Flutter apps constantly handle asynchronous operations (network requests, file access, database queries). Dart's Futures (single async results) and Streams (sequences of async events), with async/await and widgets like FutureBuilder/StreamBuilder, are essential for async UI.
// a Future represents a single async result that completes later
Future<String> fetchUser() async {
final response = await http.get(url); // await pauses until the Future completes
return response.body; // returns the result
}
// using it
final data = await fetchUser(); // await the result
// or: fetchUser().then((data) => ...); // callback style
Future = a single value available later (a network response, a file read). async/await makes async code read sequentially.
// FutureBuilder rebuilds the UI based on the Future's state (loading/data/error)
FutureBuilder<String>(
future: fetchUser(),
builder: (context, snapshot) {
if (snapshot.connectionState == ConnectionState.waiting) {
return CircularProgressIndicator(); // loading
} else if (snapshot.hasError) {
return Text('Error: ${snapshot.error}'); // error
} else {
return Text(snapshot.data!); // got the data
}
},
)
// a Stream = a SEQUENCE of async events over time (e.g. live data, websocket, sensor)
Stream<int> counter() async* {
for (int i = 0; i < 10; i++) {
await Future.delayed(Duration(seconds: 1));
yield i; // emit each value
}
}
// StreamBuilder rebuilds the UI as new events arrive
StreamBuilder<int>(stream: counter(), builder: (context, snapshot) => Text('${snapshot.data}'))
Understanding async, Futures, and Streams is essential because Flutter apps constantly deal with asynchronous operations, so handling them correctly is fundamental to building real apps.
Almost every app performs async work — network requests, file access, database queries, real-time data — and Dart's async primitives are how you handle it.
Understanding Futures (representing a single async result available later, like a network response) with async/await (making async code read sequentially and cleanly) is essential for performing async operations.
Understanding FutureBuilder is particularly important for UI: it builds UI based on a Future's state, properly handling loading, error, and data states — which is exactly what real apps need (showing a spinner while loading, an error message on failure, and the data on success), a common and essential pattern for async UI.
Understanding Streams (sequences of async events over time, like live data, websockets, or sensor readings) and StreamBuilder (rebuilding the UI as new events arrive) is essential for reactive, real-time UIs and for state management approaches built on streams.
Handling async correctly — including the loading/error/data states that FutureBuilder and StreamBuilder manage — is fundamental to building apps that fetch and display data properly (the core of most apps).
Since Flutter apps constantly perform asynchronous operations (network, files, real-time data) and displaying their results requires handling async states correctly, and since Futures, Streams, async/await, and the Builder widgets are the essential tools for this, understanding async, Futures, and Streams in Flutter is essential, frequently-applied knowledge — fundamental for building apps that handle data and async operations correctly, a core skill needed in virtually every real Flutter application that fetches or processes data.