changing existing data in viewcontroller between view controllers with self.dismiss

Question

I have a view controller. That does a Modal present Segue of a full screen view controller. It passes the image data list to the full screen view controller. This list has properties associated with it such as likes, views, etc. I have looked at ther answers, but believe they will completely replace the current array, which I think will completely reload every bit of data that is cashed on the first view. So I only want to modify data that needs to be modified.

Class FirstController {
    var photosList: [customStruct] = [Photo1,Photo2,Photo3] 
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "photofull" {

        if let fullImaageViewController = segue.destination as? ImageDetailViewController {
            fullImageViewController.photosList = photosList
        }
    }
}

here the data is passed forward through a Modal view controller. In the full imageViewcontroller, the data, such as like can be altered. [photosList[1].imageLikes = photosList[1].imageLikes+1

The only problem I am only able to change this data on the fullImageViewController, not in the FirstController. is there a way to access it on the previous one too?

I would like to do something like FirstController().[photosList[1].imageLikes = FirstController.photosList[1].imageLikes+1 which doesn't work.

Answer 1

Well, what you need here is a simple delegate protocol to transfer data from one ViewController to another ViewController.

Below are the steps how to work with protocol.

In ViewController2 or fullImaageViewController do the following steps.

Just above your class declaration declare your delegate.

protocol MyDelegate:class { // declare your protocol a class protocol
    func sendDataBack(value: Photo)
}

In class declare a variable of your delegate

weak var myDelegateObj: MyDelegate? // always declare a weak delegate so that it cannot capture the memory of the object

and when you dismiss the VC just call the delegate with line

myDelegateObj?.sendDataBack(value: Photo)

---

Now go to your FirstViewController and go to the line where you have declared the FirstViewController Obj if not declare it either in viewdidload or when you presenting your view. and do the following.

let vc = FirstViewController()
vc.myDelegateObj = self

and implement the method your delegate in the FirstViewController

In FirstViewController:

make your firstView conform to MyDelegate Protocol by doing:

class FirstViewController: UIViewController,MyDelegate

and Implement the MyDelegate Method

// update only altered photo
func sendDataBack(value: Photo) {
    if let index = photosList.index(where: {$0.imageID == Photo.imageID}){
        PhotoList[index] = Photo
    }
 }

And then before the initial segue, I use

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "photofull" {
        if let fullImaageViewController = segue.destination as? ViewController2 {
            fullImaageViewController.myDelegateObj = self
        }
    }
}

Hope this helps.