Collections

Key Points

• A collection is a data structure that allows for storing individual data objects (typically defined by individual classes) and that provides access and modification operations.
• Dart has built-in support for list, set, and map collections.
  • Lists are array-like data structures and provide an index for accessing its elements
  • Sets behave like mathematical sets and are defined by curly brackets ({}).
  • Maps are a key-value-based data structure where each item can be accessed by a unique key.
• Lists use zero-based indexing, where 0 is the index of the first value and list.length - 1 is the index of the last value.
• A typed list is the common way in Dart/Flutter for storing individual data objects (e.g. shopping cart items) in form of a collection.
• The syntactical structure is very easy: List<Type>
• Dart tries to infer the type of the items stored in lists if no type is given. This proces is called type inference.
• Store the class definitions for the individual objects in a separate model folder in the lib directory of your flutter project.
• Use the dart:collection library for more sophisticated implementations of different collection types.

Recommended Learning Resources

• Learn about the different type of collections provided per default by Dart/Flutter: https://dart.dev/language/collections
• Work through the following article to learn more about how to combine individual data classes with widgets: https://docs.flutter.dev/cookbook/lists/mixed-list
• The following page contains a list of collections provided by the dart:collection library. This list is for those groups who require more sophisticated and feature rich collections compared to the standard dart listtype: https://api.flutter.dev/flutter/dart-collection/dart-collection-library.html

How to create a list that stores different types of items

• Use an abstract class for defining the overall structure of the widget (e.g. a list item)
• The abstract class defines the methods that need to be implemented by the concrete widgets to be displayed in a list (e.g. title and subtitle of a list item)
• For each different list item type, create an individual class that implements the abstract list item class
• Store the different list items (types) in a List<ListItem> collection
• ListView.builder() constructor converts each list item (e.g. ListItem) into a widget