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iOS

Posted by Brandon Mahoney
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Brandon Mahoney
iOS Development with Swift Techdegree Graduate 30,149 Points

Describe use of ??

I had some recent code which I had some issues with. I was getting the error: Cannot subscript value of type 'String' with an index of type 'NSIndexPath'

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        let wod = FilteredWodList[index]
        if segue.identifier == "showBenchmarkDetail" {
            let controller = segue.destinationViewController as? BenchmarkWODDetailView
            if let indexPath = self.tableView.indexPathForSelectedRow

            {
            controller?.nameText = wod.name![indexPath]
            controller?.descriptionText = wod.description![indexPath]
            controller?.exerciseText = wod.exercise![indexPath]
            }

The following change using '??' corrected the problem.

    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {

        if segue.identifier == "showBenchmarkDetail" {
            let controller = segue.destinationViewController as? BenchmarkWODDetailView
            if let indexPath = self.tableView.indexPathForSelectedRow

            {


                let wod = FilteredWodList[indexPath.row]
                controller?.nameText = wod.name ?? ""
                controller?.descriptionText = wod.description ?? ""
                controller?.exerciseText = wod.exercise ?? ""
            }

Can someone please describe to me why this corrects the problem.

1 Answer

AR Ehsan
AR Ehsan
7,912 Points
AR Ehsan
AR Ehsan
7,912 Points

So technically what's going on here is that it's checking if wod.description is not nil, it will return wod.description. If it's nil, it will return "" (empty strings).