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

Flutter has a heap of off-the-shelf widgets that render almost any UI you could ever need in a line-of-business app. But for those rare cases where nothing seems to fit, you have the option of painting something to the screen manually. If you've ever written SVG paths by hand, this process will be familiar to you.

One feature that's missing from PaginatedDataTable is the ability to customize the sort icon. There's an 

 for that functionality, but it's been waiting in the backlog for a couple of years now. Someday, someone will contribute a PR that fixes it. But for now, you can use a workaround.

// overview.page.dart
class _TransactionTableState extends State<_TransactionTable> {
  late _TransactionDataSource tableData;

  @override
  void initState() {
    super.initState();
    tableData = _TransactionDataSource(widget.transactions, context);
    tableData.addListener(() => mounted ? setState(() {}) : null);
  }

  @override
  Widget build(BuildContext context) {
    return PaginatedDataTable(
      columns: tableData.getColumns(),
      source: tableData,
    );
  }
}

This prevents the sort icon from showing, but now the table won't switch between ascending and descending sort when you tap a column header more than once. You can fix that with a bit of extra logic in the 

// overview.page.dart
class _TransactionDataSource extends DataTableSource {
// ...
  Function(int, bool) handleSort(
      int Function(RevExTransaction a, RevExTransaction b) compare) {
    return (ix, ascending) {
      if (ix == sortIndex) {
        sortAscending = !sortAscending;
      } else {
        sortAscending = ascending;
      }

      sortIndex = ix;

      transactions.sort(compare);
      if (!sortAscending) {
        transactions = transactions.reversed.toList();
      }
      notifyListeners();
    };
  }
// ...
}

Now there's an empty space where the sort indicator would be, and you have all the information you need to create your own.

To draw custom objects on the screen, write a class that extends 

 uses a canvas, paths, and paints to draw whatever you like. Let's draw a chevron pointing down.

import 'package:flutter/material.dart';

class RevExSortIcon extends StatelessWidget {
  RevExSortIcon({super.key});

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

class _SortIconPainter extends CustomPainter {
  _SortIconPainter();

  @override
  void paint(Canvas canvas, Size size) {
    const chevronPoints = [
      [0.1, 0.3],
      [0.5, 0.7],
      [0.9, 0.3],
    ];

    var path = Path();

    path.moveTo(
        size.width * chevronPoints[0][0], size.height * chevronPoints[0][1]);
    path.lineTo(
        size.width * chevronPoints[1][0], size.height * chevronPoints[1][1]);
    path.lineTo(
        size.width * chevronPoints[2][0], size.height * chevronPoints[2][1]);

    var paint = Paint();
    paint.color = Colors.black;
    paint.strokeWidth = 1.5;
    paint.style = PaintingStyle.stroke;

    canvas.drawPath(path, paint);
  }

  @override
  bool shouldRepaint(_SortIconPainter oldDelegate) => true;
}

---
title: Custom paint
description: Line-drawn widgets with CustomPainter
privateVideoUrl: 
isPublicLesson: true
code: https://gitlab.com/fullstackio/books/newline-course-apps/isaac-lyman-line-of-business-apps-with-flutter-3/-/tree/main/App
---

Flutter has a heap of off-the-shelf widgets that render almost any UI you could ever need in a line-of-business app. But for those rare cases where nothing seems to fit, you have the option of painting something to the screen manually. If you've ever written SVG paths by hand, this process will be familiar to you.

## Preparing for a new sort icon

One feature that's missing from PaginatedDataTable is the ability to customize the sort icon. There's an [issue filed in GitHub](https://github.com/flutter/flutter/issues/91801) for that functionality, but it's been waiting in the backlog for a couple of years now. Someday, someone will contribute a PR that fixes it. But for now, you can use a workaround.

You can start by removing the `sortColumnIndex` and `sortAscending` parameters from your `PaginatedDataTable` parameters:

```dart
// overview.page.dart
class _TransactionTableState extends State<_TransactionTable> {
  late _TransactionDataSource tableData;

  @override
  void initState() {
    super.initState();
    tableData = _TransactionDataSource(widget.transactions, context);
    tableData.addListener(() => mounted ? setState(() {}) : null);
  }

  @override
  Widget build(BuildContext context) {
    return PaginatedDataTable(
      columns: tableData.getColumns(),
      source: tableData,
    );
  }
}
```

This prevents the sort icon from showing, but now the table won't switch between ascending and descending sort when you tap a column header more than once. You can fix that with a bit of extra logic in the `handleSort` method:

```dart
// overview.page.dart
class _TransactionDataSource extends DataTableSource {
// ...
  Function(int, bool) handleSort(
      int Function(RevExTransaction a, RevExTransaction b) compare) {
    return (ix, ascending) {
      if (ix == sortIndex) {
        sortAscending = !sortAscending;
      } else {
        sortAscending = ascending;
      }

      sortIndex = ix;

      transactions.sort(compare);
      if (!sortAscending) {
        transactions = transactions.reversed.toList();
      }
      notifyListeners();
    };
  }
// ...
}
```

Now there's an empty space where the sort indicator would be, and you have all the information you need to create your own.

## CustomPaint

To draw custom objects on the screen, write a class that extends [`CustomPainter`](https://api.flutter.dev/flutter/rendering/CustomPainter-class.html), then provide it to a [`CustomPaint`](https://api.flutter.dev/flutter/widgets/CustomPaint-class.html) widget. `CustomPainter` uses a canvas, paths, and paints to draw whatever you like. Let's draw a chevron pointing down.

Create a new file at `lib/widgets/sort_icon.dart`, then add a `CustomPaint` widget and class extending `CustomPainter`:

```dart
import 'package:flutter/material.dart';

class RevExSortIcon extends StatelessWidget {
  RevExSortIcon({super.key});

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

class _SortIconPainter extends CustomPainter {
  _SortIconPainter();

  @override
  void paint(Canvas canvas, Size size) {
    const chevronPoints = [
      [0.1, 0.3],
      [0.5, 0.7],
      [0.9, 0.3],
    ];

    var path = Path();

    path.moveTo(
        size.width * chevronPoints[0][0], size.height * chevronPoints[0][1]);
    path.lineTo(
        size.width * chevronPoints[1][0], size.height * chevronPoints[1][1]);
    path.lineTo(
        size.width * chevronPoints[2][0], size.height * chevronPoints[2][1]);

    var paint = Paint();
    paint.color = Colors.black;
    paint.strokeWidth = 1.5;
    paint.style = PaintingStyle.stroke;

    canvas.drawPath(path, paint);
  }

  @override
  bool shouldRepaint(_SortIconPainter oldDelegate) => true;
}
```

The magic here is in the [`Path`](https://api.flutter.dev/flutter/dart-ui/Path-class.html) instance. You can use its `moveTo` method to jump to the starting point of the chevron, then the `lineTo` method to draw the downward and upward strokes. A Path can also draw arcs, bezier curves, and a handful of basic shapes. I like to plot out my shape as if I were drawing it on a square 1 unit wide and 1 unit tall so I can think of everything in terms of percentages. Then, since the `paint` method provides the actual size of the space available to draw in, I can multiply my points by `size.width` and `size.height` to scale the shape correctly.