main.dart

import 'package:flutter/material.dart';
import 'package:file_picker/file_picker.dart';
import 'package:flutter/services.dart';

main() => runApp(App());

class App extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return _App();
  }
}

class _App extends State<App> {
  String _fileName;
  String _path;
  Map<String, String> _paths;
  String _extension;
  bool _loadingPath = false;
  bool _multiPick = false;
  bool _hasValidMime = false;
  FileType _pickingType;
  TextEditingController _controller = new TextEditingController();

  @override
  void initState() {
    super.initState();
    _controller.addListener(() => _extension = _controller.text);
  }

  void _openFileExplorer() async {
    if (_pickingType != FileType.CUSTOM || _hasValidMime) {
      setState(() => _loadingPath = true);
      try {
        if (_multiPick) {
          _path = null;
          _paths = await FilePicker.getMultiFilePath(
              type: _pickingType, fileExtension: _extension);
        } else {
          _paths = null;
          _path = await FilePicker.getFilePath(
              type: _pickingType, fileExtension: _extension);
        }
      } on PlatformException catch (e) {
        print("Unsupported operation" + e.toString());
      }
      if (!mounted) return;
      setState(() {
        _loadingPath = false;
        _fileName = _path != null
            ? _path.split('/').last
            : _paths != null ? _paths.keys.toString() : '...';
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text("FilePickerApp"),
        ),
        body: Container(
          child: Center(
              child: Column(
            children: <Widget>[
              new Padding(
                padding: const EdgeInsets.only(top: 50.0, bottom: 20.0),
                child: new RaisedButton(
                  onPressed: () => _openFileExplorer(),
                  child: new Text("Open file picker"),
                ),
              ),
              new Builder(
                builder: (BuildContext context) => _loadingPath
                    ? Padding(
                        padding: const EdgeInsets.only(bottom: 10.0),
                        child: const CircularProgressIndicator())
                    : _path != null || _paths != null
                        ? new Container(
                            padding: const EdgeInsets.only(bottom: 30.0),
                            height: MediaQuery.of(context).size.height * 0.50,
                            child: new Scrollbar(
                                child: new ListView.separated(
                              itemCount: _paths != null && _paths.isNotEmpty
                                  ? _paths.length
                                  : 1,
                              itemBuilder: (BuildContext context, int index) {
                                final bool isMultiPath =
                                    _paths != null && _paths.isNotEmpty;
                                final String name = 'File $index: ' +
                                    (isMultiPath
                                        ? _paths.keys.toList()[index]
                                        : _fileName ?? '...');
                                final path = isMultiPath
                                    ? _paths.values.toList()[index].toString()
                                    : _path;

                                return new ListTile(
                                  title: new Text(
                                    name,
                                  ),
                                  subtitle: new Text(path),
                                );
                              },
                              separatorBuilder:
                                  (BuildContext context, int index) =>
                                      new Divider(),
                            )),
                          )
                        : new Container(),
              ),
            ],
          )),
        ),
      ),
    );
  }
}

pubspec.yaml

name: filepickerapp
description: A new Flutter project.

# The following defines the version and build number for your application.
# A version number is three numbers separated by dots, like 1.2.43
# followed by an optional build number separated by a +.
# Both the version and the builder number may be overridden in flutter
# build by specifying --build-name and --build-number, respectively.
# In Android, build-name is used as versionName while build-number used as versionCode.
# Read more about Android versioning at https://developer.android.com/studio/publish/versioning
# In iOS, build-name is used as CFBundleShortVersionString while build-number used as CFBundleVersion.
# Read more about iOS versioning at
# https://developer.apple.com/library/archive/documentation/General/Reference/InfoPlistKeyReference/Articles/CoreFoundationKeys.html
version: 1.0.0+1

environment:
  sdk: ">=2.1.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter

  # The following adds the Cupertino Icons font to your application.
  # Use with the CupertinoIcons class for iOS style icons.
  cupertino_icons: ^0.1.2
  file_picker: ^1.4.2

dev_dependencies:
  flutter_test:
    sdk: flutter


# For information on the generic Dart part of this file, see the
# following page: https://dart.dev/tools/pub/pubspec

# The following section is specific to Flutter.
flutter:

  # The following line ensures that the Material Icons font is
  # included with your application, so that you can use the icons in
  # the material Icons class.
  uses-material-design: true

  # To add assets to your application, add an assets section, like this:
  # assets:
  #  - images/a_dot_burr.jpeg
  #  - images/a_dot_ham.jpeg

  # An image asset can refer to one or more resolution-specific "variants", see
  # https://flutter.dev/assets-and-images/#resolution-aware.

  # For details regarding adding assets from package dependencies, see
  # https://flutter.dev/assets-and-images/#from-packages

  # To add custom fonts to your application, add a fonts section here,
  # in this "flutter" section. Each entry in this list should have a
  # "family" key with the font family name, and a "fonts" key with a
  # list giving the asset and other descriptors for the font. For
  # example:
  # fonts:
  #   - family: Schyler
  #     fonts:
  #       - asset: fonts/Schyler-Regular.ttf
  #       - asset: fonts/Schyler-Italic.ttf
  #         style: italic
  #   - family: Trajan Pro
  #     fonts:
  #       - asset: fonts/TrajanPro.ttf
  #       - asset: fonts/TrajanPro_Bold.ttf
  #         weight: 700
  #
  # For details regarding fonts from package dependencies,
  # see https://flutter.dev/custom-fonts/#from-packages

file_picker: 1.4.2