Adapting Apple's Scrumdinger SwiftUI Tutorial App to Use Realm
Apple published a great tutorial to teach developers how to create iOS apps using SwiftUI. I particularly like it because it doesn't make any assumptions about existing UIKit experience, making it ideal for developers new to iOS. That tutorial is built around an app named "Scrumdinger," which is designed to facilitate daily scrum meetings.
Apple's Scrumdinger implementation saves the app data to a local file whenever the user minimizes the app, and loads it again when they open the app. It seemed an interesting exercise to modify Scrumdinger to use Realm rather than a flat file to persist the data. This article steps through what changes were required to rebase Scrumdinger onto Realm.
An immediate benefit of the move is that changes are now persisted immediately, so nothing is lost if the device or app crashes. It's beyond the scope of this article, but now that the app data is stored in Realm, it would be straightforward to add enhancements such as:
This article was updated in July 2021 to replace
objc and dynamic with the @Persisted annotation that was introduced in Realm-Cocoa 10.10.0.- Mac (sorry Windows and Linux users).
- Xcode 12.4+.
I strongly recommend that you at least scan Apple's tutorial. I don't explain any of the existing app structure or code in this article.
- The main branch is the app as it appears in Apple's tutorial. This is the starting point for this article.
- The realm branch contains a modified version of the Scrumdinger app that persists the application data in Realm. This is the finishing point for this article.
- You can view the diff between the main and realm branches to see the changes needed to make the app run on Realm.
From Xcode, select a simulator:
Build and run the app with
⌘r:
Create a new daily scrum. Force close and restart the app with
⌘r. Note that your new scrum has been lost 😢. Don't worry, that's automatically fixed once we've migrated to Realm.To use Realm, we need to add the Realm-Cocoa SDK to the Scrumdinger Xcode project using the Swift Package Manager. Select the "Scrumdinger" project and the "Swift Packages" tab, and then click the "+" button:
Paste in
https://github.com/realm/realm-cocoa as the package repository URL:
Add the
RealmSwift package to the Scrumdinger target:
We can then start using the Realm SDK with
import RealmSwift.To store an object in Realm, its class must inherit from Realm's
Object class. If the class contains sub-classes, those classes must conform to Realm's EmbeddedObject protocol.As with the original app's flat file, Realm can't natively persist the SwiftUI
Color class, and so colors need to be stored as components. To that end, we need a Components class. It conforms to EmbeddedObject so that it can be embedded in a higher-level Realm Object class. Fields are flagged with the @Persisted annotation to indicate that they should be persisted in Realm:DailyScrum is converted from a struct to an Object class so that it can be persisted in Realm. By conforming to ObjectKeyIdentifiable, lists of DailyScrum objects can be used within SwiftUI ForEach views, with Realm managing the id identifier for each instance.We use the Realm
List class to store arrays.The
History struct is replaced with a Realm Object class:The
ScrumData ObservableObject class was used to manage the copying of scrum data between the in-memory copy and a local iOS file (including serialization and deserialization). This is now handled automatically by Realm, and so this class can be deleted.Nothing feels better than deleting boiler-plate code!
Once the data is being stored in Realm, there's no need for lifecycle code to load data when the app starts or save it when it's minimized, and so
ScrumdingerApp becomes a simple wrapper for the top-level view (ScrumsView):The move from a file to Realm simplifies the top-level view.
The
DailyScrum objects are automatically loaded from the default Realm using the @ObservedResults annotation.New scrums can be added to Realm by appending them to the
scrums result set with $scrums.append(newScrum). Note that there's no need to open a Realm transaction explicitly. That's now handled under the covers by the Realm SDK.The main change to
DetailView is that any edits to a scrum are persisted immediately. At the time of writing (Realm-Cocoa 10.7.2), the view must open a transaction to store the change:As with
DetailView, MeetingView is enhanced so that meeting notes are added as soon as they've been created (rather than being stored in volatile RAM until the app is minimized):There are no changes needed to the view that's responsible for displaying a summary for a scrum. The changes we made to the
DailyScrum model in order to store it in Realm don't impact how it's used within the app.
Similarly, there are no significant changes needed to
EditView, HistoryView, MeetingTimerView, MeetingHeaderView, or MeetingFooterView.I hope that this post has shown that moving an iOS app to Realm is a straightforward process. The Realm SDK abstracts away the complexity of serialization and persisting data to disk. This is especially true when developing with SwiftUI.
Now that Scrumdinger uses Realm, very little extra work is needed to add new features based on filtering, synchronizing, and sharing data. Let me know in the community forum if you try adding any of that functionality.
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