navigationController = segue.destinationViewController;
        secondViewController *SecondViewController =[[navigationController viewControllers]objectAtIndex:0];
        SecondViewController.delegate = self;
    }
}

@end

secondViewController.h

@class secondViewController;

@protocol SecondViewControllerDelegate <NSObject>
- (void)secondViewControllerDidJump: (secondViewController *)controller;

@end

@interface secondViewController : UITableViewController

@property (strong,nonatomic) NSArray *choices;
@property (nonatomic, weak) id <SecondViewControllerDelegate> delegate;

- (IBAction)jump:(id)sender;

@end

secondViewController.m

- (IBAction)jump:(id)sender
{
    [self.delegate secondViewControllerDidJump:self];
}

Answer 1

Your app crashes in these lines:

UINavigationController *navigationController = segue.destinationViewController;
secondViewController *SecondViewController =[[navigationController viewControllers]objectAtIndex:0];

You ask navigationController for its viewControllers, but the log makes clear that navigationController is not a UINavigationController but a secondViewController, which does not respond to the selector -viewControllers.

Make sure that segue.destinationViewController really returns a UINavigationController.