@State สำหรับออบเจ็กต์ที่เป็นเจ้าของ

An observable model needs an owner: a view that creates it and keeps it alive for as long as the screen exists.

Use @State to let a view own an observable model. The view creates it once and holds onto it across redraws.

Without @State, a fresh model would be made on every redraw, wiping your data. @State persists the same instance.

Read tracked properties straight from the model in your body, and the view refreshes when they change.

Trigger behaviour by calling the model methods from your controls, keeping the view free of the actual logic.

Keep owned state private so other types cannot reach in and mutate the model behind the view back.

To read an observable model you use it directly. The dollar sign $ is only for making a binding, which we cover later.

Here a view owns the model, reads its value, and updates it on tap, all in one tidy place.

Because @State is managed by SwiftUI, your model survives every body re-evaluation while the view is on screen.

A model should have a single owner. Child views receive access instead of each making their own copy.

The model lives as long as its owning view. When the view leaves the screen for good, the model is released.

You used @State to let a view own its observable model, so a single instance survives redraws while the view reads and updates it. ✨