วิธีที่ SwiftUI คำนวณมุมมองใหม่

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.

When data changes, SwiftUI calls your view's body again to get a fresh description. This is normal and expected, not a bug.

SwiftUI compares the new description against the old one. This diffing step finds the small set of things that actually changed.

After diffing, only the parts that truly differ are redrawn. Everything else stays exactly as it was, which keeps updates fast.

For most views, SwiftUI compares them by value. If a struct's stored properties are unchanged, SwiftUI can skip work for that view.

SwiftUI also tracks a view's structural identity: its position in the view tree. Same slot means same view across updates.

You can give a view an explicit id. A changed id tells SwiftUI to treat it as a brand new view, resetting its state.

In a list, stable identity lets SwiftUI move rows instead of rebuilding them. Use a real id, not the array index.

A view re-evaluates only when a value it actually reads changes. These reads are its dependencies, and they define when body runs.

Running body is cheap; touching the GPU is not. A recompute often produces an identical result, so nothing is actually redrawn.

Knowing how SwiftUI diffs means you optimize the right thing: stable identity and minimal dependencies, not avoiding body calls entirely.

You saw that SwiftUI rebuilds body, diffs the result, and redraws only real changes. Identity and dependencies decide when that happens. 🧠