Persistence using Codable

Objectives

Persistent data is information that is written to disk or to a web service that can be accessed after closing and reopening your iOS application.

Common tools for local persistence include plists, UserDefaults, and Core Data. This lesson covers saving our data to a file on disk.

• You will be able to make simple model objects which conform to the Codable protocol
• You will be able to persist data between app launches using Codable and plists
• You will be able to use CodingKeys to customize mapping between properties and JSON keys

Required Preclass Resources

Lesson Video

Video Challenges

• Add Properties

  Add some extra properties to the model object. Try adding properties of different types. See if you can run into a type that doesn't conform to Codable.

• Change from JSONEncoder to a PropertyListEncoder

  After using the PropertyListEncoder to encode your model object, print out the encoded data string and compare the differences to the JSONEncoder string.

Stretch Problem

Failable Initializers

Example Dictionary:

let workingDictionary = ["nameKey" : "Derek", "ageKey": 28, "favMovieKey" : "Zoolander"]
let brokenDictionary = ["nameKey" : "Steve", "ageKey": 2]

PART 1

1. Make a person class with name, age, and favoriteMovie properties
2. init the class with a dictionary of type string:anyobject.
3. Test this to make sure that it works

PART 2

1. Read about Failable Initializers
2. Use a guard statement to handle missing dictionary values
3. If a value is missing, don't init the person and instead return nil

♦ Black Diamond

Open your Journal project from yesterday. Create a function that will convert your Entry objects into dictionaries. Use this to encode all of the Entry objects stored in your sharedInstance as dictionaries, then print the result.

Hint

Solution

Guided Project

PlaylistCodable

PlaylistCodable is designed to introduce students to the Codable protocol.

Project

• Journal

  Students will build a simple Journal app to practice MVC separation, protocols, master-detail interfaces, table views, and persistence.

  Journal is an excellent app to practice basic Cocoa Touch princples and design patterns. Students are encouraged to repeat building Journal regularly until the principles and patterns are internalized and the student can build Journal without a guide.

  ReadMe

Mastery Review