Pass Data Between Two View Controllers Using a Custom Tab Bar Controller Class

Question

I am attempting to pass data from one viewcontroller to another using a Tab Bar Controller. I have implemented a custom Tab Bar Controller class. Here is my code for this class:

class CustomTabBarControllerClass: UITabBarController, UITabBarControllerDelegate {

    override func awakeFromNib() {
        self.delegate = self;
    }

    func tabBarController(tabBarController: UITabBarController, didSelectViewController viewController: UIViewController) {
        var logView = SecondViewController()
        logView.log.append("Testing 123")
    }

}

As you can see in my code, I am creating an instance of SecondViewController with the logView variable. In my SecondViewController class, I have a log array setup that will hold the value being passed from my CustomTabBarControllerClass class. Here is my code for my SecondViewController.

class SecondViewController: UIViewController, UITableViewDataSource, UITableViewDelegate {

    var log = [String]()

    func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return log!.count
    }

    func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCellWithIdentifier("logCell", forIndexPath: indexPath) as UITableViewCell

        cell.textLabel.text = log![indexPath.row]

        return cell
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        println(log!) //fatal error: unexpectedly found nil while unwrapping an Optional value
    }

}

In my viewDidLoad() function, I am attempting to print the log to the console with println(log!). When this code runs, I am presented with following error: fatal error: unexpectedly found nil while unwrapping an Optional value. So how would I go about passing data between the two viewcontrollers?

Update

The didSelectViewController function has been updated with the code below, however, I am still receiving the same error message.

func tabBarController(tabBarController: UITabBarController, didSelectViewController viewController: UIViewController) {
        var logView = self.viewControllers![0] as SecondViewController
        logView.log?.append("Testing 123")
    }

Answer 1

Your tab bar controller already has an instance of SecondViewController, so you shouldn't be instantiating a new one. Use the tab bar controller's viewControllers property to access the one you want (presumably, from the name, the one at index 1).

class ViewController: UIViewController {

    var log = [String]()

    override func viewDidAppear(animated: Bool) {
        super.viewDidAppear(animated)
        println(log)
    }
}

In the tab bar controller,

class RDTabBarController: UITabBarController , UITabBarControllerDelegate{

    override func viewDidLoad() {
        super.viewDidLoad()
        self.delegate = self
    }

    func tabBarController(tabBarController: UITabBarController, didSelectViewController viewController: UIViewController) {
        var logView = self.viewControllers![1] as ViewController
        logView.log.append("Testing 123")
    }

}