_searchBar = [[UISearchBaralloc]initWithFrame:CGRectMake(0,0, 320,44)];

    _searchBar.delegate =self;

    //不贴view下拉就会有阴影

    UIView *view = [[UIViewalloc] initWithFrame:CGRectMake(0,0, 320,44)];

    [view addSubview:_searchBar];

    self.tableView.tableHeaderView = view;

不能直接：

self.tableView.tableHeaderView = view;

ios7上UISearchBar和UITableView下拉刷新的时候阴影解决