What is a Stream?
- Flutter course
- Intermediate
- Lesson 27/99
- 4 min
Learn that a Stream emits multiple values over time.
What is Stream?
Stream is a data flow that can produce multiple values over time. While a Future produces a single value, a Stream keeps emitting values.
Stream<int> numbers() async* {
yield 1;
yield 2;
yield 3;
}You produce a Stream with async* and yield.
async* and yield
To produce a Stream, you write a function marked with async*. You publish each value with yield.
Stream<int> numbers() async* {
yield 1;
yield 2;
}Each yield adds a value to the stream.
Practice Produce a number stream with async*
Write an async* function named sayiAkisi returning Stream<int>. Produce 0, 1 and 2 with yield. In main, listen to the stream and print each value with print('değer: $deger').
Starter code
import 'package:flutter/material.dart';
// sayiAkisi fonksiyonunu ekle
void main() {
final stream = sayiAkisi();
stream.listen((deger) {
print('değer: $deger');
});
}Sample solution
import 'package:flutter/material.dart';
Stream<int> sayiAkisi() async* {
yield 0;
yield 1;
yield 2;
}
void main() {
final stream = sayiAkisi();
stream.listen((deger) {
print('değer: $deger');
});
}Expected output
değer: 0 değer: 1 değer: 2
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What is the main difference between Stream and Future?
- Stream only throws errors
- Future produces one value, Stream many Correct answer
- Stream produces one value, Future many
- Neither produces any value
Explanation: Future produces a single value and completes; Stream keeps producing multiple values over time.
2 Produce a value with yield
Stream<int> sayilar() async* {
____ 1;
yield 2;
}Stream<int> sayilar() async* {
yield 1;
yield 2;
}Explanation: Inside an async* function, yield adds a value to the stream; each yield publishes one value.
3 Stream parts
| Term | Meaning |
|---|---|
Stream |
Flow producing multiple values over time |
async* |
Marker for Stream-producing function |
yield |
Adding a value to the stream |
Future |
Async result producing a single value |