Week 3: Flutter Basics

Overview

This week we will be learning the basics of Flutter. Flutter is a cross-platform mobile app development framework that allows you to write code once and deploy it to both iOS and Android. Flutter uses the Dart programming language, which is similar to Java and JavaScript.

Learning Objectives

By the end of this week, you should be able to:

Create a Flutter project
Run a Flutter project on an emulator or physical device
Use the Flutter documentation to learn about widgets
Create a simple Flutter app with one page using stateless widgets
file management

Resources

Here are some resources to help you with this week's assignment:

Project Overview

You will create a simple weather app that displays the current weather conditions for a given location. This will only be front-end development, so you will not need to worry about fetching data from an API.

Setup And Tutorial

1. Setup

Fork this repository
Clone your forked repository to your computer
Open the folder you just cloned in VS Code
- Extensions to install:
  - Dart
  - Flutter
  - Awesome Flutter Snippets
  - Flutter Widget Snippets
  - Pubspec Assist
  - Material Icon Theme
Android Virtual device
- Install Android Studio
- Open Android Studio
- Click on the AVD Manager icon
- Create a new virtual device
- Run the virtual device
Run the following command:
- flutter doctor
  - This will tell you if you have any issues with your Flutter installation
- flutter devices
  - This will tell you if you have any issues with your Android Virtual Device
- flutter pub get
  - This will install all of the dependencies in your pubspec.yaml file
- flutter run
  - This will run your app on your Android Virtual Device

2. Flutter Basic Widgets

Go into the lib folder and open main.dart

Looking at the code

import 'package:flutter/material.dart';

void main() {
  runApp(const MainApp());
}

class MainApp extends StatelessWidget {
  const MainApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: Scaffold(
        body: Center(
          child: Text('Hello World!'),
        ),
      ),
    );
  }
}

The main() function is the entry point of the app. It is where the app starts executing.
The runApp() function takes a widget and runs it. In this case, we are running the MainApp widget.
The MainApp widget is a stateless widget. Stateless widgets are immutable, meaning that their properties can't change—all values are final. This widget does not have to be called MainApp, but it is good practice to name your widget the same as your file.
The MainApp widget has a build() method that returns a widget. This is the widget that will be displayed when the app is launched.
The MainApp widget returns a MaterialApp widget. The MaterialApp widget is a widget that provides a framework for implementing the basic material design layout of your app.

MaterialApp

MaterialApp(
    title: 'Weather App',
    theme: ThemeData(
      primarySwatch: Colors.blue,
    ),
    home: const Scaffold(),
    debugShowCheckedModeBanner: false,
);

The MaterialApp widget is the root widget of your app. It is what allows you to use Material Design components in your app.
The MaterialApp widget has a home property that takes a widget. This is the widget that will be displayed when the app is launched.
The MaterialApp widget also has a theme property that takes a ThemeData object. This is where you can customize the theme of your app.
The MaterialApp widget also has a title property that takes a string. This is the title of your app that will be displayed in the app switcher.
The MaterialApp widget also has a debugShowCheckedModeBanner property that takes a boolean. This is whether or not you want the debug banner to be displayed in the top right corner of your app.

Scaffold

Scaffold(
    appBar: AppBar(
      title: const Text('Weather App'),
    ),
    body: const Center(
      child: Text('Hello World!'),
    ),
    floatingActionButton: FloatingActionButton(
      onPressed: () {},
      child: const Icon(Icons.add),
    ),
);

The Scaffold widget is a widget that provides a framework for implementing the basic material design layout of your app.
The Scaffold widget has a body property that takes a widget. This is the widget that will be displayed in the body of the scaffold.
The Scaffold widget also has an appBar property that takes a AppBar widget. This is the widget that will be displayed in the app bar of the scaffold.
The Scaffold widget also has a floatingActionButton property that takes a widget. This is the widget that will be displayed in the bottom right corner of the scaffold.

Row

Row(
  mainAxisAlignment: MainAxisAlignment.center,
  children: const [
    Text('Hello'),
    Text('World'),
  ],
);

The Row widget is a widget that displays its children in a horizontal array.
The Row widget has a mainAxisAlignment property that takes a MainAxisAlignment enum. This is how the children of the row will be aligned.
The Row widget also has a crossAxisAlignment property that takes a CrossAxisAlignment enum. This is how the children of the row will be aligned vertically.
The Row widget also has a children property that takes a list of widgets. These are the widgets that will be displayed in the row.

Column

Column(
  mainAxisAlignment: MainAxisAlignment.center,
  children: const [
    Text('Hello'),
    Text('World'),
  ],
);

The Column widget is a widget that displays its children in a vertical array.
The Column widget has a mainAxisAlignment property that takes a MainAxisAlignment enum. This is how the children of the column will be aligned.
The Column widget also has a crossAxisAlignment property that takes a CrossAxisAlignment enum. This is how the children of the column will be aligned horizontally.
The Column widget also has a children property that takes a list of widgets. These are the widgets that will be displayed in the column.

Container

Container(
  width: 100,
  height: 100,
  color: Colors.blue,
  decoration: const BoxDecoration(
    shape: BoxShape.circle,
  ),
  child: const Text('Hello World!'),
);

The Container widget is a widget that allows you to customize the size, color, and child of a widget.
The Container widget has a width property that takes a double. This is the width of the container.
The Container widget also has a height property that takes a double. This is the height of the container.
The Container widget also has a color property that takes a Color object. This is the color of the container.
The Container widget also has a child property that takes a widget. This is the widget that will be displayed inside the container.

SizedBox

SizedBox(
  width: 100,
  height: 100,
  child: const Text('Hello World!'),
);

The SizedBox widget is a widget that allows you to customize the size of a widget.
The SizedBox widget has a width property that takes a double. This is the width of the sized box.
The SizedBox widget also has a height property that takes a double. This is the height of the sized box.
The SizedBox widget also has a child property that takes a widget. This is the widget that will be displayed inside the sized box.

SingleChildScrollView

SingleChildScrollView(
  scrollDirection: Axis.horizontal,
  physics: const BouncingScrollPhysics(),
  child: Column(
    children: const [
      Text('Hello'),
      Text('World'),
    ],
  ),
);

The SingleChildScrollView widget is a widget that allows you to scroll through its children.
The SingleChildScrollView widget has a child property that takes a widget. This is the widget that will be displayed inside the scroll view.
The SingleChildScrollView widget also has a scrollDirection property that takes a Axis enum. This is the direction that the scroll view will scroll in.
The SingleChildScrollView widget also has a physics property that takes a ScrollPhysics object. This is the physics of the scroll view.

CircleAvatar

CircleAvatar(
  radius: 50,
  backgroundImage: NetworkImage(
    'https://picsum.photos/200',
  ),
);

The CircleAvatar widget is a widget that displays an image in a circle.
The CircleAvatar widget has a radius property that takes a double. This is the radius of the circle.
The CircleAvatar widget also has a backgroundImage property that takes an ImageProvider object. This is the image that will be displayed in the circle.
The CircleAvatar widget also has a child property that takes a widget. This is the widget that will be displayed inside the circle.

3. Importing Assets

Modifying the `pubspec.yaml` file

Go into the pubspec.yaml file
Under the flutter section, you'll see a assets section
Add the following code to the assets section:

  - assets/images/

This will tell Flutter to look in the assets/images/ folder for any assets that you want to use in your app
Save the pubspec.yaml file

Adding an image

create a folder called images in the assets folder
add an image to the images folder

AssetImage vs NetworkImage

There are two ways to add an image to your app
- AssetImage
  - This is used for images that are stored locally in your app
- NetworkImage
  - This is used for images that are stored on the internet

AssetImage

Image(
  image: AssetImage('assets/images/image.png'),
);

The Image widget is a widget that displays an image.
The Image widget has an image property that takes an ImageProvider object. This is the image that will be displayed.
The AssetImage widget is a widget that displays an image that is stored locally in your app.

NetworkImage

Image(
  image: NetworkImage('https://picsum.photos/200'),
);

The NetworkImage widget is a widget that displays an image that is stored on the internet.
The NetworkImage widget has a url property that takes a string. This is the url of the image that will be displayed.
The Image widget is a widget that displays an image.

Adding an image to a container

Container(
  width: 100,
  height: 100,
  decoration: BoxDecoration(
    image: DecorationImage(
      image: AssetImage('assets/images/image.png'),
    ),
  ),
);

The Container widget is a widget that allows you to customize the size, color, and child of a widget.
The Container widget has a decoration property that takes a BoxDecoration object. This is the decoration of the container.
The BoxDecoration widget is a widget that allows you to customize the decoration of a container.
The BoxDecoration widget has an image property that takes a DecorationImage object. This is the image that will be displayed in the container.

4. Creating a custom widget (example: detailsRow)

Go into the lib folder and create a folder called widgets
Create a file called details_row.dart in the widgets folder

import 'package:flutter/material.dart';

class DetailsRow extends StatelessWidget {
  const DetailsRow({
    super.key,
    required this.text,
    required this.icon,
  });

  final String text;
  final Icon icon;

  @override
  Widget build(BuildContext context) {
    return Row(
      mainAxisAlignment: MainAxisAlignment.spaceAround,
      children: [
        icon,
        Text(
          text,
          style: const TextStyle(
            color: Colors.black,
            fontSize: 20,
            fontWeight: FontWeight.bold,
          ),
        ),
        const SizedBox(),
      ],
    );
  }
}

The DetailsRow widget is a widget that displays a row of details.
We have created a custom widget called DetailsRow that takes two properties: text and icon.
The text property is a string that will be displayed in the row.
The icon property is an icon that will be displayed in the row.

Using the custom widget

Go into the main.dart file
Import the DetailsRow widget

import 'widgets/details_row.dart';

Use the DetailsRow widget

DetailsRow(
  text: 'Feels Like 70°',
  icon: const Icon(
    Icons.thermostat_outlined,
    color: Colors.black,
  ),
),

5. Creating a screen

Go into the lib folder and create a folder called screens
Create a file called home_screen.dart in the screens folder

import 'package:flutter/material.dart';

class HomeScreen extends StatelessWidget {
  const HomeScreen({
    super.key,
  });

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Weather App'),
      ),
      body: const Center(
        child: Text('Hello World!'),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {},
        child: const Icon(Icons.add),
      ),
    );
  }
}

The HomeScreen page is a widget that displays the home screen of the app.
We have created a custom page called HomeScreen.
The HomeScreen page is a stateless widget. Stateless widgets are immutable, meaning that their properties can't change—all values are final. This widget does not have to be called HomeScreen, but it is good practice to name your widget the same as your file.

Using the screen

Go into the main.dart file
Import the HomeScreen page

import 'screens/home_screen.dart';

Use the HomeScreen page

MaterialApp(
  title: 'Weather App',
  theme: ThemeData(
    primarySwatch: Colors.blue,
  ),
  home: const HomeScreen(),
  debugShowCheckedModeBanner: false,
);

Task: Creating a Single Page Weather App

Your job is to create a single page weather app that displays the current weather conditions for a given location. This will only be front-end development, so you will not need to worry about fetching data from an API.

The design of the app is up to you, and you can use any resources you want to help you with the design. You can use the Flutter Gallery as a reference.

However, The structure of the app should follow the requirements below.

Requirements

The app should have a screens folder containing any screen created in a separate file
The app should have a widgets folder containing any custom widgets created in a separate file

Optional Requirements

The app should have a models folder containing any models created in a separate file (Example, WeatherStatusModel)
Create a simple layout for the app that includes a text field for entering a location and a button to submit the location.
Display the current weather conditions for the location in a card or container.

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