Flutter: Permission denied writing file

final Io.Directory systemTempDir = Io.Directory.systemTemp; seems to not work in release mode.

I had to do as below:

Directory tempDir = await getTemporaryDirectory();
final File file = File("${tempDir.path}/$fileName");

getTemporaryDirectory() is provided by path_provider.

There may be a problem with the paths depending on the device being used. Have a look at the path_provider plugin: https://pub.dartlang.org/packages/path_provider

There's a good write-up of how to read and write files in the Flutter Cookbook on flutter.io: https://flutter.io/cookbook/persistence/reading-writing-files/

In Android Q, just add the Following Lines in AndroidManifest file:

 <application
      android:requestLegacyExternalStorage="true"