fix: implement RCTAppearanceProxy#2729
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Saadnajmi merged 4 commits intomicrosoft:mainfrom Oct 14, 2025
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Co-authored-by: Tommy Nguyen <4123478+tido64@users.noreply.github.com>
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Summary:
React Native primarily runs on 2 threads: the UI thread (main thread for apple) and the JS thread (where the Javascript engine is running). This poses a challenge when JS synchronously wants a value that can only be accessed on the main thread (
getColorScheme()is the issue in this case).React Native upstream solves this via proxy objects (all initialized in
RCTInitializeUIKitProxies()called on RN instance startup) that set an initial value, and then guard reading / setting updated values of the main-thead-only values we want.Lets implement that for NSAppearance so we can fix a bunch of main thread violations we've been seeing on boot. I chose not to ifdef
RCTTraitCollectionProxybecause the names are quite different.. althought that would be the right file.Test Plan:
No main thread checker violations on RNTester boot.