CS193p Notes - Lecture 13: Persistence

• UserDefaults
  • Simple. limited. small.
• Codable/JSON
  • Clean way to turn almost any data structure into an interoperable/storable format
• UIDocument
  • This is really the way to do things when you have a true document like EmojiArt has
  • UIKit compatibility code is required (no SwiftUI interface to it yet [THIS IS SwiftUI COURSE])
• Core Data
  • Powerful. Object-oriented. Elegant SwiftUI integration.
• Cloud Kit
  • Storing data into a database in the cloud
  • Has UserDefaults-like thing
  • Plays nicely with Core Data

Cloud Kit

• Record Type = like a class or struct
• Fields = like vars in a class or struct
• Record = an "instance" of a Record Type
• Reference = a "pointer" to another Record
• Database = a place where Records are stored
• Zone = a sub-area of a Database
• Container = collection of Databases
• Query = a Database search
• Subscription = a "standing Query" which sends push notifications when changes occur

iCloud needs to be turned on from Project Settings under Capabilities tab. Choose CloudKit from Services. Click CloudKit Dashboard.

let db = CKContainer.default.public/shared/privateCloudDatabase
let tweet = CKRecord("Tweet")
tweet["text"] = "140 characters of pure joy"
let tweeter = CKRecord("TwitterUser")
tweet["tweeter"] = CKReference(record: tweeter, action: .deleteSelf)
db.save(tweet) { (savedRecord: CKRecord?, error: NSError?) -> Void in
  if error == nil {
    // hooray!
  } else if error?.errorCode == CKErrorCode.NotAuthenticated.rawValue {
    // tell user he or she has to be logged in to iCloud for this to work
  } else {
    // report other errors (there are 29 different CKErrorCodes!)
  }
}

• File System
  • Unix file system
  • an app can read and write only it's own "sandbox"
  • Sandbox is useful because
    • No one else can damage app
    • other apps can't view your app's data
    • by deleting the sandbox, it's simple to get rid of all the data
  • Sandbox contains
    • Application directory - Your executable, .jpgs, etc.; not writable
    • Documents directory - Permanent storage created by and always visible to the user
    • Application Support directory - Permanent storage not seen directly by the user
    • Caches directory - Store temporary files here (this is not backed up)
    • Other directories (see documentation) ...

let predicate = NSPredicate(format: "text contains %@", searchString)
let query = CKQuery(recordType: "Tweet", predicate: predicate)
db.perform(query) { (records: [CKRecord]?, error: NSError?) in
  if error == nil {
    // records will be an array of matching CKRecords
  } else if error?.errorCode == CKErrorCode.NotAuthenticated.rawValue {
    // tell user he or she has to be logged in to iCloud for this to work!
  } else {
    // report other errors (there are 29 different CKErrorCodes!)
  }
}

@RealLankinen

• Notes 1
• Notes 2
• Notes 3
• Notes 4
• Notes 5
• Notes 6
• Notes 7
• Notes 8
• Notes 9
• Notes 10
• Notes 11
• Notes 12
• Notes 13
• Notes 14

Originally published here