From 243aecc095c20f8295fdefa8fc3e3ac8a7691043 Mon Sep 17 00:00:00 2001
From: kirillzyusko <zyusko.kirik@gmail.com>
Date: Mon, 3 Feb 2025 07:27:58 -0800
Subject: [PATCH] fix: avoid `ConcurrentModificationException` (#49109)

Summary:
Fixes a `ConcurrentModificationException` when iterating over `TextWatcher` `mListeners` array.

If you open Android open source code (`TextView` class), then we can see that Android iterates with `for/n` loop (not `for/:`):

```java
    void sendAfterTextChanged(Editable text) {
        if (mListeners != null) {
            final ArrayList<TextWatcher> list = mListeners;
            final int count = list.size();
            for (int i = 0; i < count; i++) {
                list.get(i).afterTextChanged(text);
            }
        }

        notifyListeningManagersAfterTextChanged();

        hideErrorIfUnchanged();
    }
```

<hr>

We can catch the `ConcurrentModificationException` with old code, when for example we have 3 listeners:

- 0 is `EmojiTextWatcher` (seems like it's added by OS);
- 1 is `OnlyChangeIfRequiredMaskedTextChangedListener` (added by `react-native-text-input-mask`);
- 2 is a listener that attached by `react-native-keyboard-controller`.

On every afterTextChanged [input-mask-android](https://github.com/RedMadRobot/input-mask-android/tree/df452edc0c52a37e5082adcfc3d05d77b5aa34e8) [removes](https://github.com/RedMadRobot/input-mask-android/blob/df452edc0c52a37e5082adcfc3d05d77b5aa34e8/inputmask/src/main/kotlin/com/redmadrobot/inputmask/MaskedTextChangedListener.kt#L212) the listener and [adds](https://github.com/RedMadRobot/input-mask-android/blob/df452edc0c52a37e5082adcfc3d05d77b5aa34e8/inputmask/src/main/kotlin/com/redmadrobot/inputmask/MaskedTextChangedListener.kt#L231) it back.

The oversimplified version of the code can be next:

```java
public class MyClass {
    public static void main(String args[]) {
        ArrayList<Integer> mListeners = new ArrayList<>();
        mListeners.add(0);
        mListeners.add(1);
        mListeners.add(2);

        Iterator<Integer> iterator = mListeners.iterator();

        while (iterator.hasNext()) {
            Integer listener = iterator.next();

            // Check if the listener is equal to 1
            // 1 is OnlyChangeIfRequiredMaskedTextChangedListener and we simulate the behavior of this class
            if (listener == 1) {
                int i = mListeners.indexOf(listener);

                if (i >= 0) {
                    mListeners.remove(i);
                }

                // Add the removed element at the end
                mListeners.add(listener);
            }
        }

        // Print the modified list
        System.out.println(mListeners);
    }
}
```

Key points are:
- if we have only [0, 1] listener, then it works well and `ConcurrentModificationException` will not be thrown, because we modify last element;
- if we have `[0, 1, 2]` then exception will be thrown.

So in this PR I decided to re-work code to match what Android has. With `for/n` approach `ConcurrentModificationException` will not be thrown, because we don't check array immutability in this case.

More information also can be found here: https://github.com/kirillzyusko/react-native-keyboard-controller/issues/324

## Changelog:

[ANDROID] [CHANGED] - avoid `ConcurrentModificationException` when iterating over `mListeners` `TextWatcher` array

Pull Request resolved: https://github.com/facebook/react-native/pull/49109

Reviewed By: cortinico

Differential Revision: D69050984

Pulled By: javache

fbshipit-source-id: 9c6a7a428467fa5e546d70549dfcc91d6b2e58d2
---
 .../com/facebook/react/views/textinput/ReactEditText.java   | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/textinput/ReactEditText.java b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/textinput/ReactEditText.java
index 2282e43bd21..42f238363e8 100644
--- a/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/textinput/ReactEditText.java
+++ b/packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/textinput/ReactEditText.java
@@ -80,8 +80,8 @@ import com.facebook.react.views.text.internal.span.ReactStrikethroughSpan;
 import com.facebook.react.views.text.internal.span.ReactTextPaintHolderSpan;
 import com.facebook.react.views.text.internal.span.ReactUnderlineSpan;
 import com.facebook.react.views.text.internal.span.TextInlineImageSpan;
-import java.util.ArrayList;
 import java.util.Objects;
+import java.util.concurrent.CopyOnWriteArrayList;
 
 /**
  * A wrapper around the EditText that lets us better control what happens when an EditText gets
@@ -111,7 +111,7 @@ public class ReactEditText extends AppCompatEditText {
   /** A count of events sent to JS or C++. */
   protected int mNativeEventCount;
 
-  private @Nullable ArrayList<TextWatcher> mListeners;
+  private @Nullable CopyOnWriteArrayList<TextWatcher> mListeners;
   private @Nullable TextWatcherDelegator mTextWatcherDelegator;
   private int mStagedInputType;
   protected boolean mContainsImages;
@@ -390,7 +390,7 @@ public class ReactEditText extends AppCompatEditText {
   @Override
   public void addTextChangedListener(TextWatcher watcher) {
     if (mListeners == null) {
-      mListeners = new ArrayList<>();
+      mListeners = new CopyOnWriteArrayList<>();
       super.addTextChangedListener(getTextWatcherDelegator());
     }