在通过模态方式执行Segue之后获得“发现无”异常

Question

I have to view controllers, from first controller's menu item click, a segue is performed by 'Present Modally' Segue which will open the second viewController (acting as a menu) when i press Refresh button on the second VC, it is calling the method from the first VC To refresh its data and load it on tableView. the problem is it is call the method from second to first VC but is returning nil on this line.

    self.tableView.dataSource = self 

i think it is because the first VC is not active properly as it is in the background ( the second VC's background is transparent so that i can see the first VC at the back ). i'm new to swift and i don't know how to deal with it.

EDIT: This is the refresh method

   func refresh() {  

   //   self.dismiss(animated: true, completion: nil)
  //  present(DayView_Controller, animated: true, completion: nil)

   // self.dismiss(animated: true, completion: nil) // it is dismissing the first view controller instead of second



    ////////
    Extensions.ShowAlert(self.pwait, sender: self) // here it causing the exception on viewDidLoad
    let defaults = UserDefaults.standard
    let date = Date()
    let formatter = DateFormatter()
    formatter.dateFormat = "MM/d/yyyy"
    let finaldate = formatter.string(from:date)
    if Reachability.isConnectedToNetwork(){
    // all the services are being call and getting reloaded on tableview
  }

 override func viewDidLoad() {
    super.viewDidLoad()


    self.tableView.dataSource = self // exception here
  }

2nd EIDT: now i'm dismissing the 2nd VC on the refresh click and call the method from 1st VC on the completion, still getting the same error.

 @IBAction func Refresh_CLick(_ sender: Any) {
    self.dismiss(animated: true, completion: {
        DayView_Controller().refresh()

    })
  //  DayView_Controller().refresh()

}

Answer 1

I believe, you need to do something like this:

1) Create protocol:

protocol RefreshDelegate {
    func dataChanged(data: [Items])
}

2) In your second view controller add:

var delegate: RefreshDelegate ?

if let del = delegate {
     del.dataChanged(data: items) // your refreshed data
}

3) In your first view controller add extension:

extension FirstViewController: RefreshDelegate {
    func dataChanged(data: [Items]) {
         // update your tableView data -> then reload
    }
}

Something like this. You should understand main idea.

Hope it helps

Answer 2

Use Delegate to refresh data

protocol RefreshDelegate: class {
    func refreshData(data: Int)
}

In your first view controller add delegate

class ViewController: UIViewController, UITableViewDelegate, UITableViewDataSource, RefreshDelegate {

In your prepare for segue method set delegate

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "go" {
        let viewController:SecondViewController = segue.destination as! SecondViewController
        viewController.refreshDelegate = self
    }

}

// Delegate
    func refreshData(data: Int) {
        tableData = data
        self.tableView.reloadData()
    }

In second view controller add variable for delegate

weak var refreshDelegate: RefreshDelegate?

Now call refresh delegate from second view controller

@IBAction func refreshTapped(_ sender: UIButton) {
    self.dismiss(animated: true, completion: {
        self.refreshDelegate?.refreshData(data: 10)
    })
}