Is there a way to update an object in a core data model by pressing bar button item? - swift

Question

My goal here is to update an object in my core data by pressing the done button after editing the text.
The done button and the textfields below:
Here is some of my code,
#objc func doneTapped() {
do {
try context.save()
} catch {
print("Error saving the new information \(error)")
}
dateEditableTextF.resignFirstResponder()
selectedEventDate = dateEditableTextF.text
dateEditableTextF.isEnabled = false
costEditableTextF.resignFirstResponder()
selectedEventCost = costEditableTextF.text
costEditableTextF.isEnabled = false
gradesEditableTextF.resignFirstResponder()
selectedEventGrade = gradesEditableTextF.text
gradesEditableTextF.isEnabled = false
navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: .edit, target: self, action: #selector(editTapped))
}
I expected that when I pressed the done button while running the app after editing the textfields, the information would update and that when I went back to the view controller, the information would be the same and my core data database would be update with an update attribute for that object.
What actually happened was when I finish editing the textfield, the data updates in the view controller, but when I leave the view controller and come back to it, the data reverts to the old entry.
I watched about 4 youtube videos of crud methods and they all were different scenarios and didn't match mine so I was hoping someone here could help. Thanks in advance.
Here's the rest of my view controller.
#IBOutlet weak var costEditableTextF: UITextField!
#IBOutlet weak var dateEditableTextF: UITextField!
#IBOutlet weak var gradesEditableTextF: UITextField!
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
var updateTheEvents = [Event]()
var selectedEventName: String?
var selectedEventDate: String?
var selectedEventCost: String?
var selectedEventGrade: String?
override func viewDidLoad() {
super.viewDidLoad()
navigationItem.title = selectedEventName
navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: .edit, target: self, action: #selector(editTapped))
if let dateToLoad = selectedEventDate {
dateEditableTextF.text = selectedEventDate
}
if let costToLoad = selectedEventCost {
costEditableTextF.text = selectedEventCost
}
if let gradesToLoad = selectedEventGrade {
gradesEditableTextF.text = selectedEventGrade
}
// Do any additional setup after loading the view.
}
#objc func editTapped() {
dateEditableTextF.becomeFirstResponder()
dateEditableTextF.isEnabled = true
costEditableTextF.isEnabled = true
gradesEditableTextF.isEnabled = true
navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: .done, target: self, action: #selector(doneTapped))
}

Answer 1

First you need to create a storage to manage your persistentContainer and the CRUD operations:
class PersistenceManager {
lazy var persistentContainer: NSPersistentContainer = {
let container = NSPersistentContainer(name: "your_xcdatamodeld_name") //Here you should type the name of your xcdatamodeld file without the extension .xcdatamodeld
container.loadPersistentStores(completionHandler: { (storeDescription, error) in
if let error = error as NSError? {
fatalError("Unresolved error \(error), \(error.userInfo)")
}
})
container.viewContext.automaticallyMergesChangesFromParent = true
container.viewContext.mergePolicy = NSMergeByPropertyStoreTrumpMergePolicy
return container
}()
}
Now to save data, you'll need a context. I strongly suggest that you use a global one. I had several issues accessing the store context from external functions (ie. stuff wasn't added/edited). Note that, despite it works great for me, I'm not sure wether a global context is the best practice. I have encountered any issues yet, however.
Inside of your PersistenceManager class, before the persistentContainer put the following code
static let shared = PersistenceManager()
var managedObjectContext: NSManagedObjectContext {
persistentContainer.viewContext
}
And, before and outside of the class put the following
let context = PersistenceManager.shared.managedObjectContext
...
class PersistenceManager { [...] }
Now you'll have to create your saving function like this:
func saveContext () {
if context.hasChanges {
do {
try context.save()
} catch {
let nserror = error as NSError
fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
}
}
This goes inside of the PersistenceManager class.
Now comes the fun part: You'll have to create the CRUD functions. These will all be inside of your PersistenceManager class. I'm going to show you a small demonstration about creating and editing entities.
Let's assume you have an entity named "Item" and it has the attributes name and price.
To save each item, you'll have a function like the following one:
func creaateNewItem(name: String, price: Int) -> Item {
let entity = NSEntityDescription.entity(forEntityName: Item, in: context)
let newItem = Item(entity: entity!, insertInto: context)
newItem.name = name
newItem.price = price
self.saveContext()
return newItem
}
To edit the item, you'll have to fetch it and then assign it the new values:
func editItem(currentItem: Item, newName: String, newPrice: Int) {
let currentName: String = currentItem.name! //Current name
//Looking for the item to edit
let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Item")
request.predicate = NSPredicate(format: "name = %#", currentName)
request.returnsObjectsAsFaults = false
do { //Editing the item
let editedItem = (try context.fetch(request))[0] as! Item
editedItem.name = newName
editedItem.price = newPrice
self.saveContext()
} catch let error {
print("Error \n \((error))")
}
}
As you see here I passed some parameters which will allow you to customise your Items. Obviously if you need to assign default values you can remove those parameters.
Now, in your view controller, you'll create an Item array object:
my item : [Item]?
Which will be filled with your items.
To edit your saved items by pressing a bar button you'll now simply have to do the following:
#objc func editMyItem(){
let newName = "Edited Item"
let newPrice = 15
PersistenceManager().editItem(currentItem: item[indexOfYourChoice], newName: newName, newPrice: newPrice)
}
And your item will be edited!
Note that if you want the text to come from a textfield the newPrice constant will be equal to that textfield's text, for instance.