Pass a string to a second view controller

Question

I'm trying to pass a string to a second view controller. The string is the title of the new view controller. To pass the string I can use 2 solutions and both solutions work correctly but for me is not so clear the difference. Can someone explain me the differences?

Here the first solution:

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject!) {
        if (segue.identifier == "settime") {
            let svc = segue.destinationViewController as! timeSetting;
            //Assign the new title
            svc.toPass = "New Title"

        }
    }

Here the second solution:

   override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject!) {
        if (segue.identifier == "settime") {
            let svc = segue.destinationViewController as? timeSetting;
            //Assign the new title
            svc!.toPass = "New Title"

        }
    }

The variable toPass is defined in this way in the second viewController:

 var toPass:String = "Title"

Answer 1

Both of your code is working and it works in the same way.

The only difference is about the optional casting.

Optional in Swift

Answer 2

They are the same.

If there is a difference, it is the time of unwrap the optional value. In the first solution, the type of svc is timeSetting . In the second solution, the type of svc is timeSetting? .

Answer 3

Both solutions will perform the same action. In my opinion, the first solution is preferred because it express your intent more precisely.

By stating let svc = segue.destinationViewController as! timesetting let svc = segue.destinationViewController as! timesetting you state that the destination view controller is certain to be of the type timesetting .

The second form tests to see if the destination view controller is of the type timeSetting . If it is, then the variable svc will have a non-nil value.

If you were to define another segue of the same name that presents a different type of view controller, then both solutions will fail; the first one on the as! clause and the second one when you try to unwrap svc! , which would be nil.

Answer 4

两者都可以使用，但我认为最好的方法是像下面这样拆开可选组件：

if let svc = segue.destinationViewController as? timeSerting { svc.toPass = "xx" }