Warning: Attempt to present <UIDocumentPickerViewController: 0x12a5bdb70> on <BaseNavigationController: 0x104875800> whose view is not in the window hierarchy!

[284082529]

IOS and flutter are mixed development, and flutter is integrated into the IOS project. Find the following problem.
How to solve this problem, thank you.

**** Custom file type supported: public.zip-archive

• +[FileUtils resolveType:withAllowedExtensions:] [Line 58]
  2020-08-11 10:55:29.004708+0800 Fresenius[17522:10638996] Warning: Attempt to present <UIDocumentPickerViewController: 0x12a5a6ef0> on <BaseNavigationController: 0x104875800> whose view is not in the window hierarchy!
  2020-08-11 10:55:29.326806+0800 Fresenius[17522:10639118] flutter: [MethodChannelFilePicker] Platform exception: PlatformException(multiple_request, Cancelled by a second request, null)
  2020-08-11 10:55:29.327257+0800 Fresenius[17522:10639118] [VERBOSE-2:ui_dart_state.cc(157)] Unhandled Exception: PlatformException(multiple_request, Cancelled by a second request, null)
  #0 StandardMethodCodec.decodeEnvelope (package:flutter/src/services/message_codecs.dart:569:7)
  Support HTTP headers for authentication #1 MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:156:18)

#2 MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:329:12) #3 MethodChannelFilePicker._getPath (package:file_picker_platform_interface/method_channel_file_picker.dart:66:39) #4 MethodChannelFilePicker.getFiles (package:file_picker_platform_interface/method_channel_file_picker.dart:25:7) #5 FilePicker.getMultiFile (package:file_picker/file_picker.dart:84:65) #6 _DdrPageFileUploadViewState.obtainFile (package:ddr_flutter_engine/WebComponents/PageFileUploadView/DdrPageFileUploadView.dart:55:41) #7 _DdrPageFileUploadViewState.build. (package:ddr_flutter_engine/WebComponents/PageFileUploadView/DdrPageFileUploadView.dart:348:13) #8 _InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:779:19) #9 _InkResponseState.build. (package:flutter/src/material/ink_well.dart:862:36) #10 GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:182:24) #11 TapGestureRecognizer.handleTapUp (package:flutter/src/gestures/tap.dart:504:11) #12 BaseTapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:282:5) #13 BaseTapGestureRecognizer.acceptGesture (package:flutter/src/gestures/tap.dart:254:7) #14 GestureArenaManager.sweep (package:flutter/src/gestures/arena.dart:156:27) #15 GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:222:20) #16 GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:198:22) #17 GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:156:7) #18 GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:102:7) #19 GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:86:7) #20 _rootRunUnary (dart:async/zone.dart:1196:13) #21 _CustomZone.runUnary (dart:async/zone.dart:1085:19) #22 _CustomZone.runUnaryGuarded (dart:async/zone.dart:987:7) #23 _invoke1 (dart:ui/hooks.dart:275:10) #24 _dispatchPointerDataPacket (dart:ui/hooks.dart:184:5)