@Stateと@Binding

Both @State and @Binding manage mutable data, but they play different roles. Picking the right one keeps ownership clear. 🎯

Use @State when this view is the source of truth. It creates and stores the value for itself.

Use @Binding when the value lives somewhere else and this view only needs to read and write it.

@State initializes a value. @Binding never does; it always receives one from a parent that owns it.

@State is view-local, so mark it private. No one outside should reach in and set it directly.

A @Binding is not private; the parent must be able to pass a value in when it creates the child.

An owners @State turns into a child @Binding through the dollar sign. That is the bridge between the two.

The view highest up that truly owns the data uses @State. Everything below it borrows with @Binding.

Ask: do I create this value? If yes, @State. If a parent hands it to me, @Binding. That choice rarely fails you.

Use @State where you meant @Binding and the child edits a copy. The parent never sees the change, and the UI quietly desyncs.

One piece of data is @State in its owner and @Binding in every borrower. Same value, different responsibilities. 🔄

Use @State to own a value and @Binding to borrow one. Match the wrapper to who creates the data and your views stay in sync. 🧠