Introduction to the course, prerequisites, and goals

About this course

Introduction

About Module 2

Overview of the technology used in this course

About Flutter and Dart

Everything you need to start building Flutter apps

Hardware & software setup

\`flutter create\` and the Flutter project structure

Creating a Flutter app

How to build your app for emulators and physical devices

Running your app

Integrating external packages and libraries

Pub packages

Setting the app name, icon, and bundle ID

Packaging for the App Store and Google Play

Setting up your environment and packaging apps

Getting Started

About Module 3

A 5-minute introduction to the Dart language

Dart cheat sheet

Flutter in a nutshell

Setup: State

Setup: Theming

Setup: Navigation

Setup: Scaffold

Learn the basics you need to build any kind of app

Creating A Seed App

About Module 4

Text, app bar actions, and widgets that wrap every page

Creating the widget and route

Stubbing data

Widgets that wait for data

Column, Row, Padding, spacing, and alignment

Layout basics

Image

Table layouts, expansion panels, and rich text

Responsive layouts, part 2

ListView, SingleChildScrollView, and Scrollbar

Scrolling layouts

How to think about layout, infinite constraints, and unbounded size

Layout problems

TextButton, OutlinedButton, FilledButton, ElevatedButton, and button styles

Buttons

The Profile Page

About Module 5

VoiceOver on iOS

Testing accessibility on an Android emulator

TalkBack on Android

Accessibility Widgets

Making sure your app works with a screen reader

Accessibility

About Module 6

Shared preferences

HTTP requests

Login and authentication

State management with Provider and Consumer

Managing user state

Storage and HTTP

About Module 7

Building and sorting a DataTable with DataTableSource

Data tables

Using fl_chart for responsive visualizations

Charts and graphs

Building data visualizations that impress

Tables and Charts

About Module 8

Simple animations

Custom paint

Custom animations

Off-the-shelf transitions, custom drawings, and fine-tuned animations

Animations

About Module 9

flutter_test and the Flutter unit testing API

Unit tests

Testing UI interactions on individual widgets

Widget tests

Testing your entire app with automated interactions

End-to-end tests

Unit tests, widget tests, and end-to-end tests

Testing

Congratulations

Wrapping up

Flutter is a popular cross-platform development framework. It's packed with off-the-shelf features and focused
on developer ergonomics, which means you can build faster and deploy to more platforms with fewer dependencies.
Some parts of the framework will catch you by surprise, though, especially if you're used to developing for the
web or writing native apps. This course will walk you through the creation of a Flutter app from setup to
final package and help you develop a mental model that will carry you through the most common problems Flutter
devs encounter.

By the end of these 10 modules you'll have built:
- A Flutter seed project that can manage state, swap out color palettes, and handle deep links
- An accessible, error-resistant profile page that fetches data from a web API
- A responsive data table and data-driven visualizations
- A complete app ready to deploy to iPhone and Android

This course includes sample code, explained step-by-step, that you can reuse for any Flutter app you build.

It's taught by Isaac Lyman, author of _Your First Year in Code_ and Top 10 Author on The DEV Community.

After completing Line-of-Business Apps with Flutter 3, developers have the skills to build mobile apps backed by their
choice of server technologies, taking advantage of the incomparable performance, speed-to-value, and developer
experience of Flutter and Dart.

What developers are saying

Flutter

Dart

Bring your mobile app ideas to life on every device

### Build Better Mobile Apps with Flutter

Smartphones are the most popular computing devices in the world, and mobile apps are the best way to reach
technology consumers. But building fully native apps means learning two or more completely different sets of
programming languages, UI frameworks, layout systems, and developer toolkits. Other cross-platform frameworks
have tried to make this process easier, but none of them have achieved the popularity, performance, or resilience
of Flutter.

With Flutter, you'll avoid several problems you may have had with other app frameworks:

- Publish native app packages for iOS, Android, Windows, macOS, and Linux, all from a **single codebase**, without
writing a single line of native code.
- Write **faster, safer code** with the familiar syntax, type safety, and null safety of the Dart programming language.
- Flutter is an **all-in-one component library and toolkit**: spend your time building components and writing application logic
instead of fiddling with toolchain configuration and searching for 3rd-party packages.
- Never worry about the way your app looks on different devices; with Flutter's **built-in rendering engine**
and **logical pixel scaling**, your app will look the same on every screen, everywhere.

### Be Prepared for Any Challenge

Flutter is an easy-to-learn, top-rated technology for developers, but it doesn't come without gotchas. In this course, you'll
learn to breeze right through some of the hardest parts of Flutter development:

- Responsive design, complex layouts, and breakpoints
- Layout errors and infinite constraints
- Hand-drawn components
- Custom animations, tickers, and tweens
- State management and data persistence

### Start Building Real Apps Faster

This course won't waste any time teaching you what an `if` statement is. You'll be able to use the
programming experience you already have and jump straight into building mobile apps with Dart and Flutter.

Along the way, you'll build skills you can use immediately for any app you dream up:

- By the end of Module 2, you'll have already packaged a Flutter app for distribution on the iOS and Android
app stores.
- By the end of Module 3, you'll have a seed app you can use for any project.
- By the end of Module 4, you'll know how to build responsive layouts and use the most common types of widgets.
- By the end of the course, you'll have built an **accessible**, **interactive**, **server-backed** app with **custom animations**
and **three types of automated tests**.

Along the way, you'll discover Flutter's secret: it's not only the easiest way to build cross-platform mobile
and desktop apps, it's the easiest way to deliver **any* kind of technological experience, **period**. Not even the web, with
its variety of frameworks and tools, can match the development speed and polished UI of a Flutter app.

Build cross-platform iOS and Android apps faster than you thought possible

In this course you'll build a corporate app and package it for iPhone and Android from a single codebase.

Flutter is a popular and feature-rich multi-platform development toolkit, but it's got some surprises for
traditional web and desktop developers. You'll learn how to think in the Flutter way and build fast, maintainable,
visually appealing apps.

Line-of-Business Mobile Apps with Flutter and Dart

Build a secure login modal with HTTP authentication and persistent cookies

Build responsive, nested layouts and intuitive user interactions

Build fast, informative data visualizations

How to build and package apps for iOS and Android from a single codebase

Why Flutter and Dart are a perfect match for multi-platform apps

The Flutter paradigm for layout and components

How to keep your Flutter app fast and responsive

State management, server requests, accessibility, and more

The RevExSortIcon CustomPainter is set up so it knows how to draw not just an ascending or descending icon but any state in between. This will make it easier to animate between states.

The easiest way to animate a widget parameter from one value to another is with a 

. This widget doesn't offer a lot of control or flexibility, but if you just need to get from point A to point B, it's the fastest way to do it.

class RevExSortIcon extends StatelessWidget {
  final bool isAscending;

  const RevExSortIcon({
    super.key,
    required this.isAscending,
  });

  @override
  Widget build(BuildContext context) {
    final double startingValue = isAscending ? 1 : -1;
    return TweenAnimationBuilder(
      tween: Tween<double>(begin: startingValue, end: startingValue),
      duration: const Duration(milliseconds: 250),
      builder: (_, tweenValue, __) {
        return CustomPaint(
          painter: _SortIconPainter(
            ascendingness: tweenValue,
          ),
          size: const Size(16, 16),
        );
      },
    );
  }
}

TweenAnimationBuilder requires three parameters:

, I've provided the same value for both the 

 parameters; when you're using TweenAnimationBuilder, these should only be different if you want to animate something right when the widget first loads. After that, TweenAnimationBuilder will remember the most recent value in 

 function should take any value that could come out of the Tween and return a widget tree based on that value. So, as the TweenAnimationBuilder animates between values, the 

 parameter could be 1, -1, 0.5, -0.7779, 0.9999, or literally any other 

 value between 1 and -1. The CustomPaint will be rebuilt 60 times per second when the animation is running, and on each rebuild, it will draw a single "frame" of the animation. Since _SortIconPainter knows how to build in-between states with different amounts of 

Now, if you run the app, you'll see how the sort icon smoothly changes the direction it's pointing, flattening from a chevron to a straight line and then growing into a chevron again—and all this in under a hundred lines of code.

 can do non-linear transitions, too. If you'd like the transition to speed up or slow down at the end, for example, you can use the 

 parameter. Normally, you'll pass in a static field from the built-in 

 class, which provides several common transition curves like 

AnimationController, SingleTickerProviderStateMixin, and Tween

What if you want more control over your animations? With a little more code, you can control every aspect of the animation, allowing you to do things like:

Start by rewriting RevExSortIcon to use an 

. To accommodate the controller, you'll have to convert to a StatefulWidget.

class RevExSortIcon extends StatefulWidget {
  final bool isAscending;

  const RevExSortIcon({
    super.key,
    required this.isAscending,
  });

  @override
  State<RevExSortIcon> createState() => _RevExSortIconState();
}

class _RevExSortIconState extends State<RevExSortIcon>
    with SingleTickerProviderStateMixin {
  late bool isAscendingCached;
  late final AnimationController controller;
  late final Tween<double> flipTween;
  late final Animation<double> flipAnimation;

  @override
  void initState() {
    super.initState();

    isAscendingCached = widget.isAscending;

    controller = AnimationController(
      duration: const Duration(milliseconds: 250),
      vsync: this,
    );

    flipTween = Tween<double>(
      begin: isAscendingCached ? 1 : -1,
      end: isAscendingCached ? 1 : -1,
    );

    flipAnimation = controller.drive(flipTween);

    flipAnimation.addListener(() {
      setState(() {});
    });
  }

  @override
  void didUpdateWidget(RevExSortIcon oldWidget) {
    super.didUpdateWidget(oldWidget);

    if (widget.isAscending != isAscendingCached) {
      flipTween.begin = isAscendingCached ? 1 : -1;
      flipTween.end = widget.isAscending ? 1 : -1;
      controller.reset();
      controller.forward();

      isAscendingCached = widget.isAscending;
    }
  }

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

  @override
  Widget build(BuildContext context) {
    return CustomPaint(
      painter: _SortIconPainter(
        ascendingness: flipAnimation.value,
      ),
      size: const Size(16, 16),
    );
  }
}

---
title: Custom animations
description: Tweens, tickers, and chained animations
privateVideoUrl:
isPublicLesson: true
code: https://gitlab.com/fullstackio/books/newline-course-apps/isaac-lyman-line-of-business-apps-with-flutter-3/-/tree/main/App
---

The RevExSortIcon CustomPainter is set up so it knows how to draw not just an ascending or descending icon but any state in between. This will make it easier to animate between states.

## TweenAnimationBuilder

The easiest way to animate a widget parameter from one value to another is with a [`TweenAnimationBuilder`](https://api.flutter.dev/flutter/widgets/TweenAnimationBuilder-class.html). This widget doesn't offer a lot of control or flexibility, but if you just need to get from point A to point B, it's the fastest way to do it.

To use it, alter RevExSortIcon like so:

```dart
class RevExSortIcon extends StatelessWidget {
  final bool isAscending;

  const RevExSortIcon({
    super.key,
    required this.isAscending,
  });

  @override
  Widget build(BuildContext context) {
    final double startingValue = isAscending ? 1 : -1;
    return TweenAnimationBuilder(
      tween: Tween<double>(begin: startingValue, end: startingValue),
      duration: const Duration(milliseconds: 250),
      builder: (_, tweenValue, __) {
        return CustomPaint(
          painter: _SortIconPainter(
            ascendingness: tweenValue,
          ),
          size: const Size(16, 16),
        );
      },
    );
  }
}
```

TweenAnimationBuilder requires three parameters:

-   A [`Tween`](https://api.flutter.dev/flutter/animation/Tween-class.html) instance with a start and end value.
-   A [`Duration`](https://api.flutter.dev/flutter/dart-core/Duration-class.html), indicating how long the transition should take.
-   A `builder`.

For this `Tween`, I've provided the same value for both the `begin` and `end` parameters; when you're using TweenAnimationBuilder, these should only be different if you want to animate something right when the widget first loads. After that, TweenAnimationBuilder will remember the most recent value in `end` and animate whenever it changes.

The `builder` function should take any value that could come out of the Tween and return a widget tree based on that value. So, as the TweenAnimationBuilder animates between values, the `tweenValue` parameter could be 1, -1, 0.5, -0.7779, 0.9999, or literally any other `double` value between 1 and -1. The CustomPaint will be rebuilt 60 times per second when the animation is running, and on each rebuild, it will draw a single "frame" of the animation. Since \_SortIconPainter knows how to build in-between states with different amounts of `ascendingness`, this is no problem.

Now, if you run the app, you'll see how the sort icon smoothly changes the direction it's pointing, flattening from a chevron to a straight line and then growing into a chevron again—and all this in under a hundred lines of code.

:::tip

`TweenAnimationBuilder` can do non-linear transitions, too. If you'd like the transition to speed up or slow down at the end, for example, you can use the `curve` parameter. Normally, you'll pass in a static field from the built-in `Curves` class, which provides several common transition curves like `easeIn` and `easeOut`.

::::

## AnimationController, SingleTickerProviderStateMixin, and Tween

What if you want more control over your animations? With a little more code, you can control every aspect of the animation, allowing you to do things like:

-   Chaining animations together so one or more widgets animate in sequence or have overlapping animations.
-   Making animations that reverse as soon as they finish, repeat a certain number of times, or repeat indefinitely.
-   Pausing and resuming animations whenever you want.

Start by rewriting RevExSortIcon to use an [`AnimationController`](https://api.flutter.dev/flutter/animation/AnimationController-class.html). To accommodate the controller, you'll have to convert to a StatefulWidget.

```dart
class RevExSortIcon extends StatefulWidget {
  final bool isAscending;

  const RevExSortIcon({
    super.key,
    required this.isAscending,
  });

  @override
  State<RevExSortIcon> createState() => _RevExSortIconState();
}

class _RevExSortIconState extends State<RevExSortIcon>
    with SingleTickerProviderStateMixin {
  late bool isAscendingCached;
  late final AnimationController controller;
  late final Tween<double> flipTween;
  late final Animation<double> flipAnimation;

  @override
  void initState() {
    super.initState();

    isAscendingCached = widget.isAscending;

    controller = AnimationController(
      duration: const Duration(milliseconds: 250),
      vsync: this,
    );

    flipTween = Tween<double>(
      begin: isAscendingCached ? 1 : -1,
      end: isAscendingCached ? 1 : -1,
    );

    flipAnimation = controller.drive(flipTween);

    flipAnimation.addListener(() {
      setState(() {});
    });
  }

  @override
  void didUpdateWidget(RevExSortIcon oldWidget) {
    super.didUpdateWidget(oldWidget);

    if (widget.isAscending != isAscendingCached) {
      flipTween.begin = isAscendingCached ? 1 : -1;
      flipTween.end = widget.isAscending ? 1 : -1;
      controller.reset();
      controller.forward();

      isAscendingCached = widget.isAscending;
    }
  }

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

  @override
  Widget build(BuildContext context) {
    return CustomPaint(
      painter: _SortIconPainter(
        ascendingness: flipAnimation.value,
      ),
      size: const Size(16, 16),
    );
  }
}
```

There are a few new classes here to learn about.

-   [**SingleTickerProviderStateMixin**](https://api.flutter.dev/flutter/widgets/SingleTickerProviderStateMixin-mixin.html) is a class mixin that adds a TickerProvider to any StatefulWidget. A Ticker is something that notifies a listener every time a frame is drawn to the screen—theoretically, 60 times per second, though there are situations where the frame rate will drop if the processor is busy. If you need multiple Tickers (that is, you have multiple AnimationControllers), you can use [`TickerProviderStateMixin`](https://api.flutter.dev/flutter/widgets/TickerProviderStateMixin-mixin.html) instead.
-   [**AnimationController**](https://api.flutter.dev/flutter/animation/AnimationController-class.html) is the class that drives the animation. It needs a TickerProvider (that's what `vsync: this` does—`this` refers to the class itself, including any mixins) and a Duration so it knows how long the animation should last. You can use `controller.value` at any time to get a value between 0.0 and 1.0 representing the animation's progress, which will be 0.0 until you call `controller.forward()`, and then progress to 1.0 over the specified duration. You should call `dispose()` on the controller when you're done with it.
-   [**Tween&lt;T>**](https://api.flutter.dev/flutter/animation/Tween-class.html) is a class that takes values between 0.0 and 1.0 from an AnimationController and maps them to a range you specify. In this case, you want `double` values between -1.0 and 1.0, but you can set any range you want. Tweens can be used for other types of values too—any class that implements the mathematical operators `+`, `-`, and `*`, such as [`Offset`](https://api.flutter.dev/flutter/dart-ui/Offset-class.html) or [`Alignment`](https://api.flutter.dev/flutter/painting/Alignment-class.html), can be the type parameter to a Tween. There are also specialized subclasses, like [`ColorTween`](https://api.flutter.dev/flutter/animation/ColorTween-class.html) for animating between different colors and [`RectTween`](https://api.flutter.dev/flutter/animation/RectTween-class.html) for animating between differently-sized [`Rect`](https://api.flutter.dev/flutter/dart-ui/Rect-class.html) objects.
-   [**Animation&lt;T>**](https://api.flutter.dev/flutter/animation/Animation-class.html) is the superclass of `AnimationController`. It's a relatively simple class with a `status` and a `value`. The status tells us if it's stopped at the beginning, running forward, stopped at the end, or running backward; the value can be anything of type `T`. The class also provides methods for attaching listeners so we can react when the value or status changes.