Problems with Navigation Controller (back button and prepareForSegue) - ios

Question

I promise that I'm completely new to Xcode and Swift, so I know I am making silly mistakes but I don't know where. This is part of my iOS app storyboard:
where the segue between the first table view and the second navigation controller is called myTaskDetailSegue and its type is Show (e.g. Push). Now I have some problems:
Neither in the first table view controller nor in the second the back button is showed and I don't know why. Many people told me that navigation bar and back button are as default in navigation controllers but they did not appear
In the class of the first table view controller here is the method prepareForSegue()
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if (segue.identifier == "myTaskDetailSegue" ) {
let indexPath = self.tableView.indexPathForSelectedRow()
let task = self.taskCollection[indexPath!.row] as Task
let controller = (segue.destinationViewController as! UINavigationController).topViewController as! DetailsMyTasksViewController
controller.detailItem = task
println("segue mostra task \(task.id)")
controller.navigationItem.leftItemsSupplementBackButton = true
}
}
so you can read that the segue identifier is correct but when a row is tapped nothing happens and the second table view controller is not showed.
I don't really know what I am missing because of my inexperience.
Here is the complete storyboard:

Answer 1

You don't need two UINavigationController's to what you want to achieve. Is important to note that every time you push(with a segue or manually) a new UIViewController it's added to the navigation stack.
According to Apple:
Pushing a view controller displays its view in the navigation interface and updates the navigation controls accordingly. You typically push a view controller in response to user actions in the current view controller—for example, in response to the user tapping a row in a table.
So you can remove the second UINavigationController in your Storyboard and make the segue directly to your DetailsMyTaskViewController and update your prepareForSegue like in the following way:
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if (segue.identifier == "myTaskDetailSegue" ) {
let indexPath = self.tableView.indexPathForSelectedRow()
let task = self.taskCollection[indexPath!.row] as Task
let controller = segue.destinationViewController as! DetailsMyTasksViewController
controller.detailItem = task
println("segue mostra task \(task.id)")
}
}
And your back button should appear by default as you said before. Nevertheless I strongly recommend you read the following two guides :
UINavigationViewController
View Controller Programming Guide for iOS
For a better understanding of the navigation stack, etc.
I hope this help you.