prepareForSegue and PerformSegueWithIdentifier sender

There are, effectively, two ways you can trigger a segue. The first is via an action on a UI element in Interface Builder, the second is using performSegueWithIdentifier:sender: in your code. I say 'effectively', because under the covers, when the scene is loaded from the storyboard, an action handler is configured that ultimately calls performSegueWithIdentifier:sender:

When performSegueWithIdentifier:sender: is called, the segue object is delivered to your view controller's prepareForSegue:sender: function.

In the case where the segue was initiated by an action on a UI element then the sender will be that UI element (i.e. if it is an action connection on a UIButton then the sender will be the UIButton instance).

If the segue is initiated by your code calling performSegueWithIdentifier:sender: then the sender will be whatever object you passed as the sender. This could be your view controller, a button, an array, anything. So yes, if you pass "Hello World" to performSegueWithIdentifier:sender: as the sender value then this will be the sender in prepareForSegue:sender:

In terms of the order of operations:

1. performSegueWithIdentifier:sender is called, either by your code or as a result of an action on a UI element
2. If your view controller implements shouldPerformSegueWithIdentifier:sender: then this function is called. If this function returns false then the segue is cancelled
3. The segue object and destination view controller object are created
4. If your view controller implements prepareForSegue:sender: then this function is called.
5. Once prepareForSegue:sender: returns, the segue completes.

The performSegue method calls a segue to be performed from one view to another. Before the segue actually takes place, the prepareForSegue method is called, and if you want to pass data between the views, you'd do it there.

The performSegue method doesn't take the parameter you want to send. It's only used to call the segue in the first place. Any data that you want to send will be done through prepareForSegue.

Here's an example.

override func viewDidLoad() {
    super.viewDidLoad()

    // Do any additional setup after loading the view.

    performSegueWithIdentifier("test", sender: self)
    //You can set the identifier in the storyboard, by clicking on the segue
}

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if segue.identifier == "test"{
        var vc = segue.destinationViewController as! RandomViewController
        vc.data = "Data you want to pass"
        //Data has to be a variable name in your RandomViewController
    }
}

Let me know if this helps!

The_Curry_Man's answer worked for me. Here's an update of his code for Swift 3.

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view.

    performSegue(withIdentifier: "test", sender: self)
    //You can set the identifier in the storyboard, by clicking on the segue
}

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "test"{
        var vc = segue.destinationViewController as! RandomViewController
        vc.data = "Data you want to pass"
        //Data has to be a variable name in your RandomViewController
    }
}