Core data is a framework that is used to save data in iOS app development and OS X platform. Today we’ll develop an application using SWIFT programming language that will have a textfield, a button and a textview that will save and display data fetched from Core Data. To learn more about Core-Data please visit:
Introduction to Core Data Programming Guide
Summary:
Step 1: Create Project
Step 2: Design Core-Data database
Step 3: Write script to save and fetch data from core data.
Step 1:
1. Create a new project in Xcode. In first window of the wizard select Single view application. In next screen, select SWIFT from dropdown box and also check “Use Core Data” checkbox (bottom of the wizard). Please use “NotePad” as your project name.
2. Open Main.storyboard and add a textfield, a button. Below the button add big textview. ( Note: textfield is for one line. For multiple lines use textview).
Step 2:
1. Now, open NotePad.xcdatamodeld (YourProjectName.xcdatamodeld). This is the place where you design your database.
2. Here you add Entity (Entity is similar to Table of Oracle / MySql database, but not exactly). At the bottom of the page, you will see Add Entity button (1). Click on it. New entity (2) will be added. By double clicking on it, you can change it’s name. I changed it to “Note”
3. Now select the entity (if it’s not already selected). Add “Attribute” to it by clicking + button (3) below the Attributes section. Attribute is similar to column of a table. For each attribute we should select a type from dropdown box. I’m using only one attribute “paper” with type “String”.
4. At this point you have to do an important thing. In Utilities panel (Right side bar), you will see a box labeled: “Class” (4) in entity section. Write here : NotePad.Note; Actually, it should be ApplicationName.EntityName
5. Now we’ll generate Entity Classes. To do this, go to Editor > Create NSManagedObjectSubclass. Select the data model (It’s the file name that we have worked on). In next screen, select Entity name. We’ve only one Entity. Click next. Now, you will see a dialog box for saving entity file. Here, from language dropdown box select swift and finally click Create button.
Step 3:
1. Add outlets to textField and textview.
2. Add IBAction to button. You can also rename the button to “Add”
3. Open ViewController.swift.
We’ll edit this file. Before we proceed, let me give you an example. Suppose we have some food, one tray and a refrigerator. To save the food, we’ve to put it on the tray and keep the tray inside refrigerator. Saving method of Core data is similar. Here data is food, managedObject is tray and managedObject.save is equivalent to keeping tray contained food inside refrigerator.
First import CoreData in your viewController
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import CoreData |
declare an array NSManagedObject below IBOutlet declaration. so the code will look like this:
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import UIKit import CoreData class ViewController: UIViewController { //-- Declare Outlets --// @IBOutlet weak var textFieldNote: UITextField! @IBOutlet weak var textViewAllNotes: UITextView! //-- declare allPapers variables // it will contain all data fetched from core data --// var allPapers = [NSManagedObject]() } |
To fetch data from CoreData we can use following method:
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//-- fetch data from CoreData --// func fetchPapers () { //-- CoreData starts --// let appDelegate = UIApplication.sharedApplication().delegate as AppDelegate var managedObjectContext = appDelegate.managedObjectContext! let fetchRequest = NSFetchRequest(entityName: "Note") var error: NSError? let fetchResults = managedObjectContext.executeFetchRequest(fetchRequest, error: &error) as [NSManagedObject]? if let results = fetchResults { allPapers = results } else { println("Not fetched\(error), \(error!.userInfo)") } //-- CoreData ends --// var textToDisplay = "" for paper in allPapers { textToDisplay += paper.valueForKey("paper") as String textToDisplay += "\n" } textViewAllNotes.text = textToDisplay } |
Above method fetches all data in Note entity. At the end of the method, we used for loop to get each text inside paper and add them in a local variable. finally show all texts in large text view.
To save data in Core data use following code. We are saving text in paper attribute (column) of Note entity (table)
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//-- Save to CoreData --// func saveNote(myText:String){ //-- Get a tray first --// let appDelegate = UIApplication.sharedApplication().delegate as AppDelegate let managedObjectContext = appDelegate.managedObjectContext! let entity = NSEntityDescription.entityForName("Note", inManagedObjectContext: managedObjectContext) let paper = NSManagedObject(entity: entity!, insertIntoManagedObjectContext: managedObjectContext) //-- put food on tray --// paper.setValue(myText, forKey: "paper") allPapers.append(paper) var error: NSError? //-- put the tray inside refrigerator --// if managedObjectContext.save(&error) { println("Couldn't save\(error?.userInfo)") } fetchPapers() } |
Now implement saveNote in IBAction actionAddNote. Clear the text field so that you can add new note.
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@IBAction func actionAddNote(sender: AnyObject) { var myText = textFieldNote?.text saveNote(myText!) textFieldNote.text = "" } |
Full source code of ViewController.swift. You can also download the whole project from the link provided at the end this tutorial.
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import UIKit //-- Import CoreData --// import CoreData class ViewController: UIViewController { //-- Declare Outlets --// @IBOutlet weak var textFieldNote: UITextField! @IBOutlet weak var textViewAllNotes: UITextView! //-- declare allPapers variables // it will contain all data fetched from core data --// var allPapers = [NSManagedObject]() override func viewDidLoad() { super.viewDidLoad() } override func viewWillAppear(animated: Bool) { fetchPapers() } //-- fetch data from CoreData --// func fetchPapers () { //-- CoreData starts --// let appDelegate = UIApplication.sharedApplication().delegate as AppDelegate var managedObjectContext = appDelegate.managedObjectContext! let fetchRequest = NSFetchRequest(entityName: "Note") var error: NSError? let fetchResults = managedObjectContext.executeFetchRequest(fetchRequest, error: &error) as [NSManagedObject]? if let results = fetchResults { allPapers = results } else { println("Not fetched\(error), \(error!.userInfo)") } //-- CoreData ends --// var textToDisplay = "" for paper in allPapers { textToDisplay += paper.valueForKey("paper") as String textToDisplay += "\n" } textViewAllNotes.text = textToDisplay } override func didReceiveMemoryWarning() { super.didReceiveMemoryWarning() // Dispose of any resources that can be recreated. } @IBAction func actionAddNote(sender: AnyObject) { var myText = textFieldNote?.text saveNote(myText!) textFieldNote.text = "" } //-- Save to CoreData --// func saveNote(myText:String){ //-- Get a tray first --// let appDelegate = UIApplication.sharedApplication().delegate as AppDelegate let managedObjectContext = appDelegate.managedObjectContext! let entity = NSEntityDescription.entityForName("Note", inManagedObjectContext: managedObjectContext) let paper = NSManagedObject(entity: entity!, insertIntoManagedObjectContext: managedObjectContext) //-- put food on tray --// paper.setValue(myText, forKey: "paper") allPapers.append(paper) var error: NSError? //-- put the tray inside refrigerator --// if managedObjectContext.save(&error) { println("Couldn't save\(error?.userInfo)") } fetchPapers() } } |
You can download the whole project by clicking here.