Pass coredata to ViewController based on cell selection - ios

Question

I need to present a new ViewController when selecting a UICollectionView Cell and pass the data from the entity used to fill selected cell.
Here is the code used to fill cell data:
let pets = PersistenceManager.shared.fetch(Pet.self)
var _fetchResultsController: NSFetchedResultsController <Pet>?
var fetchResultsController: NSFetchedResultsController <Pet>?{
get{
if _fetchResultsController == nil {
let moc = PersistenceManager.shared.context
moc.performAndWait {
let fetchRequest = PersistenceManager.shared.petsFetchRequest()
_fetchResultsController = NSFetchedResultsController.init(fetchRequest: fetchRequest, managedObjectContext: moc, sectionNameKeyPath: nil, cacheName: nil) as? NSFetchedResultsController<Pet>
_fetchResultsController?.delegate = self
do {
try self._fetchResultsController?.performFetch()
}catch {
}
}
}
return _fetchResultsController
}
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionViewHorizontal.dequeueReusableCell(withReuseIdentifier: "HorCell", for: indexPath) as! PRMainHorizontalCollectionViewCell
if let pet= self.fetchResultsController?.fetchedObjects, indexPath.row < pet.count{
let _pet= fetchResultsController!.object(at: indexPath)
// cell UI goes here
}
return cell
}
I understand I need to use didSelectItemAt, I just don't know what information needs to go in the function. Please let me know of anything else needed to better help answer this question. Thank you.
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
// Added the line below based on karthik's answer. But I am unsure how to implement it.
let selectedObj = fetchResultsController!.object(at: indexPath)
let vc = self.storyboard?.instantiateViewController(withIdentifier: "selectedPetViewController") as! PRSelectedPetViewController
navigationController?.pushViewController(vc, animated: true)
}

Answer 1

I prefer the following architecture:
This is the main controller with data.
For a better understanding, I will simplify the data source.
class ViewController: UIViewController {
// code ...
#IBOutlet var collectionView: UICollectionView!
fileprivate var data = [Pet]()
}
extension ViewController: UICollectionViewDataSource {
// code ...
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return data.count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
guard let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "HorCell", for: indexPath) as? PRMainHorizontalCollectionViewCell else {
return UICollectionViewCell()
}
let pet = data[indexPath.row]
// TODO: configure cell using pet ...
return cell
}
}
extension ViewController: UICollectionViewDelegate {
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
let row = indexPath.row
let pet = data[row]
// TODO: Get the child controller in any way convenient for you.
let childController = ChildViewController()
// With the help of the delegate, we will receive notification of changes pet.
childController.delegate = self
// Thus, we pass the data to the child controller.
childController.pet = pet
childController.indexPath = indexPath
// TODO: Present the view controller in any way convinient for you.
}
}
extension ViewController: ChildViewControllerDelegate {
func saveButtonPressed(_ controller: ChildViewController) {
guard let pet = controller.pet, let indexPath = controller.indexPath else {
return
}
// We save data and reload the cell whose data we changed.
self.data[indexPath.row] = pet
collectionView.reloadItems(at: [indexPath])
}
func cancelButtonPressed(_ controller: ChildViewController) {
// Do something if necessary...
}
}
In addition to the controller, the child controller also provides a delegate protocol for notification of changes.
protocol ChildViewControllerDelegate {
func saveButtonPressed(_ controller: ChildViewController)
func cancelButtonPressed(_ controller: ChildViewController)
}
// This is the controller you want to show after selecting a cell.
// I assume that in the child controller there is a button to save and cancel.
class ChildViewController: UIViewController {
var delegate: ChildViewControllerDelegate?
// The object whose data we are editing in the controller.
var pet: Pet!
// The location of the object in the main controller.
var indexPath: IndexPath!
override func viewDidLoad() {
// TODO: Configure user interface using self.pet
}
#IBAction func saveButtonPressed(_ button: UIButton) {
delegate?.saveButtonPressed(self)
}
#IBAction func cancelButtonPressed(_ button: UIButton) {
delegate?.cancelButtonPressed(self)
}
}

Answer 2

you can follow this to pass information to another view controller.
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
let selectedObj = fetchResultsController!.object(at: indexPath)
// instantiate presenting view controller object
// add one property (manange object) in your presenting viewcontroller
// assign the selected object to that property
// present the view controller
}