How to save local data in a Swift app?

问题

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.

回答1:

The simplest solution if you are just storing two strings is NSUserDefaults, in Swift 3 this class has been renamed to just UserDefaults.

It's best to store your keys somewhere globally so that you can reuse them elsewhere in your code.

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

Swift 3.0, 4.0 & 5.0

// 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

// 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, flags or base strings you should use some sort of persistent store - A popular option at the moment is Realm but you can also use SQLite or Apples very own CoreData.

回答2:

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

Delete Data from Coredata Swift

回答3:

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/

回答4:

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.

回答5:

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")

回答6:

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 }

回答7:

For Swift 3

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

回答8:

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

回答9:

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

来源：https://stackoverflow.com/questions/28628225/how-to-save-local-data-in-a-swift-app