There are several different persistence mechanisms in iOS. The simplest to use is a persistent key-value store called UserDefaults. You might use UserDefaults for similar purposes as cookies in web development. They can store things like application settings, the current user, or a flag for whether a user has already seen a helpful hints popover.

Step 1: Saving Data

There are many data types that can be stored in UserDefaults including: array, bool, data, dictionary, float, integer, object, stringArray, string, double and url. Checkout the UserDefaults API Reference for more info.

To save a key to UserDefaults, do something like this:

//Access UserDefaults
let defaults = UserDefaults.standard

// Set a String value for some key.
defaults.set("Hello World!", forKey: "myString")
// Set an Integer value for some key.
defaults.set(123, forKey: "myInt")
// Set a Double value for some key.
defaults.set(123.00, forKey: "myDouble")
// Set a Bool value for some key.
defaults.set(true, forKey: "myBool")
// Set a Data value for some key.
defaults.set(data, forKey: "currentUserData")

// Force UserDefaults to save.

Note the synchronize call. UserDefaults automatically and periodically synchronizes, but to manually flush the keys and values to disk, call synchronize to guarantee that your updates are saved.

Step 2: Loading Data

To load a key from UserDefaults, do something like this:

// Access UserDefaults
let defaults = UserDefaults.standard

Get values of different types from a given key

// Get a string value and provide a default string in the case the string is nil.
let stringValue = defaults.string(forKey: "myString") ?? "my default string"
// Get an Integer value.
let intValue = defaults.integer(forKey: "myInt")
// Get a Double value.
let doubleValue = defaults.double(forKey: "myDouble")
// Get a Bool value.
let boolValue = defaults.bool(forKey: "myBool")
// Get a Data value
let dataValue = "myData")
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