PJ-09-UserDefaults.md

User Defaults

Code related: Projects/UserDefaults

What you learn

• How to save data using UserDefaults
• How to retrieve data from UserDefaults
• Generic approach for user defaults

Initial setup

You must use the UserDefaults Starter for this module. Inside the starter project you should have the project structure used on the LoginForm project

Easy way to save and retrieve data

1. Bind label outlet

2. Store a message

In order to save a string, just add the next line:

UserDefaults.standard.set("Are you ready?", forKey: "LoadingMessage")

Note: You need to be aware that you have access to multiple methods for store data:

• integer(forKey:) returns an integer if the key existed, or 0 if not.
• bool(forKey:) returns a boolean if the key existed, or false if not.
• float(forKey:) returns a float if the key existed, or 0.0 if not.
• double(forKey:) returns a double if the key existed, or 0.0 if not.

3. Retrieve a message

After saving a custom welcome message, we need to retrieve it from user defaults:

let loadingMessage = UserDefaults.standard.string(forKey: "LoadingMessage")

3. Use the stored message value

Now we can use the stored value to display the the message on our message label.

messageLabel.text = loadingMessage

At the end your code should look like this:

import UIKit

class DispatchViewController: UIViewController {

    private let mainFlow: Flow = .login

    @IBOutlet weak var messageLabel: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()

        UserDefaults.standard.set("Are you ready?", forKey: "LoadingMessage")
        let loadingMessage = UserDefaults.standard.string(forKey: "LoadingMessage")

        messageLabel.text = loadingMessage

        DispatchQueue.main.asyncAfter(deadline: .now() + 2) {
            self.setMainFlow(to: self.mainFlow)
        }
    }

}

Local folder setup

At this point we are ready to create an structured way for using user defaults. First we need to add the Local folder to our project:

1. Add a new Local folder inside the Data folder using Finder
2. Add new files to our UserDefaults project inside the Xcode

Structured way to save and retrieve data

Inside our folder Data/Local we need to create an enum to keep track of all our keys, named LocalKeys.swift, use the following structure:

enum LocalKeys: String {
    case loadingMessage = "loading-message"
}

Note: In the future you may end up using a structure like this:

enum LocalKeys: String {
    enum User: String {
        case current = "user-current"
    }

    enum Token: String {
        case authToken = "token-auth"
    }

    //HERE: Add your custom keys
}

Now, also inside our folder Data/Local the next file to create is a protocol to define our local data manager behavior. The file name should be DispatchManagerProtocol.swift.

protocol DispatchManagerProtocol {
    func save(message: String?)
    func retrieve() -> String?
    func clear()
}

We need to create a concrete data manager that uses our protocol. Inside our folder Data/Local create a new swift file called DispatchManager.swift which implements DispatchManagerProtocol.

class DispatchManager: DispatchManagerProtocol {
    func save(message: String?) {

    }

    func retrieve() -> String? {
        return nil
    }

    func clear() {

    }
}

Move the code inside the DispatchViewController inside the methods of our new DispatchManager. Finally we need update our DispatchViewController in order to use the structured implementation.

Your DispatchViewController code should look like this:

import UIKit

class DispatchViewController: UIViewController {

    private let mainFlow: Flow = .login
    var dataManager: DispatchManagerProtocol! = DispatchManager()

    @IBOutlet weak var messageLabel: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()

        messageLabel.text = dataManager.retrieve()

        DispatchQueue.main.asyncAfter(deadline: .now() + 2) {
            self.setMainFlow(to: self.mainFlow)
        }
    }

}

Refactor structure

In the future the amount of local managers we are going to use migth increase, so before continue we need to crate some folders.

1. Click the Data/Local group inside Xcode to display the options menu, select "New group"
2. Rename the created folder to Protocols
3. Move the DispatchManagerProtocol file inside the Protocols group
4. Click the Data/Local group inside Xcode to display the options menu, select "New group"
5. Rename the created folder to Managers
6. Move the DispatchManager file inside the Managers folder

Challenge

Use UserDefaults to store:

• Session flag after user logs in
• Username entered by the user

Use the values stored to:

• Decide the main application flow (User should be redirected to pokemons list if has logged in)
• Display the user name as title for the pokemons screen. Use the template: Pokédex - <Username>

Bonus

Use the YellowPod - Local definition to combine the library DefaultsKit with our structured way to save values.