Find the indexPath in ViewController - ios

Question

I segued to a new View Controller. This view controller contains array data from the corresponding CollectionViewCell. How do I change the data to present the previous cell array? Without having to go back to the last view controller and selecting the cell from there? I'm using Swift 3 Below is an image that explains what I mean
The first image is in the first View Controller. The second and third images are what's displayed when either of the first two in the list are tapped. You can go to the next index using the arrow keys in the second View Controller. How do I achieve this functionality?
let dataSource = DataSource()
func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int {
return 1
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
if inSearchMode {
return filteredAnimal.count
}
return dataSource.anim.filter{ $0.isDefault! }.count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "AnimIndex", for: indexPath as IndexPath) as! AnimIndex
let animal: Animal
if inSearchMode {
animal = filteredAnimal[indexPath.row]
} else {
animal = dataSource.anim.filter{ $0.isDefault! }[indexPath.row]
}
cell.configureCell(animal)
return cell
}

Answer 1

This is a very common UI pattern. You should search on master/detail. You should be able to find lots of sample projects that give examples of this UI pattern.
Don't think in terms of cells. Think in terms of a model object - a store for your app data. You need a model object that represents the entire list of data you present in your first view controller.
That model object should be reachable from all view controllers that need to display information from it. You can either pass around a reference to the model object or make it a singleton. There are advantages to either approach.
For collection views and table views, which are organized by section and row, an array of arrays of data objects is often a good structure for your model. If your data is in a single section then you can use a single array.
When the user taps on a cell in your first view controller, you would invoke the second view controller (Either from a segue or by manually invoking it.) You'd pass the second view controller the indexPath of the selected object, and might also pass a reference to your model object (or, like I said, you could make the model object a globally accessable singleton, in which case you wouldn't need to pass it.)
Then, in the second (or 3rd) view controller, if the user taps the up/down button, you have access to the model object that stores ALL the data your app is presenting, so you can navigate to the next object from within any view controller. If your data is organzied in sections and rows or rows and columns you might want to add next/previous item methods to your data model so you only have to write that logic once.