Summary - Advanced streams
- Dart course
- Advanced
- Lesson 18/83
- 5 min
Combine broadcast, transformer and debounce to write an event processor.
Summary - Advanced streams
This group covered advanced stream topics: broadcast streams (many listeners), StreamTransformer (map/where/take), debounce and throttle, error handling and asyncExpand.
Core idea: transformers are lazy and chainable; data flows when a terminal (forEach/listen) is called. A broadcast stream allows many listeners.
Errors are caught via onError or try/catch; asyncExpand turns each element into a stream and concatenates them in order.
Practice Summary: uppercase with map
Make main async. Add var s = Stream.fromIterable(['a', 'b']);. Add await s.map((x) => x.toUpperCase()).forEach(print);.
Starter code
void main() {
// make async; build ['a','b'] stream; uppercase via map; print via forEach
}Sample solution
void main() async {
var s = Stream.fromIterable(['a', 'b']);
await s.map((x) => x.toUpperCase()).forEach(print);
}Expected output
A B
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which one for many listeners?
- map
- asBroadcastStream Correct answer
- take
- asyncExpand
Explanation: asBroadcastStream allows many listeners.
2 Match the concepts
| Term | Meaning |
|---|---|
asBroadcastStream |
Many listeners |
.map |
Transform |
.take |
First n |
asyncExpand |
Element → Stream |
3 Error handling
var t = s.____((e) => print('error'));var t = s.handleError((e) => print('error'));Explanation: handleError catches errors.