tableview中增加了头视图后，初始位置显示不正常

override func viewDidLoad() {
    super.viewDidLoad()
    
    self.view.backgroundColor = UIColor(rgb: 0xeeeeee)
    self.navigationItem.leftBarButtonItem = UIBarButtonItem(image: UIImage(named: "back_bt_7"), style: .Plain, 
        target: self, action: #selector(AppSettingViewController.popPrevious))
    tableview.delegate = self
    tableview.dataSource = self
    self.view.addSubview(tableview)
    
    tableview.snp_makeConstraints { (make) -> Void in
        make.edges.equalTo(self.view)
    }
    
    self.automaticallyAdjustsScrollViewInsets = false

    let headImage = UIImage(named: "user_background")
    headHeight = headImage!.size.height
    tableview.contentInset = UIEdgeInsetsMake(headHeight, 0, 0, 0)
   
    
    tableview.registerClass(YSettingCell.self, forCellReuseIdentifier: YSettingCell.CellIdentifier)
    tableview.registerClass(UITableViewCell.self, forCellReuseIdentifier: "logoutIdentifier")
    tableview.setContentOffset(CGPoint(x: 0, y: -headHeight), animated: true)

    self.setupHeadView()

    self.setupData()
}