给 view 注册一个点击手势，在 view 点击时放弃“第一响应者”

#pragma mark 点击空白处关闭键盘
- (void)viewDidLoad {
    [super viewDidLoad];
    //点击空白处关闭键盘
    UITapGestureRecognizer* tapGr = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(viewTapped:)];
    tapGr.cancelsTouchesInView = NO;
    [self.view addGestureRecognizer:tapGr];
}

-(void)viewTapped:(UITapGestureRecognizer *)tapGr{
    [_noteContent resignFirstResponder];
}