Ios – “Unrecognized selector sent to instance” error

iosobjective cuiviewcontroller

Part of my AppDelegate code is:

UITabBarController *tabBarController 
    = (UITabBarController *)self.window.rootViewController;

UINavigationController *navigationController 
    = [[tabBarController viewControllers] objectAtIndex:0];

PilotosViewController *playersViewController 
    = [[navigationController viewControllers] objectAtIndex:0];

playersViewController.drivers = players;

But I get this exception:

-[UIViewController viewControllers]: unrecognized selector sent to instance 0x6a75770
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[UIViewController
viewControllers]: unrecognized selector sent to instance 0x6a75770'

Where is the mistake?

Best Answer

I met the same issue, because I followed the steps by the author, but

UINavigationController *navigationController 
    = [[tabBarController viewControllers] objectAtIndex:0];

this is what which made the crash, because navigationController is not at index=0, I did exchange the locations of the two tab bar items, then it works.

Related Solutions

Objective-C: Calling selectors with multiple arguments

In Objective-C, a selector's signature consists of:

The name of the method (in this case it would be 'myTest') (required)
A ':' (colon) following the method name if the method has an input.
A name and ':' for every additional input.

Selectors have no knowledge of:

The input types
The method's return type.

Here's a class implementation where performMethodsViaSelectors method performs the other class methods by way of selectors:

@implementation ClassForSelectors
- (void) fooNoInputs {
    NSLog(@"Does nothing");
}
- (void) fooOneIput:(NSString*) first {
    NSLog(@"Logs %@", first);
}
- (void) fooFirstInput:(NSString*) first secondInput:(NSString*) second {
    NSLog(@"Logs %@ then %@", first, second);
}
- (void) performMethodsViaSelectors {
    [self performSelector:@selector(fooNoInputs)];
    [self performSelector:@selector(fooOneInput:) withObject:@"first"];
    [self performSelector:@selector(fooFirstInput:secondInput:) withObject:@"first" withObject:@"second"];
}
@end

The method you want to create a selector for has a single input, so you would create a selector for it like so:

SEL myTestSelector = @selector(myTest:);

Ios – Xcode – How to fix ‘NSUnknownKeyException’, reason: … this class is not key value coding-compliant for the key X” error

You may have a bad connection in your xib.

I've had this error many times. While TechZen's answer is absolutely right in this case, another common cause is when you change the name of a IBOutlet property in your .h/.m which you've already connected up to File's Owner in the nib.

From your nib:

Select the object in IB and go to the 'Connections Inspector'.
Under 'Referencing Outlets' make sure that your object isn't still connected to the old property name... if it is, click the small 'x' to delete the reference and build again.

Another common cause if you are using Storyboard, your UIButton might have more then one assignings (Solution is almost the same as for nib):

Open your storyboard and right click the UIButton
You will see that there is more than one assign/ref to this button. Remove one of the "Main..." greyed windows with the small "x":

Best Answer

Related Solutions

Objective-C: Calling selectors with multiple arguments

Ios – Xcode – How to fix ‘NSUnknownKeyException’, reason: … this class is not key value coding-compliant for the key X” error

You may have a bad connection in your xib.

Related Topic