swiftui-debugging

# SwiftUI Debugging ## Overview Systematic approaches for debugging SwiftUI issues in macOS apps. Covers view updates, state ownership, performance, layout, and macOS-specific quirks with NSHostingView and NSPanel. ## Logging in macOS Apps `print()` and `NSLog()` are invisible when launching macOS apps from CLI or Finder (menubar-only apps have no console). Always use file-based logging: ```swift func debugLog(_ message: String) { let entry = "\(Date()) \(message)\n" let url = URL(fileURLWithPath: "/tmp/debug.log") if let handle = try? FileHandle(forWritingTo: url) { handle.seekToEndOfFile() handle.write(entry.data(using: .utf8)!) handle.closeFile() } else { try? entry.write(to: url, atomically: true, encoding: .utf8) } } ``` Remove all debug logging before committing. Use `grep -r "debugLog" --include="*.swift"` to verify. ## View Not Updating ### Symptom View shows stale data after a confirmed state change. Common with `hostingView.rootView = NewView(...)` not propagating to children, or theme/color changes not reflecting. ### Root Cause: SwiftUI Diffing SwiftUI skips re-evaluating a child view's `body` if the child's struct inputs haven't changed — even if the child reads from a singleton or computed property that did change. ``` Parent: rootView = MyView(counts: same) → SwiftUI: "counts didn't change, skip child body" → Child: never re-reads StatusColors.working → Result: stale colors ``` ### Diagnosis...