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[iOS][Fabric] TextInput drops a keystroke right after the first character typed into an empty field (_textOf:equals: compares attributes of a focused field)

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Evaluación

Dificultad
2/5
Tiempo estimado
1-3 horas
Aptitud para principiantes
78/100
Tipo de issue
Error
Claridad
Bien especificado
Estado de actividad
Activo
Stack tecnológico
ios, objective-c, react-native
Área
mobile

Línea de trabajo

Lee RCTTextInputComponentView.mm, especialmente _textOf:equals: y las comprobaciones existentes de dictado, texto marcado y entrada segura. Reproduce el caso de escritura rápida con el reproductor enlazado y compara su comportamiento antes y después de la comprobación de igualdad propuesta para el first responder. Se considera terminado cuando los mismos caracteres en un campo enfocado ya no activan la actualización que hace que se pierda una pulsación de tecla y el reproductor confirma que el problema está solucionado.

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

Needs: Attention Needs: Repro
Description

On iOS with the New Architecture (Fabric), typing quickly into an empty TextInput sometimes loses the second key. For example, typing «28» into an empty numeric field leaves «2». It happens only for the first character typed into an empty field, and only in a fast burst. Fields that already contain text are not affected.

We traced it as follows:

  1. The first character typed into an empty field reaches the native view with UIKit's typing attributes.
  2. The state round trip brings the same character back as an attributed string with React Native's full attribute set.
  3. -[RCTTextInputComponentView _textOf:equals:] compares the two strings including their attributes. It answers NO, although the characters are identical.
  4. React Native then calls setAttributedText: on the field while it is the first responder. That resets UIKit's keyboard / input pipeline, and the key in flight at that moment is dropped.

_textOf:equals: already has exceptions for dictation, Korean input, marked text and secure entry. One more exception fixes it in our app: while the backed text input view is the first responder, two strings with equal characters are treated as equal.

Suggested fix, in RCTTextInputComponentView.mm, _textOf:equals:: when _backedTextInputView is the first responder, compare only newText.string with oldText.string, next to the existing dictation / marked text / secure entry checks. Then a state round trip of the same characters never calls setAttributedText: on a focused field.

Workaround: we swizzle _textOf:equals: with that exception in a small native module, and will remove it once a release includes a fix.

Steps to reproduce
  1. Render an uncontrolled TextInput (defaultValue only, keyboardType="number-pad"). Leave it empty, and give it a style that sets fontSize, lineHeight and color.
  2. Focus it and type two digits quickly as one burst, for example «2» then «8» within about 100 ms.
  3. Repeat, emptying the field between runs.

Expected: «28». Actual: «2» in some of the bursts.

Our measurements (iOS 27 simulator, Release build):

  • without the exception, 5 of 13 two- and three-digit bursts lost a key;
  • with the exception, 0 of 12 did.
React Native Version

0.86.3

Affected Platforms

Runtime - iOS

Areas

Fabric - The New Renderer

Output of npx @react-native-community/cli info
System:
  OS: macOS 27
  CPU: Apple Silicon
Binaries:
  Node: 25.9.0
  Bun: 1.3.11
IDEs:
  Xcode: 27.0 (27A266a)
npmPackages:
  react: 19.2
  react-native: 0.86.3
  expo: 57
iOS:
  hermesEnabled: true
  newArchEnabled: true
Stacktrace or Logs
No crash or log: a key is silently lost. In the debugger, `-[RCTTextInputComponentView _textOf:equals:]` returns NO for an
equal one-character string (UIKit typing attributes vs React Native's attribute set), and `setAttributedText:` runs on the
first responder right before the lost key.
MANDATORY Reproducer

https://github.com/vdzerkalo/rn-58904-textinput-lost-key

Made from the reproducer template: react-native 0.87.1 (latest), New Architecture, no extra dependencies. Six empty, uncontrolled fields; each row compares the keys onKeyPress reported with the characters that landed in the field. iOS 27 simulator, Release: 9 of 18 bursts of «28» lost the second key; with the suggested change applied at runtime (-ApplySuggestedFix YES, off by default), 0 of 18.

Screenshots and Videos

One Release round each from the reproducer (iOS 27 simulator, a fresh launch, six bursts of «28»). Left: React Native 0.87.1 as is, 5 of 6 bursts lost the second key. Right: with the suggested change (-ApplySuggestedFix YES), 0 of 6.

As is With the suggested change
5 of 6 bursts of 28 ended as 2 0 of 6 bursts lost a key
Lenguaje dominante
C++
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Forks
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