--- title: Two Files. One Difference. An 11× Bill You Never See. description: A deep dive into a subtle but costly SwiftUI performance pitfall: reading observable state in a parent view versus passing a stable handle to a child. Using... canonical: https://daily.dev/posts/two-files-one-difference-an-11-bill-you-never-see--ei9uyurk1 twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Two Files. One Difference. An 11× Bill You Never See. | daily.dev og:description: A deep dive into a subtle but costly SwiftUI performance pitfall: reading observable state in a parent view versus passing a stable handle to a child. Using... og:url: https://daily.dev/posts/two-files-one-difference-an-11-bill-you-never-see--ei9uyurk1 og:image: https://api.daily.dev/og/posts/ei9UYURk1.png og:image:alt: Two Files. One Difference. An 11× Bill You Never See. og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Two Files. One Difference. An 11× Bill You Never See. **[Medium](https://daily.dev/sources/medium_js)** · 12 min read · 0 upvotes · 0 comments ## Summary A deep dive into a subtle but costly SwiftUI performance pitfall: reading observable state in a parent view versus passing a stable handle to a child. Using Instruments profiler data, the author demonstrates that reading `counterValue` in the parent causes 11 parent rebuilds per 11 taps, while passing the handle down causes only 1. The post explains SwiftUI's dependency tracking rule ('whoever reads an observable property becomes a dependent'), connects it to real-world bugs like `@ObservedObject` vs `@StateObject` misuse and reload-on-revisit issues, and makes a case for a UIKit/SwiftUI hybrid architecture where UIKit owns navigation and lifecycle while SwiftUI handles rendering. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [SwiftUI data dependencies and their effect on view updates](https://daily.dev/posts/swiftui-data-dependencies-and-their-effect-on-view-updates-2kp42i6if) · Nil Coalescing · 1 upvotes · 0 comments - [Who Told The View To Update?](https://daily.dev/posts/who-told-the-view-to-update--xvxtydysb) · Medium · 0 upvotes · 0 comments - [@StateObject vs. @ObservedObject: The differences explained](https://daily.dev/posts/stateobject-vs-observedobject-the-differences-explained-m59jsolm0) · SwiftLee · 0 upvotes · 0 comments --- Tags: [#performance](https://daily.dev/tags/performance), [#ios](https://daily.dev/tags/ios), [#swift](https://daily.dev/tags/swift), [#swiftui](https://daily.dev/tags/swiftui) [View this post on daily.dev](https://daily.dev/posts/two-files-one-difference-an-11-bill-you-never-see--ei9uyurk1) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Two Files. 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