Flutter : A procedure runs well in debug mode but not after release, why?

Question

My project works everything fine in debug mode but After release, everything works except one procedure.

Here is the procedure :

 Future<void> downloadFile() async{
Dio dio = Dio();

var directory = await getApplicationDocumentsDirectory();
await dio.download(bookUrl, "${directory.path}/$className + $bookName.pdf",
onReceiveProgress: (rec, total){
  setState(() {
    downloading = true;
    percentage = ((rec/total) * 100).toStringAsFixed(0)+'%';
  });
}

);

setState(() {
  downloading = false;
  percentage = 'Download Completed';
});

}

Here is the error message I've got when Release app runs :

E/flutter (25796): [ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: DioError [DioErrorType.DEFAULT]: SocketException: Failed host lookup: 'www.ets.org' (OS Error: No address associated with hostname, errno = 7) E/flutter (25796): #0 Dio._makeRequest (package:dio/src/dio.dart:799) E/flutter (25796): E/flutter (25796): #1 Dio._request.. (package:dio/src/dio.dart:711) E/flutter (25796): #2 _rootRunUnary (dart:async/zone.dart:1132) E/flutter (25796): #3 _CustomZone.runUnary (dart:async/zone.dart:1029) E/flutter (25796): #4 _FutureListener.handleValue (dart:async/future_impl.dart:126) E/flutter (25796): #5
Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:639) E/flutter (25796): #6
Future._propagateToListeners (dart:async/future_impl.dart:668) E/flutter (25796): #7 Future._complete (dart:async/future_impl.dart:473) E/flutter (25796): #8
_SyncCompleter.complete (dart:async/future_impl.dart:51) E/flutter (25796): #9 _AsyncAwaitCompleter.complete. (dart:async-patch/async_patch.dart:33) E/flutter (25796): #10
_rootRun (dart:async/zone.dart:1120) E/flutter (25796): #11 _CustomZone.run (dart:async/zone.dart:1021) E/flutter (25796): #12 _CustomZone.runGuarded (dart:async/zone.dart:923) E/flutter (25796): #13 _CustomZone.bindCallbackGuarded. (dart:async/zone.dart:963) E/flutter (25796): #14 _rootRun (dart:async/zone.dart:1124) E/flutter (25796): #15 _CustomZone.run (dart:async/zone.dart:1021) E/flutter (25796): #16
_CustomZone.runGuarded (dart:async/zone.dart:923) E/flutter (25796): #17 _CustomZone.bindCallbackGuarded. (dart:async/zone.dart:963) E/flutter (25796): #18 _microtaskLoop (dart:async/schedule_microtask.dart:41) E/flutter (25796): #19
_startMicrotaskLoop (dart:async/schedule_microtask.dart:50)

Solution 1

SocketException: Failed host lookup: 'www.ets.org' (OS Error: No address associated with hostname, errno = 7)

It seems you cannot connect to this host. Could it be that you need network permissions for your app?

Edit: see OP's answer below for the specific line of code: https://stackoverflow.com/a/56921201/679553

Solution 2

make sure you have

<uses-permission android:name="android.permission.INTERNET" />

in your app's android/app/src/main/AndroidManifest.xml

Comments

[mrb]

I don't know about this. this is the only procedure that gives error after release.

[mrb]

I did. Thank you.