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fix: check both pointer count and action before reusing MotionEvent #178528

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Merged
auto-submit merged 2 commits into from
Dec 5, 2025
Merged

fix: check both pointer count and action before reusing MotionEvent #178528

auto-submit merged 2 commits into from
Dec 5, 2025

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@letrungdo letrungdo commented Nov 14, 2025 •
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Fix issue #169486

Problem

After PR #178015 was merged, Android platform views experience gesture blocking after multi-touch operations (e.g., pinch-to-zoom). The issue occurs because:

  1. PR [Android] Encode the original pointer count in messages that represent Android touch events #178015 changed framework behavior to encode original pointer count in events
  2. Framework now sends events with different actions than the original MotionEvent
    • Example: Framework sends ACTION_MOVE (2) while original event is ACTION_POINTER_UP (6)
  3. The existing engine code only checked pointer count, not action
  4. This caused the engine to use original event with wrong action → gesture blocked

Logs Showing the Issue

trackedEvent.pointerCount=2, touch.pointerCount=2, trackedEvent.action=6 (ACTION_POINTER_UP), touch.action=2 (ACTION_MOVE) → Pointer counts MATCH, using original event → WebView receives ACTION_POINTER_UP but expects ACTION_MOVE → Gesture blocked! ❌

@letrungdo letrungdo requested a review from a team as a code owner November 14, 2025 14:23
@github-actions github-actions bot added platform-android Android applications specifically engine flutter/engine related. See also e: labels. team-android Owned by Android platform team labels Nov 14, 2025
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Code Review

This pull request provides a solid fix for a gesture-blocking issue on Android platform views. The problem, which occurred when the framework sent a MotionEvent with a different action than the original cached event, is correctly resolved by adding a check for the event action in addition to the pointer count before reusing a cached event. The logic is sound, and the changes are clean and well-commented. Furthermore, a new unit test, toMotionEvent_handlesActionMismatch, has been added. This test is comprehensive and accurately simulates the bug scenario, ensuring the fix is effective and preventing future regressions. The overall quality of the change is excellent.

@letrungdo letrungdo force-pushed the engine/fix-android-platform-views branch from bd780d2 to 2ae4107 Compare November 15, 2025 12:02
@letrungdo letrungdo force-pushed the engine/fix-android-platform-views branch from 2ae4107 to ca107d7 Compare November 15, 2025 15:38
@reidbaker reidbaker requested a review from gmackall November 17, 2025 16:10
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Can I ask what behavior you expect to see? I no longer see the behavior from #178528 that your original PR intended to fix (the platform view becoming unresponsive) on master. I'm not sure I can see a behavior difference when testing your app on this branch vs master:

on your branch:
https://github.com/user-attachments/assets/47fe92b4-e71f-4830-8cb1-1e808512dd7e

on master:
https://github.com/user-attachments/assets/8f7fb804-7c78-4522-9763-4980c26523f9

Naively, they both look correct to me (they discard multi touch gestures, as one would expect from a SingleTouchContainer and otherwise don't become unresponsive).

I also am doubtful that #178015 introduced the action mismatch you are highlighting here. Anecdotally I had noticed that this bug existed before either your original PR or @jason-simmons's pr had landed.

Given that your original PR still used the action from the tracked event when making the reconstructed event, I would expect no effect from @jason-simmons's PR on the behavior you see with regard to action delivered.

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letrungdo commented Nov 18, 2025 •
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@gmackall I added gestureRecognizers in the following commit
You can test again on the latest commit in this repo. It can be reproduced easily

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letrungdo commented Nov 28, 2025

@gmackall cc @reidbaker If you need any other information I will provide it right away.
This bug is very important to report to our customers. Thank you for your cooperation.

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gmackall commented Dec 1, 2025

We will need to resolve #179275 before landing this

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Ok it turns out this actually resolves #179275!

I also wanted to double check if we could, for the case where only the actions mismatch, call MotionEvent.setAction() and maintain verifiability. But it turns out that method renders the event not verified, so it seems pointer mismatch and action mismatch are the two cases where we can't fix the event and thus need to construct a new event. So this LGTM.

@gmackall gmackall added the autosubmit Merge PR when tree becomes green via auto submit App label Dec 4, 2025
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auto-submit bot commented Dec 4, 2025

autosubmit label was removed for flutter/flutter/178528, because The base commit of the PR is older than 7 days and can not be merged. Please merge the latest changes from the main into this branch and resubmit the PR.

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autosubmit label was removed for flutter/flutter/178528, because This PR has not met approval requirements for merging. The PR author is not a member of flutter-hackers and needs 1 more review(s) in order to merge this PR.

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@gmackall gmackall requested a review from a team December 4, 2025 23:39
@gmackall gmackall added the autosubmit Merge PR when tree becomes green via auto submit App label Dec 5, 2025
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Merged via the queue into flutter:master with commit 0179749 Dec 5, 2025
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engine-flutter-autoroll added a commit to engine-flutter-autoroll/packages that referenced this pull request Dec 5, 2025
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0179749 fix: check both pointer count and action before reusing Motio…
634432a 
…nEvent (flutter/flutter#178528)
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0179749 fix: check both pointer count and action before reusing Motio…
6dcf5eb 
…nEvent (flutter/flutter#178528)
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Roll Flutter from 69d8710 to 5b87203 (42 revisions) (#10574)
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reidbaker pushed a commit to AbdeMohlbi/flutter that referenced this pull request Dec 10, 2025
@letrungdo @reidbaker
fix: check both pointer count and action before reusing MotionEvent (f…
b961b2e 
…lutter#178528)

Fix issue flutter#169486

## Problem

After [PR flutter#178015](flutter#178015) was
merged, Android platform views experience gesture blocking after
multi-touch operations (e.g., pinch-to-zoom). The issue occurs because:

1. PR flutter#178015 changed framework behavior to encode original pointer
count in events
2. Framework now sends events with **different actions** than the
original MotionEvent
- Example: Framework sends `ACTION_MOVE (2)` while original event is
`ACTION_POINTER_UP (6)`
3. The existing engine code only checked **pointer count**, not action
4. This caused the engine to use original event with wrong action →
gesture blocked

### Logs Showing the Issue

trackedEvent.pointerCount=2, touch.pointerCount=2, trackedEvent.action=6
(ACTION_POINTER_UP), touch.action=2 (ACTION_MOVE) → Pointer counts
MATCH, using original event → WebView receives ACTION_POINTER_UP but
expects ACTION_MOVE → Gesture blocked! ❌
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