Question

I am trying to create a simple button, textfield, label program in objective c and I am having button problems.

In file viewController.m, I have the following code:

UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
[button addTarget:self action:@selector(buttonPressed) forControlEvents:UIControlEventTouchDown];

[button setTitle:@"Look up" forState:UIControlStateNormal];
button.frame = CGRectMake(20,108,97,37);
[self.view addSubview:button];

and

- (IBAction) buttonPressed:(id) sender  {
[_textField resignFirstResponder];
_label.text = textField.text;
}

From what I understand, the button is supposed to to take what is in my text box and put it into a label after I click this button. But instead, pressing the button takes me main.m on the return line. And it says the program is paused. If I try to use the program again, it just doesn’t work. I have cross examined this button snippet with other code online and can’t quite figure out why mine is failing.

Answer 1

You have missed a colon on this line

[button addTarget:self action:@selector(buttonPressed) forControlEvents:UIControlEventTouchDown];

Your button is calling a method that doesn’t exist, thats why it is crashing.

should be

[button addTarget:self action:@selector(buttonPressed:) forControlEvents:UIControlEventTouchDown];

OR… change the signature of your buttonPressed method from

- (IBAction) buttonPressed:(id) sender;

to

    - (IBAction) buttonPressed;

you should have seen a message in your log, something like

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[ViewController buttonPressed]: unrecognized selector sent to instance