override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell{

            let cell = tableView.dequeueReusableCellWithIdentifier("tonggaocell", forIndexPath: indexPath) as! UITableViewCell //1

            let tonggao = tonggaos[indexPath.row] as TongGaoModel //2

            let nameLabel = cell.viewWithTag(101) as? UILabel

            nameLabel!.text = tonggao.title

        return cell

     }

   nameLabel!.text = tonggao.title

   返回值一直是nil，程序崩溃