"unrecognized selector" error when trying to dismiss keyboard

I'm trying to dismiss the keyboard when the user presses a "cancel" UIBarButtonItem. When I click the cancel button however, I get a SIGABRT with the "unrecognized selector sent to instance" error.

My code to create the cancel button is:

- (void)keyboardWasShown:(NSNotification*)aNotification
{
    //Add cancel button to navigation bar
    UIBarButtonItem *dismissKeyboardBttn = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemCancel target:self action:@selector(dismissKeyboard:)];
    self.navigationItem.rightBarButtonItem = dismissKeyboardBttn;
}

And to dismiss the keyboard I have this method:

- (void)dismissKeyboard:(id)sender
{
    [activeField resignFirstResponder];
    //^^This line causes the SIGABRT^^
}

It seems pretty straightforward. Any ideas?

UPDATE: activeField is just a UITextField I'm using to move my scrollView to the UITextField the user is currently editing. It is set in these two methods:

- (void)textFieldDidBeginEditing:(UITextField *)textField 
{ 
    activeField = textField; 
}
- (void)textFieldDidEndEditing:(UITextField *)textField 
{ 
    activeField = nil; 
}

UPDATE 2: Interesting, I 开发者_如何学Chave registered my ViewController to receive keyboard notifications, and when I try to dismiss the keyboard using the "textFieldShouldReturn" method, I get the same error. Here is my textFieldShouldReturn code:

- (BOOL)textFieldShouldReturn:(UITextField *)textField {

    if ([textField canResignFirstResponder])
    {
        [textField resignFirstResponder];
    }

    return YES;
}

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I am in a situation and do as follows in the current view controller:

In the header file, create an IBAction for the text field which became the first responder and bring up the keyboard:

- (IBAction)textFieldDidBeginEditing:(UITextField *)textField;

In the implementation file, create a method which creates the bar button (in my case, a "Done" button) and adds it to the right side of the navigation bar. Simultaneously, I create a target action pairing between the TextField (which has become the first responder

- (void)textFieldDidBeginEditing:(UITextField *)textField
{
    // create new bar button with "Done" as text
    // set the target of the action as the text field (since we want the text field to resign first responder status and dismiss the keyboard)
    // tell the text field to resign with the stock 'resignFirstResponder' selector
    UIBarButtonItem *bbi = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemDone
                                                                         target:textField
                                                                         action:@selector(resignFirstResponder)];

    // add the button with target/action pairing to the navigation bar
    [[self navigationItem] setRightBarButtonItem:bbi];
}

Additionally, if you want the button to disappear after I click it (and the keyboard goes away), I use the textFieldDidEndEditing since editing has now completed with the first responder recognition:

- (void)textFieldDidEndEditing:(UITextField *)textField
{
    [[self navigationItem] setRightBarButtonItem:nil];
}

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What is activeField? If it's a UIResponder, it should respond to resignFirstResponder. So maybe it's not. UIViews and UIViewControllers are UIResponders.

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Morningstar is right, what is the activeField, is it an id and you possible need to add a cast: (UIButton*)? Also, I always add this when resignFirstResponder:

if(myObject canResignFirstResponder){

}