How to save local data in a Swift app?

I'm currently working on a iOS app developed in Swift and I need to store some user-created content on the device but I can't seem to find a simple and quick way to store/receive the users content on the device.

Could someone explain how to store and access local storage?

The idea is to store the data when the user executes an action and receive it when the app starts.

The simplest solution for storing a few strings or common types is UserDefaults.

> The UserDefaults class provides convenience methods for accessing common types such as floats, doubles, integers, Boolean values, and URLs.

UserDefaults lets us store objects against a key of our choice, It's a good idea to store these keys somewhere accessible so we can reuse them.

Keys

struct DefaultsKeys {
    static let keyOne = "firstStringKey"
    static let keyTwo = "secondStringKey"
}

Setting

let defaults = UserDefaults.standard
defaults.set("Some String Value", forKey: DefaultsKeys.keyOne)
defaults.set("Another String Value", forKey: DefaultsKeys.keyTwo)

Getting

let defaults = UserDefaults.standard
if let stringOne = defaults.string(forKey: DefaultsKeys.keyOne) {
    print(stringOne) // Some String Value
}
if let stringTwo = defaults.string(forKey: DefaultsKeys.keyTwo) {
    print(stringTwo) // Another String Value
}

---

Swift 2.0

In Swift 2.0 UserDefaults was called NSUserDefaults and the setters and getters were named slightly differently:

Setting

let defaults = NSUserDefaults.standardUserDefaults()
defaults.setObject("Some String Value", forKey: DefaultsKeys.keyOne)
defaults.setObject("Another String Value", forKey: DefaultsKeys.keyTwo)

Getting

let defaults = NSUserDefaults.standardUserDefaults()
if let stringOne = defaults.stringForKey(DefaultsKeys.keyOne) {
    print(stringOne) // Some String Value
}
if let stringTwo = defaults.stringForKey(DefaultsKeys.keyTwo) {
    print(stringTwo) // Another String Value
}

---

For anything more serious than minor config you should consider using a more robust persistent store:

• CoreData
• Realm
• SQLite

They Say Use NSUserDefaults

When I was implementing long term (after app close) data storage for the first time, everything I read online pointed me towards NSUserDefaults. However, I wanted to store a dictionary and, although possible, it was proving to be a pain. I spent hours trying to get type-errors to go away.

NSUserDefaults is Also Limited in Function

Further reading revealed how the read/write of NSUserDefaults really forces the app to read/write everything or nothing, all at once, so it isn't efficient. Then I learned that retrieving an array isn't straight forward. I realized that if you're storing more than a few strings or booleans, NSUserDefaults really isn't ideal.

It's also not scalable. If you're learning how to code, learn the scalable way. Only use NSUserDefaults for storing simple strings or booleans related to preferences. Store arrays and other data using Core Data, it's not as hard as they say. Just start small.

Update: Also, if you add Apple Watch support, there's another potential consideration. Your app's NSUserDefaults is now automatically sent to the Watch Extension.

Using Core Data

So I ignored the warnings about Core Data being a more difficult solution and started reading. Within three hours I had it working. I had my table array being saved in Core Data and reloading the data upon opening the app back up! The tutorial code was easy enough to adapt and I was able to have it store both title and detail arrays with only a little extra experimenting.

So for anyone reading this post who's struggling with NSUserDefault type issues or whose need is more than storing strings, consider spending an hour or two playing with core data.

Here's the tutorial I read:

http://www.raywenderlich.com/85578/first-core-data-app-using-swift

If you didn't check "Core Data"

If you didn't check "Core Data"when you created your app, you can add it after and it only takes five minutes:

http://craig24.com/2014/12/how-to-add-core-data-to-an-existing-swift-project-in-xcode/

http://blog.zeityer.com/post/119012600864/adding-core-data-to-an-existing-swift-project

How to Delete from Core Data Lists

https://stackoverflow.com/questions/26047013/delete-data-from-coredata-swift

Okey so thanks to @bploat and the link to http://www.codingexplorer.com/nsuserdefaults-a-swift-introduction/

I've found that the answer is quite simple for some basic string storage.

let defaults = NSUserDefaults.standardUserDefaults()

// Store
defaults.setObject("theGreatestName", forKey: "username")

// Receive
if let name = defaults.stringForKey("username")
{
	print(name)
	// Will output "theGreatestName"
}

I've summarized it here http://ridewing.se/blog/save-local-data-in-swift/

Using NSCoding and NSKeyedArchiver is another great option for data that's too complex for NSUserDefaults, but for which CoreData would be overkill. It also gives you the opportunity to manage the file structure more explicitly, which is great if you want to use encryption.

For Swift 4.0, this got easier:

let defaults = UserDefaults.standard
//Set
defaults.set(passwordTextField.text, forKey: "Password")
//Get
let myPassword = defaults.string(forKey: "Password")

Swift 5+

None of the answers really cover in detail the default built in local storage capabilities. It can do far more than just strings.

You have the following options straight from the apple documentation for 'getting' data from the defaults.

func object(forKey: String) -> Any?
//Returns the object associated with the specified key.

func url(forKey: String) -> URL?
//Returns the URL associated with the specified key.

func array(forKey: String) -> [Any]?
//Returns the array associated with the specified key.

func dictionary(forKey: String) -> [String : Any]?
//Returns the dictionary object associated with the specified key.

func string(forKey: String) -> String?
//Returns the string associated with the specified key.

func stringArray(forKey: String) -> [String]?
//Returns the array of strings associated with the specified key.

func data(forKey: String) -> Data?
//Returns the data object associated with the specified key.

func bool(forKey: String) -> Bool
//Returns the Boolean value associated with the specified key.

func integer(forKey: String) -> Int
//Returns the integer value associated with the specified key.

func float(forKey: String) -> Float
//Returns the float value associated with the specified key.

func double(forKey: String) -> Double
//Returns the double value associated with the specified key.

func dictionaryRepresentation() -> [String : Any]
//Returns a dictionary that contains a union of all key-value pairs in the domains in the search list.

Here are the options for 'setting'

func set(Any?, forKey: String)
//Sets the value of the specified default key.

func set(Float, forKey: String)
//Sets the value of the specified default key to the specified float value.

func set(Double, forKey: String)
//Sets the value of the specified default key to the double value.

func set(Int, forKey: String)
//Sets the value of the specified default key to the specified integer value.

func set(Bool, forKey: String)
//Sets the value of the specified default key to the specified Boolean value.

func set(URL?, forKey: String)
//Sets the value of the specified default key to the specified URL.

If are storing things like preferences and not a large data set these are perfectly fine options.

Double Example:

Setting:

let defaults = UserDefaults.standard
var someDouble:Double = 0.5
defaults.set(someDouble, forKey: "someDouble")

Getting:

let defaults = UserDefaults.standard
var someDouble:Double = 0.0
someDouble = defaults.double(forKey: "someDouble")

What is interesting about one of the getters is dictionaryRepresentation, this handy getter will take all your data types regardless what they are and put them into a nice dictionary that you can access by it's string name and give the correct corresponding data type when you ask for it back since it's of type 'any'.

You can store your own classes and objects also using the func set(Any?, forKey: String) and func object(forKey: String) -> Any? setter and getter accordingly.

Hope this clarifies more the power of the UserDefaults class for storing local data.

On the note of how much you should store and how often, Hardy_Germany gave a good answer on that on this post, here is a quote from it

> As many already mentioned: I'm not aware of any SIZE limitation > (except physical memory) to store data in a .plist (e.g. > UserDefaults). So it's not a question of HOW MUCH. > > The real question should be HOW OFTEN you write new / changed > values... And this is related to the battery drain this writes will > cause. > > IOS has no chance to avoid a physical write to "disk" if a single > value changed, just to keep data integrity. Regarding UserDefaults > this cause the whole file rewritten to disk. > > This powers up the "disk" and keep it powered up for a longer time and > prevent IOS to go to low power state.

Something else to note as mentioned by user Mohammad Reza Farahani from this post is the asynchronous and synchronous nature of userDefaults.

> When you set a default value, it’s changed synchronously within your > process, and asynchronously to persistent storage and other processes.

For example if you save and quickly close the program you may notice it does not save the results, this is because it's persisting asynchronously. You might not notice this all the time so if you plan on saving before quitting the program you may want to account for this by giving it some time to finish.

Maybe someone has some nice solutions for this they can share in the comments?

Swift 3.0

Setter :Local Storage

let authtoken = "12345"
    // Userdefaults helps to store session data locally 
 let defaults = UserDefaults.standard                                           
defaults.set(authtoken, forKey: "authtoken")

 defaults.synchronize()

Getter:Local Storage

 if UserDefaults.standard.string(forKey: "authtoken") != nil {

//perform your task on success }

For Swift 3

UserDefaults.standard.setValue(token, forKey: "user_auth_token")
print("\(UserDefaults.standard.value(forKey: "user_auth_token")!)")

For someone who'd not prefer to handle UserDefaults for some reasons, there's another option - NSKeyedArchiver & NSKeyedUnarchiver. It helps save objects into a file using archiver, and load archived file to original objects.

// To archive object,
let mutableData: NSMutableData = NSMutableData()
let archiver: NSKeyedArchiver = NSKeyedArchiver(forWritingWith: mutableData)
archiver.encode(object, forKey: key)
archiver.finishEncoding()
return mutableData.write(toFile: path, atomically: true)

// To unarchive objects,
if let data = try? Data(contentsOf: URL(fileURLWithPath: path)) {
    let unarchiver = NSKeyedUnarchiver(forReadingWith: data)
    let object = unarchiver.decodeObject(forKey: key)
}

I've write an simple utility to save/load objects in local storage, used sample codes above. You might want to see this. https://github.com/DragonCherry/LocalStorage

NsUserDefaults saves only small variable sizes. If you want to save many objects you can use CoreData as a native solution, or I created a library that helps you save objects as easy as .save() function. It’s based on SQLite.

SundeedQLite

Check it out and tell me your comments

This gives a great explanation for how to do this in Swift 5: https://www.hackingwithswift.com/example-code/system/how-to-save-user-settings-using-userdefaults

Summary:

To set a value:

let defaults = UserDefaults.standard
defaults.set("value", forKey: "key")

To get a String value:

let key = defaults.object(forKey: "StringKey") as? [String] ?? [String]()

To get integer value:

let key = defaults.integer(forKey: "IntegerKey")