How do I debug an 'unrecognized selector sent to instance' problem?

Question

I have the following code in a view controller that (in all other respects) seems to be working fine:

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    ProblemViewController *problemViewController = [[ProblemViewController alloc] initWithNibName:@"ProblemViewController" bundle:nil];
    problemViewController.problem = (Problem*)[self.problems objectAtIndex:indexPath.row];
    [self.navigationController pushViewController:problemViewController];
    [problemViewController release];
}

When I run through this function, however, I am getting the following error:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[ProblemViewController initWithNibName:bundle:]: unrecognized selector sent to instance 0x57ca80'

I'm at a loss as to what could be causing it, so my question is: How should I best go about debugging this problem? Is there anything obvious I should be checking?

Answer 1

Check the base class for ProblemViewController. I'm betting you're not inheriting from UIViewController, which includes the initWithNibName:bundle: method.

Answer 2

There are a bunch of answers to this question that all basically say the same, correct, thing: Somehow, the method you're trying to call doesn't actually exist.

BUT, if you're beating your head against the wall (like I was for an hour today), make sure you try cleaning your project in xcode first. Sometimes, I don't know why, xcode can get into a bad state and will not properly compile your project into the simulator. It will tell you the build is successful, but when deployed to the simulator, you start seeing runtime errors as though only half your changes were picked up. So yeah, that happens.

Answer 3

You likely don't have that method implemented in your ProblemViewController. Unrecognized selector is, as far as I know, just that there's no method defined in this class's interface that has that signature.

Try declaring it in your interface like this:

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil;

Answer 4

I thought I better post something on this issue. I fought it for a couple of days. There are a lot of blogs on this, but none of them solved the problem. Some suggested that it had to do with pushViewController needing to specify animated:YES. It worked for some, but that didn't work for the issue I was having. I was using a button to access another view rather than selecting a row from a table view, but was getting the same unrecognized selector error. I was also using a navigation controller so I thought it had something to do with that, but it didn't. Finally, I decided to comment out lines of code till the message went away. After commenting out the method that was causing the problem, the error message still came up in the console. That is when I realized the problem was not with my source code. One site recommended performing a clean and rebuild. I tried all that and still the problem persisted. I then looked at my XIB file using Interface Builder to see what methods(Received Actions) displayed on the File Owner. There was the problem. Not only did the offending method show up once on the File Owner, but it displayed twice. Don't know how to display the image of this here. Anyway, I deleted the methods (Received Actions) with the same name that appeared on the File Owner. I performed a clean and rebuild to see if the error went away and it did. I then uncommented the source I thought was bad and built the project again and the call to the new view was successful.