What does ' yield ' keyword do in flutter?

In Flutter, the yield keyword is primarily used in the Dart language, particularly in scenarios involving asynchronous generators. It is employed to produce values for a Stream, which serves as a mechanism for implementing event-based asynchronous programming. The yield keyword enables outputting one value at a time rather than returning a complete list all at once. This approach is especially valuable for handling large datasets or processing data incrementally before it is fully ready.

Example Explanation:

Suppose we need to develop an application that retrieves large amounts of data from the network and displays each item incrementally, rather than waiting for all data to load before displaying it all at once. Here, we can use the yield keyword to implement this through Streams.

dart
// An asynchronous generator function that returns data incrementally using yield
Stream<int> fetchLargeData() async* {
  for (int i = 1; i <= 10; i++) {
    await Future.delayed(Duration(seconds: 1)); // Simulate network delay
    yield i; // Produce numbers sequentially to simulate receiving data one by one
  }
}

// Using the generated data
void displayData() async {
  await for (int value in fetchLargeData()) {
    print('Received: $value'); // Print received data sequentially
  }
}

In this example, the fetchLargeData function is an asynchronous generator marked with async*, and it uses yield to output data within the function body. This allows data generation to occur concurrently with passing it through the Stream. The displayData function processes each data item in the Stream sequentially using the await for loop. This method enables the application to handle data incrementally before it is fully ready, thereby enhancing responsiveness and efficiency.