Can't pass variable into prepareForSegue in Swift? - ios

Question

I'm trying to pass selectedName to VC #2 (BrandTableViewController). If I println(selectedName) in viewDidDisappear I get the value, however, the value is nil when it's in prepareForSegue? Can anyone see why?
import UIKit
import CoreData
class NameTableViewController: UITableViewController, UITableViewDelegate {
//Changes [String] to [NSManagedObject]
var people = [NSManagedObject]()
#IBOutlet var nameTableView: UITableView!
var selectedName: Person?
override func viewDidLoad() {
super.viewDidLoad()
title = "\"People\""
nameTableView.delegate = self
// Uncomment the following line to preserve selection between presentations
// self.clearsSelectionOnViewWillAppear = false
// Uncomment the following line to display an Edit button in the navigation bar for this view controller.
// self.navigationItem.rightBarButtonItem = self.editButtonItem()
// Retreive the managedObjectContext from AppDelegate
let managedObjectContext = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext
// Print it to the console
println(managedObjectContext)
}
// Mark: - Add Button Alert
#IBAction func addButton(sender: AnyObject) {
var alert = UIAlertController(title: "New name",
message: "Add a new name",
preferredStyle: .Alert)
let saveAction = UIAlertAction(title: "Save",
style: .Default) { (action: UIAlertAction!) -> Void in
let textField = alert.textFields![0] as! UITextField
self.saveName(textField.text)
self.tableView.reloadData()
}
let cancelAction = UIAlertAction(title: "Cancel",
style: .Default) { (action: UIAlertAction!) -> Void in
}
alert.addTextFieldWithConfigurationHandler {
(textField: UITextField!) -> Void in
}
alert.addAction(saveAction)
alert.addAction(cancelAction)
presentViewController(alert,
animated: true,
completion: nil)
}
//function to save a name (code from: http://www.raywenderlich.com/85578/first-core-data-app-using-swift)
func saveName(name: String) {
//1
let appDelegate =
UIApplication.sharedApplication().delegate as! AppDelegate
let managedContext = appDelegate.managedObjectContext!
//2
let entity = NSEntityDescription.entityForName("Person",
inManagedObjectContext:
managedContext)
let person = NSManagedObject(entity: entity!,
insertIntoManagedObjectContext:managedContext)
//3
person.setValue(name, forKey: "name")
//4
var error: NSError?
if !managedContext.save(&error) {
println("Could not save \(error), \(error?.userInfo)")
}
//5
people.append(person)
}
// MARK: - Table view data source
// override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
// // #warning Potentially incomplete method implementation.
// // Return the number of sections.
// return 1
// }
override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
// #warning Incomplete method implementation.
// Return the number of rows in the section.
return people.count
}
private struct Storyboard {
static let CellReuseIdentifier = "Name"
}
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier(Storyboard.CellReuseIdentifier, forIndexPath: indexPath) as! UITableViewCell
let person = people[indexPath.row]
cell.textLabel!.text = person.valueForKey("name") as? String
return cell
}
override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
let row = self.tableView.indexPathForSelectedRow()!.row
println("row \(row) was selected")
selectedName = people[indexPath.row] as? Person
println(selectedName)
// if let unWrappedSelectedName = selectedName {
// // println(unWrappedSelectedName)
// }
// else {
// println("no person was selected in didSelectRowAtIndexPath")
// }
}
// Override to support conditional editing of the table view.
override func tableView(tableView: UITableView, canEditRowAtIndexPath indexPath: NSIndexPath) -> Bool {
// Return NO if you do not want the specified item to be editable.
return true
}
// Override to support editing the table view.
override func tableView(tableView: UITableView, commitEditingStyle editingStyle: UITableViewCellEditingStyle, forRowAtIndexPath indexPath: NSIndexPath) {
if editingStyle == .Delete {
let personToDelete = people[indexPath.row]
//abstract this into helper function later
let appDelegate =
UIApplication.sharedApplication().delegate as! AppDelegate
let managedContext = appDelegate.managedObjectContext!
managedContext.deleteObject(personToDelete)
self.fetchCoreData()
tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)
} else if editingStyle == .Insert {
// Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view
}
}
/*
// Override to support rearranging the table view.
override func tableView(tableView: UITableView, moveRowAtIndexPath fromIndexPath: NSIndexPath, toIndexPath: NSIndexPath) {
}
*/
/*
// Override to support conditional rearranging of the table view.
override func tableView(tableView: UITableView, canMoveRowAtIndexPath indexPath: NSIndexPath) -> Bool {
// Return NO if you do not want the item to be re-orderable.
return true
}
*/
override func viewWillAppear(animated: Bool) {
super.viewWillAppear(animated)
fetchCoreData()
}
//Helper Function to Fetch Core Data
func fetchCoreData() {
//1
let appDelegate =
UIApplication.sharedApplication().delegate as! AppDelegate
let managedContext = appDelegate.managedObjectContext!
//2
let fetchRequest = NSFetchRequest(entityName:"Person")
//3
var error: NSError?
let fetchedResults = managedContext.executeFetchRequest(fetchRequest,
error: &error) as? [NSManagedObject]
if let results = fetchedResults {
people = results
} else {
println("Could not fetch \(error), \(error!.userInfo)")
}
}
// MARK: - Navigation
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if let btvc = segue.destinationViewController as? BrandsTableTableViewController {
if let identifer = segue.identifier {
if identifer == "segueToBrands" {
btvc.selectedName = selectedName
println(selectedName)
}
}
}
else {
println("we have a segue problem")
}
}

Answer 1

The prepareForSegue: method is called before tableView:didSelectRowAtIndexPath: method.And I saw that you only assign selectedName in method didSelectRowAtIndexPath.So selectedName will always be nil in prepareForSegue.
You can assign selectedName in tableView:willSelectRowAtIndexPath:
override func tableView(tableView: UITableView, willSelectRowAtIndexPath indexPath: NSIndexPath) {
let row = self.tableView.indexPathForSelectedRow()!.row
println("row \(row) was selected")
selectedName = people[indexPath.row] as? Person
println(selectedName)
}

Answer 2

In your preprareForSegue() you can access the selected cell (or cells) as such:
override func prepareForSegue (segue: UIStoryboardSegue, sender: AnyObject?) {
switch segue.identifier ?? "" {
case "theSegue":
if let indexPath = tableView.indexPathForSelectedRow () {
// get what you need from the cell or the DataSource object
let controller = segue.destinationViewController as! PersonController
controller.person = people[indexPath.row]
}
// ...
}
}