Recap - Data Fetcher

Let's build a DataFetcher class that brings together all the async OOP concepts from this chapter! You'll create a data service that uses async initialization, async methods for fetching individual items, and a stream for delivering multiple results over time.

You'll organize your code into two files:

• data_fetcher.dart: Create a DataFetcher class that simulates fetching data from a remote source. Your class should have:
  • A final String field called source that stores where the data comes from
  • A private constructor that initializes the source
  • A static async factory method connect(String sourceName) that returns a Future<DataFetcher>. Simulate a connection delay of 100 milliseconds, then return a new instance with the source set to the provided name
  • An async method fetchItem(int id) that returns a Future<String>. Simulate a 50 millisecond delay, then return a string in the format: [source]-Item-[id]
  • A stream generator method fetchMultiple(int count) that returns a Stream<String>. This should yield items for IDs from 1 up to and including count, using your fetchItem method for each one (await each fetch before yielding)
• main.dart: Import your data fetcher and demonstrate all three async patterns working together:
  • Print Connecting to data source...
  • Use the async factory to connect to a source named CloudDB
  • Print Connected to [source] using the fetcher's source field
  • Print an empty line
  • Print Fetching single item:
  • Fetch and print the item with ID 42
  • Print an empty line
  • Print Fetching multiple items:
  • Use await for to iterate through fetchMultiple(3) and print each item
  • Print an empty line
  • Print All operations complete!

This challenge combines the static async factory pattern for initialization, regular async methods for single operations, and async* with yield for streaming multiple results. Notice how the stream method can call other async methods internally!

Expected output:

Connecting to data source...
Connected to CloudDB

Fetching single item:
CloudDB-Item-42

Fetching multiple items:
CloudDB-Item-1
CloudDB-Item-2
CloudDB-Item-3

All operations complete!