上滑隐藏导航栏下拉显示导航栏效果

-(void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset{
if(velocity.y>0){
self.navigationController.navigationBar.hidden = YES;
}else{
self.navigationController.navigationBar.hidden = NO;
}
}