在网上找的例子，感觉很实用，留着用
是用storyboard对控件加的约束，然后控件与视图底边距离的约束与.h或.m关联
@property (weak, nonatomic) IBOutlet NSLayoutConstraint *ceshi;
在viewDidLoad中注册通知：
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardComeout:) name:UIKeyboardWillShowNotification object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardComeout:) name:UIKeyboardWillHideNotification object:nil];
键盘弹出消失时设置控件的frame
-(void)keyboardComeout:(NSNotification *)notification
{
NSDictionary * userInfo = notification.userInfo;
CGRect frameOfKeyboard = [userInfo[UIKeyboardFrameEndUserInfoKey] CGRectValue];
CGRect frame = self.view.frame;
CGFloat height = frame.size.height - frameOfKeyboard.origin.y;
self.ceshi.constant = height;
}
就是这三步，感谢那位分享方法的大神，解决我一个大问题
