title: Button from parentVIewController still display on screen after pushViewController
body: <p>I am a newbie at IOS, and I get stuck in this weird problem
  it's really an easy demo, I just want jump to another viewController.</p>
  
  <pre><code>//parentViewController
  import UIKit
  import SnapKit
  
  class ViewController: UINavigationController {
  
  override func viewDidLoad() {
      super.viewDidLoad()
      // Do any additional setup after loading the view, typically from a nib.
      self.view.backgroundColor = UIColor.whiteColor()
      let button = UIButton()
      button.frame = CGRectMake(100, 100, 200, 100)
      button.backgroundColor = UIColor.greenColor()
      button.setTitle("Search Button", forState: UIControlState.Normal)
      button.addTarget(self, action: "buttonAction:", forControlEvents: UIControlEvents.TouchUpInside)
      self.view.addSubview(button)
  }
  
  func buttonAction(sender:UIButton!){
      print("Button tapped")
      let searchVC = MfSearchViewController()
      self.pushViewController(searchVC, animated: true)
  }
  
  override func didReceiveMemoryWarning() {
      super.didReceiveMemoryWarning()
      // Dispose of any resources that can be recreated.
  }
  
  }
  </code></pre>
  
  <p>and this is the target viewController</p>
  
  <pre><code>class MfSearchViewController:UIViewController{
      /// UI component
      var tableView:UITableView!
      var searchBar:UISearchBar!
      var searchLabel:UILabel!
      ///
      var dataSource = NSMutableArray()
      var currentIndexPaht: NSIndexPath?
      var screenObj = UIScreen.mainScreen().bounds
  
  
  
  
      override func viewDidLoad() {
          super.viewDidLoad()
          for index in 0...12{
              let model = SearchResultModel(searchWord: "java\(index+1)", searchResult: "1500")
              dataSource.addObject(model)
          }
          self.view.backgroundColor = UIColor.lightGrayColor()
          tableView = UITableView(frame: self.view.bounds, style: UITableViewStyle.Plain)
          //tableView = UITableView(frame: CGRectMake(0,20,screenObj.width,screenObj.height), style: UITableViewStyle.Grouped)
          tableView.delegate = self
          tableView.dataSource = self
          view.addSubview(tableView)
          self.title = "target"
  
  
      }
  
      override func didReceiveMemoryWarning() {
          super.didReceiveMemoryWarning()
          // Dispose of any resources that can be recreated.
      }
  
  
      /*
      // MARK: - Navigation
  
      // In a storyboard-based application, you will often want to do a little preparation before navigation
      override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
          // Get the new view controller using segue.destinationViewController.
          // Pass the selected object to the new view controller.
      }
      */
  
  }
  
  extension MfSearchViewController: UITableViewDataSource{
  
      func numberOfSectionsInTableView(tableView: UITableView) -&gt; Int {
          return 1
      }
  
      func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -&gt; UITableViewCell {
          let cellIdentifier: String = "SearchResultCellIdentifier"
          // may be no value, so use optional
          var cell: SearchResultCell? = tableView.dequeueReusableCellWithIdentifier(cellIdentifier) as? SearchResultCell
          if cell == nil { // no value
              cell = SearchResultCell(style: UITableViewCellStyle.Default, reuseIdentifier: cellIdentifier)
          }
          let model: SearchResultModel? = dataSource[indexPath.row] as? SearchResultModel
          cell!.configureCell(model)
          return cell!
      }
  
      func tableView(tableView: UITableView,numberOfRowsInSection section: Int) -&gt; Int {
          return dataSource.count
      }
  
     }
  
  extension MfSearchViewController: UITableViewDelegate{
      func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
          print(indexPath);
      }
  
  }
  </code></pre>
  
  <p>but after pushViewcontroller, button from parentViewController still there...plz help me....many thanks...</p>
  
  <p><a href="https://i.stack.imgur.com/w9e9G.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/w9e9G.png" alt="enter image description here"></a></p>