This content originally appeared on DEV Community and was authored by Vinayak G Hejib
Understanding the truth behind SwiftUI’s most misunderstood property wrapper.
Why This Matters
Every SwiftUI developer uses @State. It’s the “magic” that makes your UI update when data changes.
But here’s the problem:
Most devs don’t actually know where that data is stored, how it survives view reloads, or why it sometimes behaves unexpectedly.
Misunderstanding @State leads to:
- ❌ Views not updating
- ❌ Data unexpectedly resetting
- ❌ Performance hits from unnecessary re-renders
Let’s lift the hood.
The Basics — What You Think Happens
struct CounterView: View {
@State private var count = 0
var body: some View {
VStack {
Text("\(count)")
Button("Increment") { count += 1 }
}
}
}
It feels like:
-
countis just a normal property on theCounterViewstruct. - When
countchanges, SwiftUI magically re-renders the view.
But… that’s not the whole story.
1. First Misconception — “@State is just a stored property”
Nope. It’s not stored inside your View struct.
SwiftUI views are value types — they get recreated all the time.
If @State lived directly in your struct, you’d lose its value every time your view re-rendered.
Instead, @State is a property wrapper that stores your data outside the view, in a special SwiftUI-managed heap storage.
Think of it like this:
- Your View struct is the blueprint.
- The
@Statestorage is the hidden container SwiftUI manages. - The two are connected by an ID SwiftUI assigns when the view hierarchy is built.
2. What Really Happens When You Declare @State
When SwiftUI first creates your view:
- It allocates a hidden storage object (a “State box”).
- This object lives for as long as the view identity stays the same in the hierarchy.
- Your view gets a reference to that box through the
wrappedValue.
Key point: View identity.
Change the identity (like swapping one .id for another in a List), and the storage disappears — @State resets to its initial value.
3. The Lifecycle in Real Time
Let’s track it:
- Initialization → SwiftUI allocates storage outside the struct.
- Mutation → You update the value, SwiftUI schedules a re-render.
-
Recreation → Your struct is replaced, but the
@Statebox is reattached. - Destruction → Identity changes → storage is destroyed.
💡 Real-world pitfall: if you’re building complex UIs with multiple conditional branches, you can accidentally reset state when toggling between branches.
The Reality — SwiftUI’s View Identity
SwiftUI views are structs. That means they are value types — new copies get created constantly.
So if @State really lived inside your view struct, you’d lose your data every time the view refreshed.
The trick?
@State stores your data outside the view — in SwiftUI’s internal storage system — and links it to your view via identity.
How Identity Works
When SwiftUI renders a view:
- It checks if the “new” view is the same identity as the previous one.
- If yes, it reuses the same
@Statestorage. - If no, it throws away the old storage and starts fresh.
Identity is determined by:
- View type
- Position in the view hierarchy
- Any explicit
.id(...)you set
Why It Matters for View Identity
State storage is tied to the identity of the view in the view hierarchy, not the variable name.
If SwiftUI thinks your view is different (e.g., changes id, order in the hierarchy, or parent view type), it will:
** Tear down the old storage **
Create new storage (resetting your @State)
Example:
if toggle {
MyView() // gets a new @State storage when toggle changes
} else {
MyView() // different identity => state resets
}
Fix: Give views a stable identity with .id(someStableValue) if you want state to persist.
That’s why reordering, wrapping in new containers, or changing .id can reset your @State.------
4. Where Does It Physically Live in Memory?
The @State wrapper conforms to DynamicProperty.
When compiled, SwiftUI injects a hidden _State struct that references a StateStorage object in the heap. That storage is owned and tracked by the SwiftUI runtime.
- Your View struct → on the stack
- Your
@Statedata → on the heap (safe from constant view re-creations)
5. Real-Time Issues You’ll Actually Hit
1️⃣ Data Reset on Navigation
NavigationLink("Open Detail", destination: DetailView())
If DetailView has @State and you navigate away & back — boom, your data resets.
Why? New view identity each time.
Fix: Use @StateObject or pass the data from a higher-level view.
2️⃣ State Not Updating
If your state depends on something that changes but your view identity stays constant, SwiftUI won’t refresh.
Sometimes you need .id(someValue) to force identity change.
3️⃣ Multiple Copies of State
Put a view with @State inside a List? Each row gets its own copy of state, tied to its own identity.
Reordering rows? State might shuffle or reset.
6. How to Think About @State
If UIKit was:
“I’ll hold onto this reference until you tell me otherwise,”
SwiftUI with @State is:
“I’ll keep this value alive for as long as your view’s identity stays in the tree — but break that link, and I’m tossing it.”
Key Takeaways
Rules of Thumb
- Use
@Statefor simple, view-local, short-lived data - If data must survive view re-creations, lift it up or use
@StateObject - Be careful with
.id(...)— it can reset your state - Remember: position in the view tree matters
@State is not a normal property — it’s SwiftUI’s way of outsourcing your data to an identity-bound container.
If your view’s identity changes, your @State starts fresh.
Once you truly understand that, you’ll stop fighting SwiftUI and start making it work for you.
This content originally appeared on DEV Community and was authored by Vinayak G Hejib
Vinayak G Hejib | Sciencx (2025-08-13T10:39:31+00:00) The Secret Life of @State in SwiftUI: Where Does My Data Actually Live?. Retrieved from https://www.scien.cx/2025/08/13/the-secret-life-of-state-in-swiftui-where-does-my-data-actually-live/
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