| name | ios-swiftui |
| description | Build declarative UI and manage data flow with SwiftUI in iOS. Use when building declarative SwiftUI views or managing data flow with property wrappers. |
| metadata | {"triggers":{"files":["**/*View.swift"],"keywords":["View","State","Binding","EnvironmentObject"]}} |
SwiftUI Expert
Priority: P0 (CRITICAL)
Role: iOS UI Expert. Prioritize smooth 60fps, clean data flow.
Implementation Guidelines
- Views: Small, composable structs. Extract subviews often to keep
body clean.
- State Selection (iOS 17+, default):
- @State for local simple data (Booleans, Strings, local view toggles).
- @State for VMs marked
@Observable (owning parent creates it once: @State private var vm = MyViewModel()).
- Plain
let/property for passed-in @Observable VMs — no wrapper needed, child views auto-track only the fields they read.
- Legacy (pre-iOS 17 or Combine
ObservableObject VMs):
- @StateObject for VMs (initialized only once in parent view).
- @ObservedObject for passed-in VMs (initialized by parent).
- Prefer migrating
ObservableObject VMs to @Observable when the deployment target allows it — see ios-state-management.
- Modifiers: Order matters sequentially. Apply layout modifiers before visual ones (e.g.,
.padding().background()).
- Preview: Always provide
PreviewProvider or #Preview for every view.
Verification Checklist (Mandatory)
Anti-Patterns
- No Logic in Body: Move calculations to ViewModel or computed vars. Keep
body for UI composition only.
- No ObservedObject Init: NOT init
@ObservedObject inside View settings — this causes leaks and performance issues.
- No New
ObservableObject VMs on iOS 17+: Use @Observable for new code; reserve ObservableObject/@Published for code that must support pre-17 or already depends on Combine operators.
- No Hardcoded Sizes: Use flexible frames and spacers for responsive UI.
Canonical response anchors
When this skill applies, preserve the following domain terminology or equivalent concrete examples in the answer when relevant:
- @State for local simple data
