![]() ![]() This will happen in the init method of the FSDefaultsObserver class. It’s a key-value store backed by a property list (plist) file. It’s purpose will be to observe changes to the properties of our own user defaults class that inherits from FSUserDefaults that will call the appropriate set method of UserDefaults with the new value. User Defaults are the go-to solution for Swift applications to store preferences that persist across launches of your app. 1 Answer Sorted by: 3 If you are setting the default value in the AppDelegate you are setting that value back to 100 every time the app launches. ![]() In addition to a base FSUserDefaults class that we will inherit from (similarly to how it was done in Objective-C), an observer class is needed. However, KVO can be used to achieve the same effect. That means we can’t provide method implementations at run-time that effectively set and get values from UserDefaults when a property is accessed. In Swift, properties do not have setters and getters generated for them, and the dynamic keyword is used for Key-Value Observing. For example, you can allow users to specify their preferred units of measurement or media playback speed. The defaults system allows an app to customize its behavior to match a user’s preferences. (For a more detailed look at this, see the old post on NSUserDefaults.) Overview The UserDefaults class provides a programmatic interface for interacting with the defaults system. This allows us to dynamically provide the implementation methods for the setter and getter of dynamic properties using the -(BOOL)resolveInstanceMethod: method of NSObject. ![]() User Defaults are a great and simple way - built right into iOS to. In Objective-C, when you declare a property the compiler generates a setter and getter method along with a backing instance variable. Let's explore how to save and get data in an iOS app using UserDefaults. Having now primarily switched over to using Swift for iOS projects, I wanted to take a look at how to go about improving UserDefaults in the same way.Īt first it didn’t look like it was possible to achieve the same simplified API I ended up with for NSUserDefaults because Objective-C properties and Swift properties are fundamentally different. The data you associate with those keys can be one of several types - bool, number, string, URL, date, array, dictionary, or a bag-of-bytes (NSData). In your example, you would define your keys to be USERDEFAULTSLOGIN and USERDEFAULTSSUBSCRIPTION. This greatly simplified the string-based API of NSUserDefaults to make it much more convenient and safe to use. 1 UserDefaults API provides a way to set data for a key. I create a new custom object, Contact.A little while ago I wrote a post about improving NSUserDefaults in Objective-C using the Objective-C runtime. Decode Data back to Contact using JSONDecoder.Make an object conforms to the Codable protocol.We can convert an object to Data in three steps. Other Objectsįor non-property-list objects, we have to convert them to Data before saving them to UserDefaults.ĭata is also one of the Property-List objects. Sponsor and reach thousands of iOS developers. You can easily support by checking out this sponsor. We can also save an array of Dictionary if the key and value of the dictionary are supported types. array (forKey : "array" ) as ? ] Array of Dictionaries We can also save an array of Array if the inner one is an array of a supported type. stringArray (forKey : "names" ) Array of Arrays If you use this method, you don't need to cast the returning data to. func stringArray (forKey defaultName : String ) -> ? func array (forKey defaultName : String ) -> ?īut just for an array of strings, UserDefaults offers the dedicated method for retrieving an array of strings, stringArray(forKey:). That's because array(forKey:) returns an optional array of Any type ( ?). So far, we have to cast our Array to an appropriate type manually. array (forKey : "dates" ) as ? String Array array (forKey : "booleans" ) as ? Date Array The synchronize method is automatically invoked at periodic intervals, use this method only if you cannot wait for the automatic synchronization (for example, if your application is about to exit) or if you want to update the user defaults to what is on disk even though you have not made any changes. You can also read and write other number types, e.g., Float and Double. We can easily read and write an array for supported data types via the setter and getter methods. Property List object, e.g., string, number, date, and data. ![]() So, how you read and write an array to UserDefaults varies based on the element type. UserDefaults provide an interface to read and write many data types, including an array.īut you can only store an array of Property-List objects, e.g., string, number, boolean, date, array, dictionary, and data. ![]()
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