iPad keyboard will not dismiss if modal ViewController presentation style is UIModalPresentationFormSheet

I found that `disablesAutomaticKeyboardDismissal` and adding a `disablesAutomaticKeyboardDismissal` function didn't work for my `UITextField` in a modal dialog.

The onscreen keyboard just wouldn't go away.

My solution was to *disable* all text-input controls in my dialog, then re-enable the relevant ones a fraction of a second later.

It seems as though when iOS sees that none of the `UITextField` controls are enabled, then it *does* get rid of the keyboard.

I solved this by using the `UIModalPresentationPageSheet` presentation style and resizing it immediately after I present it. Like so:

viewController.modalPresentationStyle = UIModalPresentationPageSheet;
viewController.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;
[self presentModalViewController:viewController animated:YES];
viewController.view.superview.autoresizingMask =
UIViewAutoresizingFlexibleTopMargin |
UIViewAutoresizingFlexibleBottomMargin;
viewController.view.superview.frame = CGRectMake(
viewController.view.superview.frame.origin.x,
viewController.view.superview.frame.origin.y,
540.0f,
529.0f
);
viewController.view.superview.center = self.view.center;
[viewController release];

Swift 4.1:
extension UINavigationController {
override open var disablesAutomaticKeyboardDismissal: Bool {
return false
}
}

In the view controller that is presented modally, just override `disablesAutomaticKeyboardDismissal` to return `NO`:

```objc
- (BOOL)disablesAutomaticKeyboardDismissal {
return NO;
}
```