Sharing UserDefaults between extensions

Question

Creating a Today widget and I am using UserDefaults(suiteName:) to persist some data. In the main application I am using UserDefaults.standard(). This can't be read (or can it?) by the extension which is why I use the suiteName: constructor.

Data that user persist to UserDefaults.standard() in the main app needs to be available in the extension.

At this time I am persisting to both so that the values can be shared

 UserDefaults.standard().set:...forKey:...
 UserDefaults(suiteName:...)().set:...forKey:...
 ...

Question is should I drop UserDefaults.standard() all together and just use UserDefaults(suiteName:) in my application, or is this bad practice and if so why?

Edit: I am using an App group container. For clarification I am asking should I just replace standard() with suiteName: throughout my project?

Answer 1

You cannot use shared UserDefaults to share data between and App Extension and its Host App. You have to use App Group, i.e. a shared container UserDefaults(suiteName:) to share data.

Even though an app extension bundle is nested within its containing app’s bundle, the running app extension and containing app have no direct access to each other’s containers.

To enable data sharing, use Xcode or the Developer portal to enable app groups for the containing app and its contained app extensions. Next, register the app group in the portal and specify the app group to use in the containing app.

After you enable app groups, an app extension and its containing app can both use the NSUserDefaults API to share access to user preferences. To enable this sharing, use the initWithSuiteName: method to instantiate a new NSUserDefaults object, passing in the identifier of the shared group.

For more, refer to: https://developer.apple.com/library/content/documentation/General/Conceptual/ExtensibilityPG/ExtensionScenarios.html#//apple_ref/doc/uid/TP40014214-CH21-SW1

How to use App Groups: https://github.com/pgpt10/Today-Widget

Standard or SuitName?

Use standard one for data that is only for Host App. Use suiteName for data that you want to share between Extension and Host App. Just don't persist the same data in both of them. Avoid data redundancy. Use both of them according to the context.

Answer 2

A simple example:

if let userDefaults = UserDefaults(suiteName: "group.your.bandle.here") {
    userDefaults.set("test 1" as AnyObject, forKey: "key1")
    userDefaults.set("test 2" as AnyObject, forKey: "key2")
    userDefaults.synchronize()
}

and you can read it later:

if let userDefaults = UserDefaults(suiteName: "group.your.bandle.here") {
    let value1 = userDefaults.string(forKey: "key1")
    let value2 = userDefaults.string(forKey: "key2")
    ...
}