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

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 on 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)
#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)

Start with the Flutter call at Ddr_flutter_engine/WebComponents/PageFileUploadView/DdrPageFileUploadView.dart lines 55 and 348, then trace MethodChannelFilePicker.getFiles and the iOS FileUtils.resolveType:withAllowedExtensions: entry at line 58. Reproduce the custom public.zip-archive request in the mixed Flutter/iOS setup. Done means file selection no longer presents from a view outside the window hierarchy and does not produce multiple_request or an unhandled exception.

Written by the indexing model from the issue text.