Welcome to the Treehouse Community

The Treehouse Community is a meeting place for developers, designers, and programmers of all backgrounds and skill levels to get support. Collaborate here on code errors or bugs that you need feedback on, or asking for an extra set of eyes on your latest project. Join thousands of Treehouse students and alumni in the community today. (Note: Only Treehouse students can comment or ask questions, but non-students are welcome to browse our conversations.)

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and a supportive community. Start your free trial today.

iOS Introduction to Table Views Displaying Contact Data Lists of Contacts

Peter Correa
Peter Correa
17,155 Points

Can someone explain the following code?

I understand that the code is intializing the Contacts struct. However I need clarification on what's going on inside the init? method, more specificaly the use of the subscripts with the parameter "dictionary."

struct Contact {
    let firstName: String
    let lastName: String
    let phone: String
    let email: String
    let street: String
    let city: String
    let state: String
    let zip: String
    let image: UIImage?
    var isFavorite: Bool

extension Contact {

    struct Key {
        static let firstName = "firstName"
        static let lastName = "lastName"
        static let phone = "phoneNumber"
        static let email = "email"
        static let street = "streetAddress"
        static let city = "city"
        static let state = "state"
        static let zip = "zip"
        static let image = "avatarName"

//this is where I am stuck...
    init?(dictionary: [String: String]) {
        guard let firstNameString = dictionary[Key.firstName],
            let lastNameString = dictionary[Key.lastName],
            let phoneString = dictionary[Key.phone],
            let emailString = dictionary[Key.email],
            let streetString = dictionary[Key.street],
            let cityString = dictionary[Key.city],
            let stateString = dictionary[Key.state],
            let zipString = dictionary[Key.zip] else { return nil }

        self.firstName = firstNameString
        self.lastName = lastNameString
        self.phone = phoneString
        self.email = emailString
        self.street = streetString
        self.city = cityString
        self.state = stateString
        self.zip = zipString

        if let imageName = dictionary[Key.image] {
            self.image = UIImage(named: imageName)
        } else {
            image = nil

        isFavorite = false

1 Answer

Jhoan Arango
Jhoan Arango
14,522 Points


It's simple really, the init is a fail-able initializer, that takes a dictionary as its parameter. So inside of it, you have a guard that if any of the information is missing, it will fail to initialize the struct.

// We have a dictionary
let someCarDictionary: [String : String] = ["fiesta" : "Ford Fiesta" , "mustang" : "Ford Mustang"]

// This is how we retrieve a value from a dictionary, by passing it the key. ( Key Value )
let car = someCarDictionary["fiesta"] 
print(car) // Will print "Ford Fiesta"

So in the init, all it's doing is passing keys for the respective value to be able to initialize all its properties.

Hope that helps you a bit.

If you need a more detail answer let me know.

Good luck

Peter Correa
Peter Correa
17,155 Points

Thanks Jhoan! Really helped!