Swizzling SwiftUI View Body

Noah Martin from Sentry cracked a problem that seemed impossible: swizzling pure Swift code to automatically track SwiftUI view performance. The technique is wild.

UIKit apps get automatic performance tracing through Objective-C swizzling, but SwiftUI's pure Swift types don't support this. Martin details how Sentry's ViewPerformance package achieves similar functionality by parsing protocol conformance descriptors and using software breakpoints to hook into every SwiftUI view body.

Key Takeaways

• Protocol conformance descriptors reveal all types conforming to SwiftUI.View at runtime
• Software breakpoints intercept function entry and exit without traditional swizzling
• Works in debug builds only due to executable modification restrictions
• Hardware breakpoints enable TestFlight use but require development mode enabled
• Open source ViewPerformance package available for immediate debug build integration

The article reveals why this technique shares DNA with iOS app launch optimization and what limitation prevents tracking generic SwiftUI views.