Introduction to Flutter for Cross-Platform Apps

1. Introduction

Goal of this tutorial: This tutorial aims to provide a beginner-friendly introduction to Flutter, a UI toolkit developed by Google. By the end of this tutorial, you will be able to create your first cross-platform app.

What you will learn:
- Basics of Flutter
- How to set up a Flutter development environment
- How to create a simple Flutter app
- Understanding of Dart programming language

Prerequisites:
- Basic understanding of programming concepts
- Familiarity with object-oriented programming can be helpful but not mandatory

2. Step-by-Step Guide

Understanding Flutter: Flutter is a UI toolkit that allows developers to create natively compiled applications for mobile, web, and desktop from a single codebase. It uses the Dart programming language.

Setting up Flutter:
- Visit the official Flutter installation page (https://flutter.dev/docs/get-started/install)
- Follow the instructions based on your OS (Windows, MacOS, Linux) to install Flutter and Dart

Creating your first Flutter app:
- Open your terminal or command prompt
- Navigate to the directory where you want to create your new Flutter project
- Run the command flutter create my_app (replace 'my_app' with your preferred app name)
- Navigate into the new project directory with cd my_app
- Finally, you can run your app with flutter run

Understanding Dart: Dart is the programming language used in Flutter. It is object-oriented and strongly typed. If you are familiar with languages like Java or C#, Dart should feel quite familiar.

3. Code Examples

Creating a simple Flutter app:

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // This is the root of your application.
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('My First Flutter App'),
        ),
        body: Center(
          child: Text('Hello, Flutter!'),
        ),
      ),
    );
  }
}

In this example, we are creating a simple Flutter app that displays a text 'Hello, Flutter!' at the center of the screen. Here's a breakdown of the code:

• import 'package:flutter/material.dart'; This line imports the Material library, which provides us with a lot of pre-defined UI widgets that we can use in our app.
• void main() => runApp(MyApp()); This is the main function of the app, where the execution starts. runApp() function takes your custom Widget and makes it the root of the widget tree.
• class MyApp extends StatelessWidget {} Here we define MyApp widget. It extends StatelessWidget which makes the widget immutable.
• Widget build(BuildContext context) {} Every Widget has a build method which describes what to display.
• MaterialApp is a predefined widget in Flutter which provides a number of functionalities such as navigation, theming, font styles, etc.
• Scaffold is another predefined widget that follows the Material Design guidelines. It offers a number of API's like appBar, body, floatingActionButton, etc.
• AppBar is a widget that contains the toolbar at the top of the screen with an optional title.
• Center is a widget that aligns its child at the center of the screen.
• Text is a widget that displays a string of text with single style.

When you run this code, you will see a screen with an AppBar titled 'My First Flutter App' and a text 'Hello, Flutter!' at the center of the screen.

4. Summary

In this tutorial, we have covered the basics of Flutter and Dart, set up a development environment, and created a simple Flutter app. The next steps for learning would be to dive deeper into Flutter widget tree, state management, and exploring more complex widgets. Here are some additional resources:
- Official Flutter Documentation: https://flutter.dev/docs
- Dart Language Guide: https://dart.dev/guides
- Flutter Widget Catalog: https://flutter.dev/docs/development/ui/widgets

5. Practice Exercises

Exercise 1:
Create an app with an AppBar titled 'Exercise 1' and a body with a text 'This is my first exercise'.

Exercise 2:
Modify the first exercise to include a FloatingActionButton that, when pressed, changes the text in the body to 'Button Pressed'.

Exercise 3:
Create an app that includes an AppBar and a ListView with 10 list items, each displaying 'List Item: n', where n is the respective list index.

The solutions and explanations to these exercises are left as an exercise for the reader to help them practice and learn. As a tip, remember to explore the Flutter widget catalog to find out which widgets you can use to solve the exercises. Happy coding!