How can I dismiss the keyboard if a user taps off the on-screen keyboard?

You’ll need to add an UITapGestureRecogniser and assign it to the view, and then call resign first responder on the textfield on it’s selector.

The code:

In viewDidLoad

UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self
                                                                      action:@selector(dismissKeyboard)];

[self.view addGestureRecognizer:tap];

In dismissKeyboard:

-(void)dismissKeyboard {
       [aTextField resignFirstResponder];
}

(Where aTextField is the textfield that is responsible for the keyboard)

OPTION 2

If you can’t afford to add a gestureRecognizer then you can try this

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    UITouch * touch = [touches anyObject];
    if(touch.phase == UITouchPhaseBegan) {
        [aTextField resignFirstResponder];
    }
}