Swift：将数据从ViewController中的tableView传递到另一个ViewController

Question

I'm trying to pass the indexPath.row data from the selected cell to the next view controller using both the didSelectCellAtIndexPath and the prepareForSegue methods but the value isnt passing through.

Code for both ViewControllers is show below:

   import UIKit

class MainMenu: UIViewController, UITextFieldDelegate, UITableViewDelegate, UITableViewDataSource {

// array of the menu options

let mainMenuOptions = ["Exercises 1", "Exercises 2", "Exercises 3"]

// UITableView

@IBOutlet weak var exerciseOptions: UITableView!


override func viewDidLoad() {
    super.viewDidLoad()
    exerciseOptions.delegate = self
    exerciseOptions.dataSource = self
    // Do any additional setup after loading the view.
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

// Table configuration

func numberOfSectionsInTableView(tableView: UITableView) -> Int {
    return 1
}

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    let cellIdentifier = "ExercisesTableViewCells"
    let cell = tableView.dequeueReusableCellWithIdentifier(cellIdentifier, forIndexPath: indexPath) as! ExercisesTableViewCell
    cell.textLabel!.text = mainMenuOptions[indexPath.row]
    return cell
    }

func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return 3
}

// Segue to VC based on row selected
func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {

    if indexPath.row == 0{
        self.performSegueWithIdentifier("SegueToExercises", sender: self)
    }
    else if indexPath.row == 1{
        self.performSegueWithIdentifier("SegueToExercises", sender: self)
    }
    else{
        self.performSegueWithIdentifier("SegueToReminders", sender: self)
    }
}

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if (segue.identifier == "SegueToExercise"){

        let viewController = segue.destinationViewController as? ExerciseMenu
        viewController!.mainMenuValue = exerciseOptions.indexPathForSelectedRow!.row


    }

}

For the Second View Controller:

   import UIKit

class ExerciseMenu: UIViewController, UITextFieldDelegate, UITableViewDelegate, UITableViewDataSource {

@IBOutlet weak var exerciseOptionsTitle: UILabel!
@IBOutlet weak var exerciseOptionsTable: UITableView!
@IBAction func beginWorkout(sender: AnyObject) {
}

// receives data from MainMenu
var mainMenuValue: Int!

override func viewDidLoad() {
    super.viewDidLoad()
    exerciseOptionsTable.delegate = self
    exerciseOptionsTable.dataSource = self
    // Do any additional setup after loading the view.
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}


func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    let cellIdentifier = "ExerciseMenuCell"
    let cell = tableView.dequeueReusableCellWithIdentifier(cellIdentifier, forIndexPath: indexPath) as! ExercisesTableViewCell
    cell.textLabel!.text = String(mainMenuValue)
    return cell
    }

func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return 1
}

Answer 1

See this thread for possible explanations for this behavior. The first step of troubleshooting would be to put a breakpoint in your prepareForSegue method to see if exerciseOptions.indexPathForSelectedRow is already nil at that point, in which case something is happening before the segue even occurs that's messing with the value (which the link above can help you diagnose).

Try making a property in your table view controller called something like selectedRow, and in didSelectRowAtIndexPath , set self.selectedRow = indexPath.row . This way you have your own variable that'll be more reliable than exerciseOptions.indexPathForSelectedRow . Then change the code in prepareForSegue appropriately. So to give you the full methods as I'm envisioning them:

(As a property of the first view controller) var selectedRow: Int?

func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {

  if indexPath.row == 0{
    self.performSegueWithIdentifier("SegueToExercises", sender: self)
    self.selectedRow = 0
  }
  else if indexPath.row == 1{
    self.performSegueWithIdentifier("SegueToExercises", sender: self)
    self.selectedRow = 1

  }
  else{
    self.performSegueWithIdentifier("SegueToReminders", sender: self)
    self.selectedRow = indexPath.row
  }
}


override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
  if (segue.identifier == "SegueToExercise"){

    let viewController = segue.destinationViewController as? ExerciseMenu
    viewController!.mainMenuValue = self.selectedRow!


  }
}

Disclaimer: I'm still learning Swift, so my judgment regarding optionals/optional unwrapping might be unideal for a technical reason I'm not aware of, but the overall theory here is sound, I think.