การประกาศพร็อพเพอร์ตี @State

You declare mutable view-local data by marking a property with @State. This property wrapper tells SwiftUI to store and watch the value for you. 🏷️

A @State property needs an initial value right where you declare it. SwiftUI uses it to create the storage the first time the view appears.

State belongs to one view, so declare it private. This signals that no outside code should reach in and set it directly, keeping ownership clear.

Read a @State property like any normal variable. Just use its name in body and SwiftUI tracks that this view depends on it.

You can mutate a @State property even though the view is a struct. Assign to it from an action and SwiftUI schedules a redraw automatically.

SwiftUI keeps the @State value alive across the many times the view body is recomputed. Your count won't reset just because the view redrew.

Declare state, read it in the body, and mutate it from a button. That is the full loop that powers most simple interactions.

@State works best with value types like Int, Bool, String, or small structs. For shared objects you'll later reach for other tools, but values are the norm here.

The view that declares @State is its owner. Other views can receive access, but only one view should hold the original state for a given value.

Reach for @State only when a value truly changes while the view is on screen. Constant labels and passed-in data don't need it.

Name state for what it represents, like isLoading or selectedTab. Clear names make the data flow obvious to anyone reading the view.

Declare changing view data with @State, give it a default, and keep it private. Read it freely in body and mutate it from actions to trigger redraws. ✅