Fix Switch crash when onChange fires after view recycle

[Mr-Perfectuz]

Summary:

Fixes #59203.

-[RCTSwitchComponentView onChange:] dereferences _eventEmitter without checking it. RCTViewComponentView -prepareForRecycle resets _eventEmitter, and on iOS 26+ the redesigned UISwitch can deliver its ValueChanged action from a deferred _UIAfterCACommitBlock (e.g. after a drag/long-press). If the view gets recycled in between, onChange: runs on a recycled view and crashes with EXC_BAD_ACCESS inside EventEmitter::dispatchEvent.

This adds an early return when _eventEmitter is null, matching the existing guards in RCTScrollViewComponentView, RCTImageComponentView, RCTModalHostViewComponentView and RCTVirtualViewComponentView. Dropping the event is correct since the recycled view no longer represents that React node.

Changelog:

[IOS] [FIXED] - Fix crash in Switch when onChange fires after the view has been recycled

Test Plan:

• The crash is intermittent and timing-dependent (reported from production), so it is not reproducible on demand.
• The change is limited to an early-return null guard before the emitter dereference; normal toggling in RNTester's Switch examples is unaffected since _eventEmitter is set for mounted views.

🤖 Generated with Claude Code

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[Mr-Perfectuz]

done CLA

[hcbylmz]

Thanks for the fix. The issue says the crash can't be reproduced on demand, so I wrote a unit test that hits this code path. It may help this PR get merged.

It fails on main and passes with your change. Tested on the iPhone 17 simulator (iOS 27), Xcode 27:

• Without the fix: the test crashes in -[RCTSwitchComponentView onChange:]. UBSan reports reference binding to null pointer of type 'const facebook::react::BaseViewEventEmitter'.
• With the fix: ** TEST SUCCEEDED **

The test calls the action directly. Unit tests run without UIApplication, so sendActionsForControlEvents: does not dispatch anything there. With that call the test passes even without the fix.

packages/rn-tester/RNTesterUnitTests/RCTSwitchComponentViewTests.mm

/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

#import <XCTest/XCTest.h>

#import <React/RCTSwitchComponentView.h>

@interface RCTSwitchComponentViewTests : XCTestCase
@end

@implementation RCTSwitchComponentViewTests

// UISwitch can deliver its value-changed action after the view was recycled
// (prepareForRecycle resets the event emitter). This must not crash.
- (void)testValueChangedAfterRecycleDoesNotCrash
{
  RCTSwitchComponentView *view = [[RCTSwitchComponentView alloc] initWithFrame:CGRectMake(0, 0, 51, 31)];
  [view prepareForRecycle];

  UISwitch *switchView = (UISwitch *)view.contentView;
  XCTAssertTrue([switchView isKindOfClass:[UISwitch class]]);

  [switchView setOn:YES animated:NO];

  // Unit tests run without UIApplication, so UIControl does not dispatch
  // actions. Invoke the registered action directly instead.
  NSArray<NSString *> *actions = [switchView actionsForTarget:view forControlEvent:UIControlEventValueChanged];
  XCTAssertEqual(actions.count, 1u);
  for (NSString *action in actions) {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
    [view performSelector:NSSelectorFromString(action) withObject:switchView];
#pragma clang diagnostic pop
  }
}

@end

The file also has to be added to the RNTesterUnitTests target in RNTesterPods.xcodeproj (4 lines in project.pbxproj). Run it with:

xcodebuild test -workspace RNTesterPods.xcworkspace -scheme RNTester \
  -destination 'platform=iOS Simulator,name=iPhone 17,OS=27.0' \
  -only-testing:RNTesterUnitTests/RCTSwitchComponentViewTests

Feel free to add it to this PR.

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