This post is part of my collection: Swift 2 – For Beginners.

Swift extensions add new functionality to an existing class, structure, enumeration, or protocol type.

In this example we will see how to write a UIViewController extension to show loading indicators and alerts.

To add a class extensions we have to write something like:

extension UIViewController {
// write your extensions here
}

Show a loading indicator

Our first extension method will be a method that should show a loading indicator and disable the application so that the user cannot interact with it. To help the user understand that the application is disabled it should be grayed out.

To use this method we don’t need any parameter but we need a reference to the created indicator to hide it later:

var spinner = self.showModalSpinner()

To do this we can use the class UIActivityIndicatorView.

/**
Shows a loading indicator and disables user interaction with the app until it is hidden
*/
func showModalSpinner() ->UIActivityIndicatorView{

// user cannot interact with the app while the spinner is visible
UIApplication.sharedApplication().beginIgnoringInteractionEvents()

var indicator = UIActivityIndicatorView()

indicator = UIActivityIndicatorView(frame: self.view.frame)
indicator.center = self.view.center
indicator.backgroundColor = UIColor(white: 0.0, alpha: 0.5)
indicator.activityIndicatorViewStyle = UIActivityIndicatorViewStyle.Gray
indicator.hidesWhenStopped = true
indicator.startAnimating()

self.view.addSubview(indicator)

return indicator
}

Now we need a method to hide the spinner when our task was completed:

self.hideModalSpinner(self.spinnerView)

/**
Hides the loading indicator and enables user interaction with the app
*/
func hideModalSpinner(indicator: UIActivityIndicatorView){

indicator.stopAnimating()
indicator.hidden = true

// user can interact again with the app
UIApplication.sharedApplication().endIgnoringInteractionEvents()
}

If we put these two methods within a UIViewController extension we can use them like a normal method of the class.

Show an alert

Let’s add now a method to our extension to show an alert to the user, it should have an ‘ok’ button that will close the alert when the user taps it.

I would like to have a very simple method that has only two parameters to indicate the title and message:

self.showAlert("Error", message: "Invalid user name / password.")

We can use the class UIAlertController to do that:

/**
Shows an alert with a title and a message
*/
func showAlert(title: String, message:String) {

let alertController = UIAlertController(title: title, message: message, preferredStyle: UIAlertControllerStyle.Alert)

// show the alert with a "ok" button that will close the alert
let okAction = UIAlertAction(title: "ok", style: UIAlertActionStyle.Default) { (action) -> Void in
self.dismissViewControllerAnimated(true, completion: nil)
}
alertController.addAction(okAction)

// show alert controller
self.presentViewController(alertController, animated: true, completion: nil)
}

Complete example:

import UIKit
extension UIViewController{

/**
Shows an alert with a title and a message
*/
func showAlert(title: String, message:String) {

let alertController = UIAlertController(title: title, message: message, preferredStyle: UIAlertControllerStyle.Alert)

// show the alert with a "ok" button that will close the alert
let okAction = UIAlertAction(title: "ok", style: UIAlertActionStyle.Default) { (action)-> Void in
self.dismissViewControllerAnimated(true, completion: nil)
}
alertController.addAction(okAction)

// show alert controller
self.presentViewController(alertController, animated: true, completion: nil)
}

/**
Shows a loading indicator and disables user interaction with the app until it is hidden
*/
func showModalSpinner()->UIActivityIndicatorView{

// user cannot interact with the app while the spinner is visible
UIApplication.sharedApplication().beginIgnoringInteractionEvents()

var indicator = UIActivityIndicatorView()

indicator = UIActivityIndicatorView(frame: self.view.frame)
indicator.center = self.view.center
indicator.backgroundColor = UIColor(white: 0.0, alpha: 0.5)
indicator.activityIndicatorViewStyle = UIActivityIndicatorViewStyle.Gray
indicator.hidesWhenStopped = true
indicator.startAnimating()

self.view.addSubview(indicator)

return indicator
}

/**
Hides the loading indicator and enables user interaction with the app
*/
func hideModalSpinner(indicator: UIActivityIndicatorView){

indicator.stopAnimating()
indicator.hidden = true

// user can interact again with the app
UIApplication.sharedApplication().endIgnoringInteractionEvents()
}
}

This post is part of my collection: Swift 2 – For Beginners.

JSON (JavaScript Object Notation) is a lightweight, human readable, open source, data-interchange format. In this example we will see how to serialize and deserialize objects to/from JSON using ObjectMapper in our iOS application.

For example, this would be the JSON representation of an object with two properties
name: string = “Juan Carlos”
age: Int = 29

ObjectMapper is an open source project to make JSON Object mapping written in Swift. It is available in github: ObjectMapper.

Reference ObjectMapper using CocoaPods

CocoaPods is a dependency manager for Swift and Objective-C Cocoa projects. We will use it to reference ObjectMapper in our project. (If would also be possible to add it as a submodule. Check the project in GitHub for more information)

To add ObjectMapper to our project we need to execute the following commands:
Install cocoapods

sudo gem install cocoapods

Create Podfile in our project root

touch Podfile

To reference ObjectMapper add this content to the PodFile

use_frameworks!
pod 'ObjectMapper', '~> 1.0'

Select XCode path

sudo xcode-select --switch /Applications/Xcode.app

Add ObjectMapper repository

pod repo add ObjectMapper https://github.com/Hearst-DD/ObjectMapper.git

Install the project locally

pod install

Close XCode and open the created file *.xcworkspace. It contains our project and a reference to a new project called Pods. All our referenced projects will be contained in this new project.

Now we are ready to import and use ObjectMapper:

import ObjectMapper

Define our objects and implement the protocol “Mappeable”

To serialize and deserialize objects we must implement the protocol Mappeable.

// Mappeable source code
public protocol Mappable {
	init?(_ map: Map)
	mutating func mapping(map: Map)
}

Let’s write our User class, it will have two properties, name and age. The class will also implement the protocol Mappeable.

// Define our class and implement the Mappable protocol
class User: Mappable {
    var name: String?
    var age: Int = 0
    
    init(name: String, age: Int) {
        self.name = name
        self.age = age
    }
    
    // MARK: Mappable
    required init?(_ map: Map) {
        // subClasses must call the constructor of the base class
        // super.init(map)
    }

    func mapping(map: Map) {
        name <- map["name"]
        age  <- map["age"]
    }
}

Serialize and Deserialize objects

ObjectMapper is extremely easy to use:

        // Object to be serialized to JSON
        let myUser = User(name: "Juan Carlos", age: 29)

        // Convert Object to JSON
        let serializedUser = Mapper().toJSONString(myUser)
        print(serializedUser)
        
        // Convert JSON to Object
        if let deserializedUser = Mapper<User>().map(serializedUser){
            print(deserializedUser.name)
        }
        
        // Output:
        //  Optional("{\"age\":29,\"name\":\"Juan Carlos\"}")
        //  Optional("Juan Carlos")

This post is part of my collection: Swift 2 – For Beginners.

Core Data is a persistence framework provided by Apple. In this example we will see how to use it in our iOS application. First we will see how to create our data model and then how to perform the following basic operations:

• Create
• Get by Id
• Get all and Get applying a predicate
• Update
• Remove

How to create our data model

A data model consist of a group of entities. The concept of entity in Core Data is similar to the concept of table in SQL. Each entity can have attributes in the same way that a table can have columns.

To create a new entity you need a project with Core Data included. Then go to your xdatamodel file and click “Add Entity”, “Add Attribute” to configure it.

To keep the example simple our data model will have one entity with two attributes. A Person with name and age:

Person
-name: string
-age: integer

To create a class that represent our data model click on “Editor” > “Create NSManagedObject Subclass…”.

It should create a class and an extension representing our entity “Person”. To that class we will only add a static field with the entity name, we will use it later to avoid magic strings:

extension Person {
    @NSManaged var name: String?
    @NSManaged var age: NSNumber?
}

class Person: NSManagedObject {
    // Add this line, the string must be equal to your class name
    static let entityName = "Person"
}

managedObjectContext

Before writing code to make our basic operations it is important to know what the managedObjectContext is.

When the project has Core Data Xcode add a bunch of code to our AppDelegate.swift. A piece of that code is the managedObjectContext. This is the object that we need to access the data model. We can get it in our controller with this line of code:

let context = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext

To save our changes we always have to call context.save(). It can throw an exception so we have to make the call in a do.. catch.. block:

    // Saves all changes
    func saveChanges(){
        do{
            try context.save()
        } catch let error as NSError {
            // failure
            print(error)
        }
    }

Now we are ready to write our basic functions to access the data model:

Create

    // Creates a new Person
    func create(name: String, age: NSNumber) -> Person {
        
        let newItem = NSEntityDescription.insertNewObjectForEntityForName(Person.entityName, inManagedObjectContext: context) as! Person
        
        newItem.name = name
        newItem.age = age
        
        return newItem
    }

GetById

    // Gets a person by id
    func getById(id: NSManagedObjectID) -> Person? {
        return context.objectWithID(id) as? Person
    }

Get

Now we will see how to get all entities and how to get all entities applying a NSPredicate to our query.

    // Gets all with an specified predicate.
    // Predicates examples:
    // - NSPredicate(format: "name == %@", "Juan Carlos")
    // - NSPredicate(format: "name contains %@", "Juan")
    func get(withPredicate queryPredicate: NSPredicate) -> [Person]{
        let fetchRequest = NSFetchRequest(entityName: Person.entityName)
        
        fetchRequest.predicate = queryPredicate
        
        do {
            let response = try context.executeFetchRequest(fetchRequest)
            return response as! [Person]
            
        } catch let error as NSError {
            // failure
            print(error)
            return [Person]()
        }
    }

Our get all function will be a call to the previous function. The predicate will be a true predicate, to return all objects in our data model.

    // Gets all.
    func getAll() -> [Person]{
        return get(withPredicate: NSPredicate(value:true))
    }

Update

    // Updates a person
    func update(updatedPerson: Person){
        if let person = getById(updatedPerson.objectID){
            person.name = updatedPerson.name
            person.age = updatedPerson.age
        }
    }

Remove

    // Deletes a person
    func delete(id: NSManagedObjectID){
        if let personToDelete = getById(id){
            context.deleteObject(personToDelete)
        }
    }

Complete example:

This class puts all the functions that we have seen before together, we can call it PersonService.

import CoreData

class PersonService{
    
    var context: NSManagedObjectContext
    
    init(context: NSManagedObjectContext){
        self.context = context
    }
    
    // Creates a new Person
    func create(name: String, age: NSNumber) -> Person {
        
        let newItem = NSEntityDescription.insertNewObjectForEntityForName(Person.entityName, inManagedObjectContext: context) as! Person
        
        newItem.name = name
        newItem.age = age
        
        return newItem
    }
    
    // Gets a person by id
    func getById(id: NSManagedObjectID) -> Person? {
        return context.objectWithID(id) as? Person
    }
    
    // Gets all.
    func getAll() -> [Person]{
        return get(withPredicate: NSPredicate(value:true))
    }
    
    // Gets all that fulfill the specified predicate.
    // Predicates examples:
    // - NSPredicate(format: "name == %@", "Juan Carlos")
    // - NSPredicate(format: "name contains %@", "Juan")
    func get(withPredicate queryPredicate: NSPredicate) -> [Person]{
        let fetchRequest = NSFetchRequest(entityName: Person.entityName)
        
        fetchRequest.predicate = queryPredicate
        
        do {
            let response = try context.executeFetchRequest(fetchRequest)
            return response as! [Person]
            
        } catch let error as NSError {
            // failure
            print(error)
            return [Person]()
        }
    }
    
    // Updates a person
    func update(updatedPerson: Person){
        if let person = getById(updatedPerson.objectID){
            person.name = updatedPerson.name
            person.age = updatedPerson.age
        }
    }
    
    // Deletes a person
    func delete(id: NSManagedObjectID){
        if let personToDelete = getById(id){
            context.deleteObject(personToDelete)
        }
    }
    
    // Saves all changes
    func saveChanges(){
        do{
            try context.save()
        } catch let error as NSError {
            // failure
            print(error)
        }
    }
}

How to use the service:

        // Create an instance of the service.
        let context = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext
        let personService = PersonService(context: context)
        
        // Create
        let juanCarlos = personService.create("Juan Carlos", age: 52)

        // Read all
        var people : [Person] = personService.getAll()

        // Read by id
        let firstPerson = personService.getById(people[0].objectID)!

        // Update
        firstPerson.name = "Juan Carlos Sanchez"
        personService.update(firstPerson)

        // Delete
        personService.delete(firstPerson.objectID)