provider_simple_dialog_file

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
const Color darkBlue = Color.fromARGB(255, 18, 32, 47);

void main() {
  runApp(
    Provider(
      create:  (_) => FileProcessingService(),
      child: MyApp()
    )
  );
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
          child: MainPageTest(),
        ),
      ),
    );
  }
}

class MainPageTest extends StatefulWidget {
  const MainPageTest({Key? key}) : super(key: key);

  @override
  State<MainPageTest> createState() => _MainPageTestState();
}

class _MainPageTestState extends State<MainPageTest> {
  final double _buttonTextSize = 20.0;
  final double _widgetWidth = 200.0;

  List<String>? _files;

  late final TextEditingController _textController;

  @override
  void initState() {
    super.initState();
    _textController = TextEditingController();
  }

  @override
  void dispose() {
    _textController.dispose();
    super.dispose();
  }

  List<String> pickFiles() {
     return [
       'FileName1.png',
       'AnotherFile2.jpg',
       'ThisIsAnotherfile.mp3',
       'LastFileInTheList.mp4'
     ];
  }

  @override
  Widget build(BuildContext context) {
    
    var fileService = Provider.of<FileProcessingService>(context, listen: false);
    
    return Center(
      child: Column(
        children: [
          Padding(
            padding: const EdgeInsets.all(8.0),
            child: SizedBox(
              width: _widgetWidth,
              child: TextButton(
                onPressed: () {
                  fileService.filesToPic.value = pickFiles();
                },
                child: Padding(
                  padding: const EdgeInsets.symmetric(vertical: 12.0),
                  child: Column(
                    children: [
                      Text(
                        'Choose Files',
                        style: TextStyle(
                          fontSize: _buttonTextSize,
                        ),
                      ),
                      ValueListenableBuilder<List<String>>(
                        valueListenable: fileService.filesToPic,
                        builder: (context, value, child) {

                          if (value.isEmpty) {
                            return const Text('no files');
                          }
                          
                          return Text('${value.length} files picked');
                        }
                      )
                    ] 
                  ),
                ),
              ),
            ),
          ),
          Padding(
            padding: const EdgeInsets.symmetric(horizontal: 12.0),
            child: SizedBox(
              width: _widgetWidth,
              child: TextButton(
                onPressed: () async {
                  await EnigmaTest().encrypt(fileService.filesToPic.value, context);
                  MyLoadingAlertDialog.showLoadingAlert(context, fileService.filesToPic.value.length);
                },
                child: Padding(
                  padding: const EdgeInsets.symmetric(vertical: 12.0),
                  child: Text(
                    'Encrypt',
                    style: TextStyle(
                      fontSize: _buttonTextSize,
                    ),
                  ),
                ),
              ),
            ),
          ),
        ],
      ),
    );
  }
}

class EnigmaTest {
  Future<void> encrypt(List<String> files, BuildContext context) async {
    
    // THIS IS FAKING YOUR ENCRYPTION LOGIC/ REPLACE WITH YOUR LOGIC
    // AND MAKE SURE THAT, AS FILES ARE PROCESSED,
    // YOU CALL notifyFileBeingProcessed SO THE DIALOG GETS NOTIFIED
    var fileService = Provider.of<FileProcessingService>(context, listen: false);
    
    for(var i = 0; i < files.length; i++) {
      Future.delayed(Duration(seconds: i * 1), () {
        fileService.notifyFileBeingProcessed(files[i]);
      });
    }
  }
}

class MyLoadingAlertDialog {
  static showLoadingAlert(BuildContext context, int totalFiles) {
    
    var fileService = Provider.of<FileProcessingService>(context, listen: false);
    
    showDialog(
      context: context,
      builder: (context) {
        return AlertDialog(
          title: const Text('Progress'),
          content: Column(
            mainAxisSize: MainAxisSize.min,
            children: [
              
              Padding(
                padding: const EdgeInsets.all(4.0),
                child: ValueListenableBuilder<String>(
                   valueListenable: fileService.fileName,
                   builder: (context, value, child) {
                     
                     var numOfFiles = fileService.numOfFilesProcessed;
                     
                     if (numOfFiles == totalFiles) {
                       return const Text('All Files done!');
                     }
                     
                     if (value.isEmpty) {
                       return const Text('No value being processed!');
                     }
                     return Column(
                        children: [
                          Text(
                            'currently encrypting $value...',
                            style: const TextStyle(
                              fontSize: 10.0, fontStyle: FontStyle.italic),
                          ),
                          SizedBox(
                            width: double.infinity,
                            child: LinearProgressIndicator(value: fileService.numOfFilesProcessed * 0.25),
                          ),
                        ]
                     );
                   }
                ),
              ),
            ],
          ),
        );
      },
    );
  }
}

// SIMPLE SERVICE CLASS TO SERVE AS THE COMMUNICATION BETWEEN WIDGETS
class FileProcessingService {
  
  // ValueNotifiers trigger notifications
  // whoever is listening on these properties (i.e. filesToPic, fileName)
  // will rebuild, showing the current state of their values
  
  ValueNotifier<List<String>> filesToPic = ValueNotifier([]);
  ValueNotifier<String> fileName = ValueNotifier('');
  int numOfFilesProcessed = 0;
  
  // helper method to update the files and increment the count
  void notifyFileBeingProcessed(String f) {
    numOfFilesProcessed++;
    fileName.value = f;
  }
}