iPad keyboard will not dismiss if modal view controller presentation style is UIModalPresentationFor

在ipad上present 一个 navigation controller 时，present后弹出的keyboard，不能够 dismiss 掉。即使 textfield resignFirstResponder，keyboard也不会消失。

Problem:

在iPad keyboard上发现一个问题，当viewController在Navigation controller下以模态视图弹出，并且navigationController.modalPresentationStyle = UIModalPresentationFormSheet时，点击done按钮，软键盘不撤销，即使 textfield resignFirstResponder了。

Solution:

当模态视图在 UINavigationControlle下显示，我们需要设置 navigation controller的disablesAutomaticKeyboardDismissal属性，我们可以通过添加类别实现这个。

File: UINavigationController+KeyboardDismiss.h

#import 

@interface UINavigationController (KeyboardDismiss)

- (BOOL)disablesAutomaticKeyboardDismissal;

@end

File: UINavigationController+KeyboardDismiss.m

#import "UINavigationController+KeyboardDismiss.h"

@implementation UINavigationController(KeyboardDismiss)

- (BOOL)disablesAutomaticKeyboardDismissal

{

    return NO;

}

@end

在需要用到的ViewController文件中导入创建的类别即可。