Sharing Data Between iOS App and Widget Using App Groups

Slipi App Mock Up

When building Slipi, I wanted both the iOS app and its widget to display the same sleep data — in real time. But I quickly learned that normal UserDefaults doesn’t automatically share data between the app and its widget.

That’s when I discovered App Groups — Apple’s way of allowing different parts of the same app (like the main app and extensions) to share information securely. It was my first time setting it up, and here’s what I learned from the process.

⚙️ Setting Up App Groups

Insert screenshot of Xcode App Groups setup here

To make shared data possible, I had to configure App Groups correctly in the Apple Developer portal and Xcode.
Here are the steps I followed:

Create App ID for the Containing App
This represents the main iOS app (e.g., Slipi).
Create App ID for the Extension (Widget)
This represents the widget extension that displays sleep info.
Create an App Group
In the Developer portal, I created a new App Group with an identifier like group.com.example.slipi.
Assign the App Group to the Containing App’s App ID
This allows the main app to read and write data to the shared group container.
Assign the App Group to the Extension’s App ID
This connects the widget to the same container, enabling both sides to access shared data.

📚 Reference: Today Widget by @pgpt10 on GitHub

💻 Using Shared UserDefaults

After setting up App Groups, I needed to update my code to use a shared data container instead of the default one.

Previously, I used:

let defaults = UserDefaults.standard

But now, I had to reference the shared App Group:

let defaults = UserDefaults(suiteName: "group.com.example.slipi")

This new suiteName connects both the app and the widget to the same UserDefaults container, so any change in one will be reflected in the other.

💡 Tip: Make sure the group identifier matches exactly with the one registered in the Apple Developer portal — a typo here can break data sharing completely.

🧠 What I Learned

Normal UserDefaults doesn’t sync between apps and extensions — App Groups are required.
You must create and assign the App Group to both the main app and the widget’s App IDs.
Always use the exact group identifier when initializing UserDefaults(suiteName:).
Shared UserDefaults makes it easy to sync lightweight data like settings, scores, or small state info between app components.

After I got this working, seeing the sleep data instantly appear in the widget felt super satisfying — a small detail that made the overall experience more seamless.

✨ Closing Thoughts

This was a simple yet valuable lesson in app architecture and data sharing. Even though it’s just a few extra setup steps, understanding App Groups taught me how iOS apps handle isolation and communication securely.

It’s small discoveries like this that make iOS development exciting — every technical limitation opens a door to learning something new