Andrei Calazans

React Native Weekly - W35 2021

☕️ 6 min read

Welcome to the 24th edition of React Native Weekly!

Week 35 - this is everything that happened between the 23rd and 29th of August 2021.

Improvements of the TextInput’s selection Prop

A parser and a primitive were added in C++. The selection prop is applied when component is mounted for iOS.

Fix Gradle pacakgeTask and asserts dir for Android libraries

Change by Leon Kiefer

This is an issue that started at 0.63. When building an android library the package task has a different name, which was not handled correctly in the react.gradle file. The fix uses the existing packageTask variable which is correctly set for applications and libraries.

This commit fixes issues like: and

Add codegen.js wrapper around

Héctor Ramos wrapped the Shell script with a Node.js program, I guess to make it more user friendly.

Usage: node ./codegen.js --srcs ./js --modules_library_name FBReactNativeSpec

Add support for the UIAccessibilityTraitsTabBar

Now you can set AccessibilityRole to 'tabbar’. Change.

Add window to jest setup

Timo Mämecke in this commit fixes an issue with tests where some libraries checked if window is undefined to determine if the code is running on a server:

const isServer = typeof window === 'undefined'

Remove usages of dynamic_casts that are used inside assertions

This is an interesting change because in it we learn that the React Native Core team wants to remove the RTTI flags. As it can also been seen in this other commit: “Remove RTTI from LayoutAnimations”.

This diff is part of a bigger effort to remove the RTTI flags.

To do so they need to remove occurrences of dynamic_cast and other functions that rely on runtime type informations.

In C++, RTTI’s have a bad rep for having bad performance, increasing bundle size to include the type informations, and for indicating a bad architecture.

Fixed dynamic behavior of Text adjustsFontSizeToFit={true} [Android]

A fix by Valentin Shergin He explains the adjustsFontSizeToFit was implemented in a way that expected the Yoga to call onMeasure on every text size change, which doesn’t happen.

Since he believe the issue is fixed in Fabric, and the proper fix would be too invasive, he included a workaround to mark the node as dirty to force remeasuring by Yoga.

onKeyPress event not fired with numeric keys [Android]

Diff by fabriziobertoglio1987

The TextInput onKeyPress event is not fired when pressing numeric keys on Android.

The method sendKeyEvent will dispatchKeyEvent only for:

  • KEYCODE_DEL (delete key)

Add 12 BLUETOOTH_ADVERTISE to Permissions [Android]

The latest Android 12 Beta build titled BLUETOOTH_ADVERTISE as a dangerous permissions requiring approval for them.

Diff by Connor Tumbleson

Added Fabric appwide feature flag

This diff, adds a new ReactFeatureFlag to enable or disable Fabric appwide.

Compare strings by value instead of reference

This change, while subtle, explains an interesting on going change to a new linker the core team is rolling out.

Summary by Vincent Lee LLD, our new iOS linker, is an ongoing effort to migrate our old outdated ld64 linker. As part of our effort to rollout LLD to all apps, we are making sure LLD reaches parity with ld64.

Due to Identical Code Folding (ICF), LLD and ld64 handles strings differently. LLD treats each string as a separate object in memory even if the values of the strings are the same. ld64 happens to aggregate these values across files. This behavior creates a subtle difference on our codebase when we start comparing by value or by reference.

char * fields from RawPropsKey.h are using == which compares by its address. Here, we cast the buffer to a string to make the comparison, while avoiding the cast if one happens to be null.

How the cast is done in C++:

+ return std::string(lhs) == std::string(rhs);

Remove DatePickerAndroid from React Native

Part of the lean core initiative. Removal

Show RedBox for C++ errors

Sota Ogo hooked up the cxx error to the redbox, previously they were only being logged and with Fabric more errors will come from C++.

Remove unsupported values for android_hyphenationFrequency [Android]

Diff by Genki Kondo

diff --git a/Libraries/Text/TextProps.js b/Libraries/Text/TextProps.js
index b2a39e58df7..3942a5998cd 100644
--- a/Libraries/Text/TextProps.js
+++ b/Libraries/Text/TextProps.js
@@ -66,13 +66,7 @@ export type TextProps = $ReadOnly<{|
    * Set hyphenation strategy on Android.
-  android_hyphenationFrequency?: ?(
-    | 'normal'
-    | 'none'
-    | 'full'
-    | 'high'
-    | 'balanced'
-  ),
+  android_hyphenationFrequency?: ?('normal' | 'none' | 'full'),
   children?: ?Node,

Fix alignItems: baseline for Text elements [Android]

This fixes and

Notes from Valentin Shergin

This is pretty much the same as 51b3529f6c2ca354800c0cf6ecb8eb3115eaa36e but implemented for Android. Now Text exposes the actual base-line offset value that allows Yoga to position it properly when alignItems: baseline is requested.


Screen Shot 2021-05-22 at 7 03 18 PM


Screen Shot 2021-05-22 at 7 01 51 PM

Optimize font handling on iOS (#31764)

A commit by Adlai Holler Certainly interesting to see a Google employee making a contribution to React Native ☺️. Adlai is someone who has contributed to Flutter as well.

Summary by Adlai:

Few issues I saw when profiling RNTester:

  • Repeatedly calling -lowercaseString during weightOfFont causes a TON of extra memory traffic, for no reason.
  • NSCache is thread-safe, so no need for a mutex.
  • Using stringWithFormat: for the cache key is slow. Use NSValue to store the data directly instead.
  • Calling -fontDescriptor in isItalicFont and isCondensedFont is overly expensive and unnecessary.
  • +fontNamesForFamilyName: is insanely expensive. Wrap it in a cache.

Unscientific test on RNTester iPhone 11 Pro, memory & time. Before:

Screen Shot 2021-06-23 at 7 40 06 AMScreen Shot 2021-06-23 at 7 41 30 AM


Screen Shot 2021-06-23 at 9 02 54 AMScreen Shot 2021-06-23 at 8 59 44 AM

Make JSI a dynamic library


Summary by Neil Dhar Ship libjsi as a standalone dynamic library. This prevents problems with exception handling caused by duplicate typeinfo across multiple shared libs, and reduces bundle size by removing duplicate copies of JSI.

Fabric updates

There were multiple PRs that continues to implement feature parity between the legacy modules and the new Fabric modules, examples were:

  • 53c6494615f Remount children in scrollView if layout changes
  • ca60be88825 Add android_hyphenationStrategy to ParagraphAttributes
  • 3b2d5419899 Set textBreakStrategy default to be HighQuality
  • ca60be88825 Add android_hyphenationStrategy to ParagraphAttributes
  • and more

React Native Many Platform Post

In this blogpost by the Core Team they highlighted their work towards bringing React Native to many platforms.

The best part of this is how React Native benefits from working happening on each front, an example was how “View Flattening” implemented only for Android at first was later shipped for iOS improving performance there as well.

Realtime Photo Color Palette Generator

Marc opened source a realtime photo color palette generator he built with React Native.

See the tweet. Marc is on 🔥

react-native-shared-element updates

Hein Rutjes tweeted how react-native-shared-element has received much needed updates and now supports React Navigation v6.

That Is It!

That’s it for this week. If you want to see more checkout the previous week’s posts here. Subscribe to get notified when new posts are out = )