Week 2: Dart

Overview

This week, you'll learn the basics of Dart, a programming language developed by Google. Dart is used to build mobile, desktop, and web applications using the Flutter framework. You'll learn how to declare and initialize variables, handle errors, define classes, and use constructors. You'll also learn about Dart's null safety feature and build a simple task list app.

Learning Objectives

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

Install Dart on your local machine
Declare and initialize variables
Handle errors using try-catch blocks
Define classes and use constructors
Understand Dart's null safety feature
Build a simple task list app

Resources

Setup And Tutorial

1. Setup

Install Dart:
- Follow the official Flutter/Dart installation guide to download and install Dart on your local machine: https://docs.flutter.dev/get-started/install

2. Variables

Create a Dart Program:
- Create a new Dart file (e.g., variables.dart) using a text editor or code editor of your choice.

Declare and Initialize Variables:

In variables.dart, declare and initialize various types of variables (integers, strings, booleans, lists, etc.). For example:

void main() {
  int age = 30;
  String name = 'John';
  bool isStudent = true;
  List<String> fruits = ['apple', 'banana', 'cherry'];

  // Print variables
  print('Age: $age');
  print('Name: $name');
  print('Is Student: $isStudent');
  print('Fruits: $fruits');
}

Run the Program:
- Open your terminal or command prompt.
- Navigate to the folder where variables.dart is located.
- Run the Dart program using the dart command:
```
dart variables.dart
```

3. Error Handling

Modify the Dart Program:

Update variables.dart to include error handling using try-catch blocks. For example:

void main() {
  try {
    int result = 10 ~/ 0; // Division by zero to trigger an error
    print('Result: $result');
  } catch (e) {
    print('An error occurred: $e');
  }
}

Run the Modified Program:
- Run the modified Dart program as described in step 2.

4. Classes

Define the Task Class:

Create a new Dart file (e.g., task.dart) to define the Task class:

class Task {
  int id;
  String title;
  String description;
  bool isCompleted;

  Task(this.id, this.title, this.description, this.isCompleted);
}

Create Task Instances:

In variables.dart, import the task.dart file and create instances of the Task class:

import 'task.dart';

void main() {
  Task task1 = Task(1, 'Buy groceries', 'Buy milk, eggs, and bread', false);
  Task task2 = Task(2, 'Read a book', 'Read "The Catcher in the Rye"', true);

  // Print task properties
  print('Task 1: ${task1.title}, Completed: ${task1.isCompleted}');
  print('Task 2: ${task2.title}, Completed: ${task2.isCompleted}');
}

5. Constructors

Add a Constructor to Task Class:

In task.dart, add a constructor to the Task class to simplify task object creation:

class Task {
  int id;
  String title;
  String description;
  bool isCompleted;

  Task({
   required this.id,
   required this.title,
   required this.description,
   required this.isCompleted
   });
}

Or you can assign default values to the constructor parameters:

 class Task {
   int id;
   String title;
   String description;
   bool isCompleted;

   Task({
     this.id = 0,
     this.title = "",
     this.description = "",
     this.isCompleted = false,
   });
 }
 ```

Create Task Objects Using Constructors:

In variables.dart, use the new constructor to create task objects:

import 'task.dart';

void main() {
  Task task1 = Task(
   id: 1,
   title: 'Buy groceries',
   description: 'Buy milk, eggs, and bread',
   isCompleted: false,
  );
  Task task2 = Task(
   id: 2,
   title: 'Read a book',
   description: 'Read "The Catcher in the Rye"',
   isCompleted: true,
  );

  // Create a task using the constructor with default values
  Task task3 = Task()

  // Print task properties
  print('Task 1: ${task1.title}, Completed: ${task1.isCompleted}');
  print('Task 2: ${task2.title}, Completed: ${task2.isCompleted}');
  print('Task 3 (Default): ${task3.title}, Completed: ${task3.isCompleted}');
}

6. Understanding Null Safety

Enable Null Safety:
- Dart enables null safety by default. Ensure you're using Dart version 2.12 or higher.
- Annotate variables and function parameters with ? to indicate nullable types when needed. Dart's null safety will help catch null-related errors.

7. Understanding Dart IO

Read and write to console:

Use the stdin and stdout objects to read and write to the console:

import 'dart:io';

void main() {
  stdout.write('Enter your name: ');
  String? name = stdin.readLineSync();
  print('Hello, $name!');
}

Converting Console Input to other datatypes:

Use the int.parse() and double.parse() methods to convert console input to integers and doubles, respectively:

import 'dart:io';

void main() {
  stdout.write('Enter your age: ');
  int? age = int.parse(stdin.readLineSync()!);
  print('Age: $age');
}

Error Handling Console Input:

Use the tryParse() method to handle errors when converting console input to integers and doubles:

import 'dart:io';

void main() {
  stdout.write('Enter your age: ');
  int? age = int.tryParse(stdin.readLineSync()) ?? 0;
  print('Age: $age');
}

Task: Create a Task List App

Your job is to create a simple task list app using Dart. The app should allow users to add, edit, and delete tasks. The app should also allow users to mark tasks as completed. The app should be able to handle errors and display error messages to the user.

Requirements

The app should be able to add, edit, and delete tasks.
The app should be able to mark tasks as completed.
The app should be able to handle errors and display error messages to the user.

Optional Requirements

The menu should be very user-friendly and easy to use.

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