1、设置navbar触摸事件

2、tableview返回顶部

- (void)viewDidLoad {    [super viewDidLoad];        self.navigationController.navigationBar.userInteractionEnabled=YES;    UITapGestureRecognizer * tap=[[UITapGestureRecognizer alloc]initWithTarget:self action:@selector(scrollToTop:)];    [self.navigationController.navigationBar addGestureRecognizer:tap];}-(void)scrollToTop:(UITapGestureRecognizer *)sender{    [self.tableView setContentOffset:CGPointMake(0,-50) animated:YES];}