Swift: how i can persist data when the app will be closed

Question

I made an .append to an array like this:

@IBOutlet var textField: UITextField? = nil
var array = ["item1", "item2", "item3"]

@IBAction func buttonPressed(_ sender: Any) {
    array.append((textField?.text?.lowercased())!)
}

This works good, but how could I save the appended strings even when the app will be closed?

Duncan C · Accepted Answer · 2017-03-28T19:42:11.643

1

Save the array to UserDefaults, and read it back on app launch.

var itemsArray = [String]()

...

itemsArray = UserDefaults.standard.object(forKey: "arrayKey") as? [String] ?? []

And to save it:

UserDefaults.standard.set(itemsArray, forKey: "arrayKey")

edited Mar 28 '17 at 19:42

answered Mar 28 '17 at 18:28

Duncan C

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I start learning swift from 3 weeks ago, how I save array in UserDefaults? – cisc0 Mar 28 '17 at 18:30
Thanks for your help – cisc0 Mar 28 '17 at 18:44
App data should not be saved to user defaults. Write the array to a file (plist). – rmaddy Mar 28 '17 at 18:45
UserDefaults has a specific method for loading arrays `UserDefaults.standard.array(forKey: "arrayKey") as? [String] ?? []` – Leo Dabus Mar 28 '17 at 18:51
and set is wrong. should be `UserDefaults.standard.set(itemsArray, forKey: "arrayKey")` – Leo Dabus Mar 28 '17 at 18:51
Data in UserDefaults should only contain user preference, like volume, language, currency etc. – J. Doe Mar 28 '17 at 18:54
https://developer.apple.com/library/content/documentation/FileManagement/Conceptual/FileSystemProgrammingGuide/FileSystemOverview/FileSystemOverview.html – Leo Dabus Mar 28 '17 at 18:55
but if I have multiple arrays? I have five buttons, when I press a button, the string goes in one of the five arrays. @LeoDabus – cisc0 Mar 28 '17 at 19:00
You can have it all inside a property list file as suggested by @rmaddy – Leo Dabus Mar 28 '17 at 19:21
you will need to use NSKeyedArchiver to convert your object to data and save it to disk – Leo Dabus Mar 28 '17 at 19:35
Note that your objects must conform to NSCoding http://stackoverflow.com/a/37983027/2303865 – Leo Dabus Mar 28 '17 at 19:36
rmaddy is right, saving app data to UserDefaults is bad form. Better to save it to a plist file in your documents directory. – Duncan C Mar 28 '17 at 19:43

Swift: how i can persist data when the app will be closed

1 Answers1