Flutter

Introduction

Why Flutter created in 2017

• Compiles to native, JIT and Ahead of Time
• Fast Development
• Single Code Base
• Uses Dart

Resources is https://github.com/simoales/flutter

Installation

Flutter

You can switch versions of flutter using the channel option where there are options of master, dev, beta etc. See https://github.com/flutter/flutter/wiki/Flutter-build-release-channels

sudo snap install flutter --classic
sudo snap install flutter-gallery
flutter channel dev
flutter upgrade
flutter config --enable-linux-desktop

You will need to specify the path to android studio

flutter config --android-studio-dir="/opt/android-studio-4.1/android-studio"

Android Studio

For Android Studio the flutter SDK will be in /home/(username)/snap/flutter/common/flutter

Flutter doctor

You can run flutter doctor to see if all went well. This is what I got

flutter doctor
[✓] Flutter (Channel dev, 1.25.0-8.0.pre, on Linux, locale en_NZ.UTF-8)
[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
[✓] Linux toolchain - develop for Linux desktop
[!] Android Studio (not installed)
[✓] VS Code (version 1.52.0)
[✓] Connected device (1 available)

Creating a Project

In VS Code run flutter doctor and then flutter new project. Project names must be in lower case. e.g. hello_flutter. This opens a new VS Code with the project. The import contains the widgets to use and the rest just configures the widgets on the screen. I.E. Text is like a <Text /> tag in react or angular.

import 'package:flutter/material.dart';

void main() {
  runApp(Center(
    child: Text("Fred Was Ere",
        textDirection: TextDirection.ltr,
        style: TextStyle(backgroundColor: Colors.blue)),
  ));
}

A Bigger Example

So a bigger example might be

import 'package:flutter/material.dart';

void main() {
  runApp(MaterialApp(
    title: "My lovely App",
    home: Scaffold(
      appBar: AppBar(
        title: Text("App Bar Title"),
      ),
      body: Material(
        color: Colors.deepPurple,
        child: Center(
          child: Text(
            "Fred Was Ere",
            textDirection: TextDirection.ltr,
            style: TextStyle(color: Colors.white, fontSize: 36.0),
          ),
        ),
      ),
    ),
  ));
}

Classes

Things are getting a big large so we need to break the code down. We do this by writing our own classes. We can derive a class from StatelessWidget to do this.

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: "My lovely App",
      home: Scaffold(
        appBar: AppBar(
          title: Text("App Bar Title"),
        ),
        body: Material(
          color: Colors.deepPurple,
          child: Center(
            child: Text(
              "Fred Was Ere",
              textDirection: TextDirection.ltr,
              style: TextStyle(color: Colors.white, fontSize: 36.0),
            ),
          ),
        ),
      ),
    );
  }
}

Fat Arrow

Dart supports the fat arrow approach so we can so

import './screens/home.dart';

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

Can become

import './screens/home.dart';

void main() => runApp(MyWidget());

Adding Logic

No surprises here. We can add functions within the class declaration.

import 'package:flutter/material.dart';

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Material(
      color: Colors.deepPurple,
      child: Center(
        child: Text(
          sayHello(),
          textDirection: TextDirection.ltr,
          style: TextStyle(color: Colors.white, fontSize: 36.0),
        ),
      ),
    );
  }

  String sayHello() {
    var hello;
    DateTime now = DateTime.now();
    if (now.hour < 12) {
      hello = "Good Morning";
    } else if (now.hour < 18) {
      hello = "Good Afternoon";
    } else {
      hello = "Good Evening";
    }
    return hello;
  }
}

Basic Widgets and Concepts

The basic widgets and Concepts are

• Container
• Text
• Row & Column
• Image
• RaisedButton
• AlertDialog
• Box Constraints
• Size, Margin and Padding