Focus on next valid key view on iPhone

Question

Is there an iPhone equivalent for the NSResponder methods -selectNextKeyView or -nextValidKeyView from Mac OS X? I know about the -becomeFirstResponder method, but finding out which view to call that on is not very pretty when view hierarchies get more complicated.

There must be some kind of way to find this out as when I press tab when in the iPhone Simulator, focus does properly go to the next UITextField. This made me wonder what exactly happens when I press tab. Any ideas?

Update: This does exactly what I want, but _nextKeyResponder is private API, so a no-no. Is there any way to do a 'fake' tab key press without using private API?

- (BOOL)textFieldShouldReturn:(UITextField *)textField {
    // Try to find next responder
    UIView *nextResponder = (UIView *)[self.view _nextKeyResponder];

    if (nextResponder) {
        // Found next responder, so set it.
        [nextResponder becomeFirstResponder];
        [self.tableView scrollRectToVisible:[self.tableView convertRect:[nextResponder frame] fromView:nextResponder] animated:YES];
    } else {
        // Not found, so remove keyboard.
        [textField resignFirstResponder];
    }
    return NO; // We do not want UITextField to insert line-breaks.
}

Answer 1

There is not a public iOS equivalent for NSResponder's -selectKeyView or -nextValidKeyView.

When the first responder is an instance of UITextField, pressing tab instantiates a private subclass of UIEvent which is passed to -[UIApplication sendEvent:], which in turn calls -[UIView _nextKeyResponder].

-[UIView _nextKeyResponder] doesn't work quite the way you think it does. It treats the key view chain as a loop, so your else block will never be reached. For the same reason, even if there was a public API for synthesizing keyboard events, you probably wouldn't want to use it.

Instead, you probably want something more like UIWebView's UIToolbar-based form input accessory. Its buttons can be enabled and disabled when appropriate, and its delegate handles the actual button press actions.

To implement such a delegate in a general way, however, it might be helpful to look at how -[UIView _nextKeyResponder] is implemented.