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?

if you want to share resources between the extension and the app, the best way is to create an _App Group_ and use the shared `UserDefault` (by `-suiteName:`) or the default `FileManager` (by `-forSecurityApplicationGroupIdentifier:`) only – you may not need the standard user-defaults or file-manager any longer (but if you need to be sure you want isolate data from the extension, you still can use those sandboxes). — holex, Aug 10 '17 at 08:15

score 83 · Accepted Answer · edited Mar 05 '20 at 07:00

You cannot use UserDefaults.standard to share data between a host app and its app extension. You instead have to create a shared container with 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 SuiteName?

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.

Apologies I assumed that as I was using ‘initSuiteName:’ that it would already give the impression I was using an App group. Which I am. Updated OQ to clarify this. Thanks — RyanTCB, Aug 10 '17 at 08:26
I’m current persisting same data to both standard & suiteName constructors. Should I just drop standard() and use suiteName. — RyanTCB, Aug 10 '17 at 08:32
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. — PGDev, Aug 10 '17 at 08:34
(shouldn't the references to "host app" in this answer actually refer to the "container app"?) — benc, Aug 14 '23 at 09:19

Tai Le · Answer 2 · 2021-01-03T02:59:06.187

77

Make sure App Groups is enabled for ALL OF YOUR TARGETS (your app and extensions targets) in the Capabilities tab

And then use the group's identifier above as suite name when create UserDefaults:

let userDefaults = UserDefaults(suiteName: "group.com.YourCompany.YourApp")

edited Jan 03 '21 at 02:59

answered Mar 10 '19 at 05:39

Tai Le

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This step is HIGHLY important. – P. Ent Nov 19 '20 at 15:32
Can we add any name to the group's identifier? – user4150758 Dec 06 '21 at 16:48
Thanks Tai Le. I was stuck on this. @user4150758 We have to set suiteName same as the App Groups name. otherwise it wan't work – Chirag Kalsariya Mar 08 '22 at 13:38

score 48 · Answer 3 · edited May 15 '20 at 12:37

48

A simple example where I create a shared bundle:

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

This is how you can read it later:

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

edited May 15 '20 at 12:37

Lucas van Dongen

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answered Mar 09 '18 at 13:57

oskarko

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You don't need to call `synchroniz` – BilalReffas Jun 21 '19 at 13:51
1

This does not actually answer the question which one to use. If you do what you have written wont work if data was saved from host application using UserDefaults.standard(). – Anuran Barman Aug 08 '19 at 11:14

score 14 · Answer 4 · answered Mar 04 '20 at 05:09

14

Also make sure you add App Groups to the correct Configuration (Debug, Release). If you add App Groups in Debug for your application target and try to use it in Release config for your extension, then it wont work.

If you add in Debug config (for app target), then use it in debug config (for extension target)

answered Mar 04 '20 at 05:09

Rahul Chhetri

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It was so simple and i waste an hour. Thanks for pointing that out – Swift Sharp Mar 10 '20 at 19:19
Meh I wish I had read this post before wasting 3 hours... I had my extension group only on profile... – mrj Mar 11 '21 at 17:12
1

@Rahul Chhetri Not sure I see where this would be added to a Debug only configuration. I don't see where App Groups can be assigned to a configuration. Please clarify – JeffB6688 Feb 08 '22 at 00:15
3

@JeffB6688 Okay I was confused by this initially. But as I was typing my original thoughts I discovered this. If you click on your project where the General, Signing & capabilities etc are. Select Signing & Capabilities, underneath that, there is "All, Debug, Release". This is what Rahul means by 'adding the app group to the debug and release' – Mark Feb 11 '22 at 23:44
Capabilities and Entitlements are sometimes managed by Xcode differently between `debug` and `release`, so this has probably happened to a lot of us. – benc Aug 14 '23 at 09:23

score 1 · Answer 5 · answered Mar 05 '20 at 07:03

PGDev: augmentation:

you can't avoid redundancy when dragging Settings (preferences) https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/UserDefaults/Preferences/Preferences.html to an extension: they are contained in the app private bundle and have to be replicated into suitenamed bundle to become available to an app extension

score 0 · Answer 6 · answered Jul 06 '23 at 22:19

Wasted a lot of time, and the problem was in adding of app groups only for release configuration, and of course while testing of debug configuration - I couldn't access to shared data between app extension and container app. So, be sure u adding app groups to both configurations - release and debug.

Sharing UserDefaults between extensions

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