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.
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.
defaults.synchronize()
//Access UserDefaults
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
// Set a String value for some key.
[defaults setObject:@"Hello World" forKey:@"myString"];
// Set an Integer value for some key.
[defaults setInteger:123 forKey:@"myInt"];
// Set a Double value for some key.
[defaults setDouble:123.00 forKey:@"myDouble"];
// Set a Bool value for some key.
[defaults setBool:YES forKey:@"myBool"];
// Set a Data value for some key.
[defaults setObject:data forKey:@"currentUserData"];
// Force UserDefaults to save.
[defaults synchronize];
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.
To load a key from UserDefaults, do something like this:
// Access UserDefaults
let defaults = UserDefaults.standard//Access UserDefaults
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];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 = defaults.data(forKey: "myData")// Get a string value and provide a default string in the case the string is nil.
NSString *stringValue = [defaults stringForKey:@"myString"];
// Get an Integer value.
NSInteger intValue = [defaults integerForKey:@"myInt"];
// Get a Double value.
double doubleValue = [defaults doubleForKey:@"myDouble"];
// Get a Bool value.
BOOL boolValue = [defaults boolForKey:@"myBool"];
// Get a Data value
NSData *dataValue = [defaults dataForKey:@"myData"];