Indicador de progreso en Flutter

Flutter CircularProgressIndicator es un widget material que indica que la aplicación está ocupada. En primer lugar, creamos un nuevo proyecto utilizando Visual Studio Code (IDE) con el nombre «indicador de progreso». Puedes elegir cualquier nombre.

Pasos:

1. Invoque Ver > Paleta de comandos.

2. Escriba «flutter» y seleccione Flutter: New Project.

3. Ingrese un nombre de proyecto y presione Entrar.

4. Cree el directorio principal para la nueva carpeta del proyecto.

Actualice el complemento Progress_dialog: ^ 1.2.0 en el directorio pubspec.yaml debería verse como a continuación

name: progressindicator
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
  progress_dialog: ^1.2.0

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

Ahora actualice el paquete flutter del cuadro de diálogo de progreso.

Cree un archivo con el nombre main.dart como se muestra a continuación:

import 'package:flutter/material.dart';
import 'package:progress_dialog/progress_dialog.dart';
   
ProgressDialog pr;
   
void main() {
  runApp(MaterialApp(
    home: FirstScreen(),
  ));
}
   
class FirstScreen extends StatefulWidget {
  @override
  _FirstScreenState createState() => _FirstScreenState();
}
   
class _FirstScreenState extends State {
  ProgressDialog pr;
   
  @override
  // Add the CSS details of the page
  Widget build(BuildContext context) {
    pr = new ProgressDialog(context);
    pr.style(
          message: 'processing',
          borderRadius: 8.0,
          backgroundColor: Colors.white,
          progressWidget: CircularProgressIndicator(),
          elevation: 8.0,
          insetAnimCurve: Curves.easeInOut,
          progress: 0.0,
          maxProgress: 100.0,
          progressTextStyle: TextStyle(
            color: Colors.white, fontSize: 13.0,
            fontWeight: FontWeight.w400),
          messageTextStyle: TextStyle(
            color: Colors.white, fontSize: 19.0,
            fontWeight: FontWeight.w600)
        );
   
    return Scaffold(
      appBar: AppBar(
        // Define the design
          title: const Text('GeeksForGeeks'),
          backgroundColor: Colors.green,),
      body: Center(
          
        child: RaisedButton(
          child: Text('Click here..',
              style: TextStyle(color: Colors.white)),
          color: Colors.green,
          onPressed: () {
            pr.show();
            Future.delayed(Duration(seconds: 2)).then((value) {
              pr.hide().whenComplete(() {
                Navigator.of(context).push(MaterialPageRoute(
                    builder: 
                  (BuildContext context) => SecondScreen()));
              });
            });
          },
        ),
      ),
    );
  }
}
   
class SecondScreen extends StatefulWidget {
  @override
  _SecondScreenState createState() => _SecondScreenState();
}
   
class _SecondScreenState extends State {
  @override
  // Define the child 
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: RaisedButton(
          onPressed: () => Navigator.of(context).pop(),
          child: Text('Back',
              style: TextStyle(color: Colors.white)),
          color: Colors.green,
        ),
      ),
    );
  }
}

Producción :

El código completo está disponible en  github.com/progressIndicator