iOS 在NSNotification中包含CGRect等结构体

使用NSValue的valueWithCGRect:等方法转换成NSValue对象，而不是NSStringFromCGRect()等方法转换成NSString对象。

NSDictionary *userInfo = @{
                           @"UIKeyboardFrameBeginUserInfoKey" : [NSValue valueWithCGRect:CGRectMake(0, UIApplication.screenHeight - 216, UIApplication.screenWidth, 216)],
                           @"UIKeyboardFrameEndUserInfoKey" : [NSValue valueWithCGRect:CGRectMake(0, UIApplication.screenHeight - 258, UIApplication.screenWidth, 258)],
                           };
[NSNotificationCenter.defaultCenter postNotificationName:UIKeyboardWillChangeFrameNotification
                                                  object:nil
                                                userInfo:userInfo];