How to Store a String In User Defaults In Swift

The UserDefaults class allows developers to interact with the defaults system, a simple key-value store. The defaults system is available on iOS, tvOS, macOS, iPadOS, and watchOS. The defaults database can only be used to store a predefined set of data types, strings, numbers, Date objects, and Data objects. It is also possible to store arrays or dictionaries of these types.

Writing or Setting a String To User Defaults

Storing a string in the user's defaults database is simple. You first obtain a reference to the shared defaults object through the standard class property of the UserDefaults class.

import Foundation

// Access Shared Defaults Object
let userDefaults = UserDefaults.standard

To store the string in the user's defaults database, which is nothing more than a property list or plist, we pass the string to the set(_:forKey:) method of the UserDefaults class. We also need to pass a key as the second argument to the set(_:forKey:) method because we are creating a key-value pair. Remember that the defaults system is nothing more than a key-value store.

import Foundation

// Access Shared Defaults Object
let userDefaults = UserDefaults.standard

// Write/Set Value
userDefaults.set("myString", forKey: "myKey")

Reading or Getting a String From User Defaults

To read the string from the defaults database, we invoke the string(forKey:) method on the shared defaults object.

import Foundation

// Access Shared Defaults Object
let userDefaults = UserDefaults.standard

// Read/Get Value
let myString = userDefaults.string(forKey: "myKey")

The string(forKey:) method returns a value of type String?, an optional, because it is possible that the key-value pair doesn't exist in the defaults database.

You can also read the string from the user's defaults database by invoking the object(forKey:) method. The object(forKey:) method returns a value of type Any?, an optional. We cast it to a String object using the as? operator.

import Foundation

// Access Shared Defaults Object
let userDefaults = UserDefaults.standard

// Read/Get Value
let myString = userDefaults.object(forKey: "myKey") as? String

I'm sure you agree that the string(forKey:) method is the more elegant option and easier to read and understand. I strongly discourage you from using the as! operator to forced cast the result of object(forKey:) to a string. A runtime exception is thrown if the key that is passed to object(forKey:) doesn't exist or if the result can't be cast to a String object.

Use the exclamation mark sparingly in Swift. There's a good reason why it's an exclamation mark instead of a 🙂. You can read more about the exclamation mark on Cocoacasts.