Cart design
- Dart course
- Beginner
- Lesson 48/116
- 6 min
Design the class structure for the shopping cart.
Cart design
In this project we will build a shopping cart application step by step. The first step is to design the Cart class that will hold the products. In Dart you use a class to group related data and behavior under one roof; you will see more about classes in a later level.
A cart holds product names and prices. We use a List for this: List<String> names = []; and List<double> prices = [];. You will see more about Lists in the next section; for now know them as an empty list inside square brackets. names.length gives the count and names[i] gives the i-th element.
Fields with List
The Cart class will have two fields: names (product names) and prices (prices). In Dart class fields are defined with a direct declaration: List<String> names = [];. The <String> type parameter says the list holds String elements.
These fields are created separately for each Cart object. So var c1 = Cart(); and var c2 = Cart(); create two carts; c1.names and c2.names are two independent lists. This keeps carts from affecting each other.
Practice Define the Cart class
Define a Cart class. It has List<String> names = []; and List<double> prices = []; fields. The main part already creates a cart and prints cart ready; you only need to define the class. The output on a single line must be cart ready.
Starter code
// Define the Cart class here
void main() {
var cart = Cart();
print("cart ready");
}Sample solution
class Cart {
List<String> names = [];
List<double> prices = [];
}
void main() {
var cart = Cart();
print("cart ready");
}Expected output
cart ready
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What is a class used for in Dart?
class Cart { ... }- Build a loop
- Print to the screen
- Group data and behavior under one roof Correct answer
- Check a condition
Explanation: A class groups related data and behavior under one roof.
2 Write the List field
class Cart {
____
List<double> prices = [];
}class Cart {
List<String> names = [];
List<double> prices = [];
}Explanation: List<String> names = []; declares an empty String list.
3 Match each part to its job
| Term | Meaning |
|---|---|
class Cart |
Class declaration |
List<String> names |
Name list |
List<double> prices |
Price list |
[] |
Empty list |