How SwiftUI Recomputes Views
Understand identity, value, and diffing.
How SwiftUI Recomputes Views is a free SwiftUI Academy lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the SwiftUI Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Views Are Cheap Descriptions
A SwiftUI view is not a heavy object. It is a lightweight description of what the screen should look like right now. SwiftUI builds and discards them constantly.
body Runs Again and Again
When data changes, SwiftUI calls your view's body again to get a fresh description. This is normal and expected, not a bug.
var body: some View {
Text("Count: \(count)")
}Diffing the Two Trees
SwiftUI compares the new description against the old one. This diffing step finds the small set of things that actually changed.
Only Changes Reach the Screen
After diffing, only the parts that truly differ are redrawn. Everything else stays exactly as it was, which keeps updates fast.
Value Identity
For most views, SwiftUI compares them by value. If a struct's stored properties are unchanged, SwiftUI can skip work for that view.
Structural Identity
SwiftUI also tracks a view's structural identity: its position in the view tree. Same slot means same view across updates.
Explicit Identity with id
You can give a view an explicit id. A changed id tells SwiftUI to treat it as a brand new view, resetting its state.
ProfileView()
.id(selectedUser.id)Identity in ForEach
In a list, stable identity lets SwiftUI move rows instead of rebuilding them. Use a real id, not the array index.
ForEach(items) { item in
RowView(item: item)
}Dependencies Drive Updates
A view re-evaluates only when a value it actually reads changes. These reads are its dependencies, and they define when body runs.
Recompute Is Not Redraw
Running body is cheap; touching the GPU is not. A recompute often produces an identical result, so nothing is actually redrawn.
Why This Mental Model Matters
Knowing how SwiftUI diffs means you optimize the right thing: stable identity and minimal dependencies, not avoiding body calls entirely.
Quick Check
What does SwiftUI do after rebuilding a view's body?
Recap: How Views Recompute
You saw that SwiftUI rebuilds body, diffs the result, and redraws only real changes. Identity and dependencies decide when that happens. 🧠
Frequently asked questions
Is the “How SwiftUI Recomputes Views” lesson free?
Yes — the full text of “How SwiftUI Recomputes Views” is free to read here on the web, and the SwiftUI Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the SwiftUI Academy course, upgrade to CoddyKit PRO.
What will I learn in “How SwiftUI Recomputes Views”?
Understand identity, value, and diffing. You practise SwiftUI Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start SwiftUI Academy?
No prior experience is required. SwiftUI Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “How SwiftUI Recomputes Views” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this SwiftUI Academy lesson?
Yes. Every SwiftUI Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- How SwiftUI Recomputes Views
- Avoiding Unnecessary Redraws
- Lazy Loading Heavy Content
- Profiling with Instruments