Unrecognised selector on button press

Question

I can't believe i'm stumbling on something so simple:

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {

        UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
        [button setTitle:@"Tap me" forState:UIControlStateNormal];
        [button addTarget:self action:@selector(test) forControlEvents:UIControlEventTouchUpInside];

        button.frame = CGRectMake(50, 50, 120, 60);
        [self.view addSubview:button];

    }
    return self;
}

-(void)test {
    NSLog(@"Test");
}

It crashes when I press the button, with an unrecognized selector sent to instance error.

Anybody know what I could be doing wrong here?

Edit - error message:

-[__NSCFString test]: unrecognized selector sent to instance 0x29ee30
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFString test]: unrecognized selector sent to instance 0x29ee30'

Edit - how it's presented (ARC):

DemoViewController *demoVC = [[DemoViewController alloc] init];
    [self.window addSubview:demoVC.view];

    [self.window makeKeyAndVisible];

are you sure that you are recieving "unrecognized selector sent to instance" and not another exception? — Omar Abdelhafith, Jul 01 '12 at 19:20
Yes, it's declared there, although that shouldn't make a difference. — Andrew, Jul 01 '12 at 19:22
@WendiKidd - it doesn't matter if it's declared or not. Obj-C is a dynamic language, the declarations are just for fooling the compiler. If the method is **implemented**, the runtime **does** recognize the selector. — , Jul 01 '12 at 19:22
Btw, are you sure you implemented `-test` and not `-test:` or the other way around? — , Jul 01 '12 at 19:23
Hmm, could it be a retain issue on the button object or its container then? /ponders — WendiKidd, Jul 01 '12 at 19:24

score 10 · Accepted Answer · answered Jul 01 '12 at 19:29

If you are using ARC, then demoVC.view will be realeasd just after the function ends, instead of just initializing like this

DemoViewController *demoVC = [[DemoViewController alloc] init];

Make a strong property around demoVC and initialize it as this

self.demoVC = [[DemoViewController alloc] init];

score 3 · Answer 2 · edited May 23 '17 at 12:04

Your error message indicates (most likely) that your view controller is being deallocated before the button is pushed. (It shows that the message is being sent to an NSString, which is probably occupying the memory that the view controller used to be at.)

The easiest way to hunt this down is to use zombies to confirm this and identify why your object is being deallocated early.

EDIT: Based on your presentation code, you should make, for example, an instance variable to keep a reference to your view controller. You probably also want to move your button initialization code to viewDidLoad to avoid other problems in the future. (Or just hook up the button in a nib!)

Luavis · Answer 3 · 2012-07-01T23:07:36.823

-1

when adding any UI Component with code it need to add in viewDidLoad or loadView(if you don`t add xib file) override method.

and also you need to add parameter for sender (this is recommandation)

ex ) - (void)test:(id)sender

and add target like this.... [button addTarget:self action:@selector(test:) forControlEvents:UIControlEventTouchUpInside]

edited Jul 01 '12 at 23:07

answered Jul 01 '12 at 22:31

Luavis

49
1
6

Mehdzor · Answer 4 · 2012-07-01T19:31:30.537

-2

You might calling "test" method for NSString somewhere in your code.

edited Jul 01 '12 at 19:31

answered Jul 01 '12 at 19:23

Mehdzor

789
4
9
23

...what? Can you explain your answer further? – WendiKidd Jul 01 '12 at 19:25

Unrecognised selector on button press

4 Answers4