iOS Crash in previewDocument() with React Native 0.84.1

[Akilramki]

iOS Crash in previewDocument() with React Native 0.84.1

Environment

• React: 19.2.3
• React Native: 0.84.1
• react-native-blob-util: 0.24.9
• Platform: iOS

---

Issue

Calling the following method:

RNFetchBlob.ios.previewDocument(filePath);

causes a Main Thread Checker crash/warning on iOS.

---

Error Logs

Main Thread Checker: UI API called on a background thread: -[UIApplication delegate]

Queue name: ReactNativeBlobUtil.queue

Backtrace:
-[ReactNativeBlobUtil presentOptionsMenu:scheme:resolve:reject:]

---

Additional Logs

Can't show source file for stack frame:
@objc AppDelegate.window.getter

The file path does not exist on the file system:
/<compiler-generated>

---

Full Logs

=================================================================
=================================================================
Main Thread Checker: UI API called on a background thread: -[UIApplication delegate]
PID: 57911, TID: 449216, Thread name: (none), Queue name: ReactNativeBlobUtil.queue, QoS: 0
Backtrace:
5   app                                 0x000000010384e548 -[ReactNativeBlobUtil presentOptionsMenu:scheme:resolve:reject:] + 448
6   CoreFoundation                      0x00000001804c80c0 __invoking___ + 144
7   CoreFoundation                      0x00000001804c5320 -[NSInvocation invoke] + 276
8   CoreFoundation                      0x00000001804c55a4 -[NSInvocation invokeWithTarget:] + 60
9   React                               0x000000010c68b49c ___ZN8facebook5react15ObjCTurboModule23performMethodInvocationERNS_3jsi7RuntimeEbPKcP12NSInvocationP14NSMutableArray_block_invoke + 196
10  React                               0x000000010c6a1e8c _ZZN8facebook5react15ObjCTurboModule23performMethodInvocationERNS_3jsi7RuntimeEbPKcP12NSInvocationP14NSMutableArrayENK3$_1clEv + 116
11  React                               0x000000010c6a1e0c _ZNSt3__18__invokeB8de190102IRZN8facebook5react15ObjCTurboModule23performMethodInvocationERNS1_3jsi7RuntimeEbPKcP12NSInvocationP14NSMutableArrayE3$_1JEEEDTclclsr3stdE7declvalIT_EEspclsr3stdE7declvalIT0_EEEEOSF_DpOSG_ + 24
12  React                               0x000000010c6a1dc4 _ZNSt3__128__invoke_void_return_wrapperIvLb1EE6__callB8de190102IJRZN8facebook5react15ObjCTurboModule23performMethodInvocationERNS3_3jsi7RuntimeEbPKcP12NSInvocationP14NSMutableArrayE3$_1EEEvDpOT_ + 24
13  React                               0x000000010c6a1da0 _ZNSt3__110__function12__alloc_funcIZN8facebook5react15ObjCTurboModule23performMethodInvocationERNS2_3jsi7RuntimeEbPKcP12NSInvocationP14NSMutableArrayE3$_1NS_9allocatorISE_EEFvvEEclB8de190102Ev + 28
14  React                               0x000000010c6a0b1c _ZNSt3__110__function6__funcIZN8facebook5react15ObjCTurboModule23performMethodInvocationERNS2_3jsi7RuntimeEbPKcP12NSInvocationP14NSMutableArrayE3$_1NS_9allocatorISE_EEFvvEEclEv + 28
15  React                               0x000000010c6b0108 _ZNKSt3__110__function12__value_funcIFvvEEclB8de190102Ev + 60
16  React                               0x000000010c6afff8 _ZNKSt3__18functionIFvvEEclEv + 24
17  React                               0x000000010c6b00c0 ___ZN12_GLOBAL__N_129ModuleNativeMethodCallInvoker11invokeAsyncERKNSt3__112basic_stringIcNS1_11char_traitsIcEENS1_9allocatorIcEEEEONS1_8functionIFvvEEE_block_invoke + 44
18  libdispatch.dylib                   0x00000001080e3ee8 _dispatch_call_block_and_release + 24
19  libdispatch.dylib                   0x00000001080fd374 _dispatch_client_callout + 12
20  libdispatch.dylib                   0x00000001080ebfa4 _dispatch_lane_serial_drain + 888
21  libdispatch.dylib                   0x00000001080ecc0c _dispatch_lane_invoke + 428
22  libdispatch.dylib                   0x00000001080f8bf8 _dispatch_root_queue_drain_deferred_wlh + 324
23  libdispatch.dylib                   0x00000001080f815c _dispatch_workloop_worker_thread + 752
24  libsystem_pthread.dylib             0x0000000107a1ec28 _pthread_wqthread + 288
25  libsystem_pthread.dylib             0x0000000107a1da28 start_wqthread + 8


Main Thread Checker: UI API called on a background thread: -[UIApplication delegate]
PID: 57911, TID: 449216, Thread name: (none), Queue name: ReactNativeBlobUtil.queue, QoS: 0
Backtrace:
5   app                                 0x000000010384e548 -[ReactNativeBlobUtil presentOptionsMenu:scheme:resolve:reject:] + 448
6   CoreFoundation                      0x00000001804c80c0 __invoking___ + 144
7   CoreFoundation                      0x00000001804c5320 -[NSInvocation invoke] + 276
8   CoreFoundation                      0x00000001804c55a4 -[NSInvocation invokeWithTarget:] + 60
9   React                               0x000000010c68b49c ___ZN8facebook5react15ObjCTurboModule23performMethodInvocationERNS_3jsi7RuntimeEbPKcP12NSInvocationP14NSMutableArray_block_invoke + 196
10  React                               0x000000010c6a1e8c _ZZN8facebook5react15ObjCTurboModule23performMethodInvocationERNS_3jsi7RuntimeEbPKcP12NSInvocationP14NSMutableArrayENK3$_1clEv + 116
11  React                               0x000000010c6a1e0c _ZNSt3__18__invokeB8de190102IRZN8facebook5react15ObjCTurboModule23performMethodInvocationERNS1_3jsi7RuntimeEbPKcP12NSInvocationP14NSMutableArrayE3$_1JEEEDTclclsr3stdE7declvalIT_EEspclsr3stdE7declvalIT0_EEEEOSF_DpOSG_ + 24
12  React                               0x000000010c6a1dc4 _ZNSt3__128__invoke_void_return_wrapperIvLb1EE6__callB8de190102IJRZN8facebook5react15ObjCTurboModule23performMethodInvocationERNS3_3jsi7RuntimeEbPKcP12NSInvocationP14NSMutableArrayE3$_1EEEvDpOT_ + 24
13  React                               0x000000010c6a1da0 _ZNSt3__110__function12__alloc_funcIZN8facebook5react15ObjCTurboModule23performMethodInvocationERNS2_3jsi7RuntimeEbPKcP12NSInvocationP14NSMutableArrayE3$_1NS_9allocatorISE_EEFvvEEclB8de190102Ev + 28
14  React                               0x000000010c6a0b1c _ZNSt3__110__function6__funcIZN8facebook5react15ObjCTurboModule23performMethodInvocationERNS2_3jsi7RuntimeEbPKcP12NSInvocationP14NSMutableArrayE3$_1NS_9allocatorISE_EEFvvEEclEv + 28
15  React                               0x000000010c6b0108 _ZNKSt3__110__function12__value_funcIFvvEEclB8de190102Ev + 60
16  React                               0x000000010c6afff8 _ZNKSt3__18functionIFvvEEclEv + 24
17  React                               0x000000010c6b00c0 ___ZN12_GLOBAL__N_129ModuleNativeMethodCallInvoker11invokeAsyncERKNSt3__112basic_stringIcNS1_11char_traitsIcEENS1_9allocatorIcEEEEONS1_8functionIFvvEEE_block_invoke + 44
18  libdispatch.dylib                   0x00000001080e3ee8 _dispatch_call_block_and_release + 24
19  libdispatch.dylib                   0x00000001080fd374 _dispatch_client_callout + 12
20  libdispatch.dylib                   0x00000001080ebfa4 _dispatch_lane_serial_drain + 888
21  libdispatch.dylib                   0x00000001080ecc0c _dispatch_lane_invoke + 428
22  libdispatch.dylib                   0x00000001080f8bf8 _dispatch_root_queue_drain_deferred_wlh + 324
23  libdispatch.dylib                   0x00000001080f815c _dispatch_workloop_worker_thread + 752
24  libsystem_pthread.dylib             0x0000000107a1ec28 _pthread_wqthread + 288
25  libsystem_pthread.dylib             0x0000000107a1da28 start_wqthread + 8

Can't show source file for stack frame 6: @objc AppDelegate.window.getter
The file path does not exist on the file system: /<compiler-generated>

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Sample Code

RNFetchBlob.ios.previewDocument(filePath);

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Expected Behavior

Document preview should open normally on iOS without Main Thread Checker warnings or crashes.

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Actual Behavior

The app throws a Main Thread Checker warning/crash while opening the document preview.

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Notes

• Issue is reproducible consistently on iOS.
• Happens with React Native 0.84.1.
• Appears related to TurboModules / New Architecture threading behavior.
• UIKit APIs may be invoked from a background thread (ReactNativeBlobUtil.queue) instead of the main thread.