UIButton "addTarget" crashes app - objective-c

Question

Just learning to add actions with code in my .m file and my first attempt throws an exception and crashes the app.
This is an authentication script that I hope will communicate with my web server. Here is the relevant code (this is all in the .m file, very simple .h file):
.h (header) file:
#import <UIKit/UIKit.h>
#interface Login_ViewController : UIViewController <UITextFieldDelegate>
#end
.m (implementation) file:
- (void)viewDidLoad {
UILabel *emailLabel = [[UILabel alloc] initWithFrame:CGRectMake(31.0f, 75.0f, 256.0f, 20.0f)];
emailLabel.text = #"Email Address";
emailLabel.backgroundColor = [UIColor grayColor];
emailLabel.textColor = [UIColor whiteColor];
UITextField *emailField = [[UITextField alloc] initWithFrame:CGRectMake(31.0f, 100.0f, 256.0f, 32.0f)];
emailField.delegate = self;
emailField.placeholder = #"Enter email address";
emailField.borderStyle = UITextBorderStyleRoundedRect;
[self.view addSubview:emailLabel];
[self.view addSubview:emailField];
UILabel *passLabel = [[UILabel alloc] initWithFrame:CGRectMake(31.0f, 175.0f, 256.0f, 20.0f)];
passLabel.text = #"Password";
passLabel.backgroundColor = [UIColor grayColor];
passLabel.textColor = [UIColor whiteColor];
UITextField *passField = [[UITextField alloc] initWithFrame:CGRectMake(31.0f, 200.0f, 256.0f, 32.0f)];
passField.delegate = self;
passField.placeholder = #"Enter Password";
passField.borderStyle = UITextBorderStyleRoundedRect;
passField.secureTextEntry = YES;
UIButton *loginButton = [[UIButton alloc] initWithFrame:CGRectMake(31.0f, 275.0f, 256.0f, 32.0f)];
[loginButton setTitle:#"Login" forState:UIControlStateNormal];
[loginButton addTarget:self action:#selector(authenticate) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:passLabel];
[self.view addSubview:passField];
[self.view addSubview:loginButton];
[self.view setBackgroundColor: [UIColor grayColor]];
UIAlertView *noAccount = [[UIAlertView alloc] initWithTitle:#"Welcome to T-of-U" message:#"Please enter your TofU credentials." delegate:self cancelButtonTitle:#"continue" otherButtonTitles: nil];
[noAccount show];
[super viewDidLoad];
}
also in the .m file (IBAction for the button):
-(IBAction)authenticate:(id)sender{
// This will be the validation code
// if we validate we will set the default Setting with accountID here.
UIAlertView *auth1 = [[UIAlertView alloc] initWithTitle:#"You clicked a button" message:#"Oh, do you want to login do you?" delegate:self cancelButtonTitle:#"Sure.. Why not!" otherButtonTitles: nil];
[auth1 show];
}
I am using a storyboard with a View that has a custom class of login_ViewController and it loads successfully based on a check for a local setting for account ID. This window is only pulled up if they have not logged in before, so I can authenticate and get that account ID to store locally. I am still experimenting with programmatically creating all these items as you can see in the viewDidLoad section.
Is this failing because I don't have the button/IBAction reference in the .h file , or is it ok to use the addTarget method where its all in the .m file?
Crash info from the log:
2012-01-08 04:54:32.868 TofU-5[10452:10103] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[Login_ViewController authenticate]: unrecognized selector sent to instance 0x6c94780'

Answer 1

Your fix may be as easy as:
[loginButton addTarget:self action:#selector(authenticate:) forControlEvents:UIControlEventTouchUpInside];
(add a COLON after the authenticate name in your #selector). If a method takes any parameter, there will be a colon after it and for the run time environment to be able to send a message to it, that colon needs to be included in the selector of the action target.
I hope this makes sense and helps you out!
p.s. it wouldn't hurt to add
-(IBAction)authenticate:(id)sender
to the .h file.
IBAction here is an abbreviation for InterfaceBuilder-Action so this actually helps a lot more if you're building the interface in a XIB file. Because you're setting the target programatically, you could just use -(void) authenticate (no colon, because your method uses or needs no parameters), but don't do this yet until you get more overall experience with Objective C coding and actions.