Stream errors

Learn stream errors and onError.

A stream can publish error events alongside normal elements. When an error is emitted the stream normally closes; no further elements arrive.

It is caught via onError in the listener or with try/catch. The .handleError(fn) transformer catches errors and keeps the stream going.

Example: Stream.error('boom').listen(print, onError: (e) => print('error: $e'));. The error goes to onError, print is never called.

try/catch with await for

When consuming a stream with await for, a thrown error is caught by a normal try/catch. The stream closes, the loop ends.

Example: try { await for (var x in Stream.error('boom')) print(x); } catch (e) { print('error: $e'); }. The error is caught, 'error: boom' prints.

This mirrors synchronous error handling; it looks the same in async flow.

Make main async. Add a block try { await Stream.error('boom').forEach(print); } catch (e) { print('hata: $e'); }.

Show example solution

void main() async {
  try {
    await Stream.error('boom').forEach(print);
  } catch (e) {
    print('hata: $e');
  }
}

Error-handler method

var t = s.____((e) => print('error'));

Show answer

var t = s.handleError((e) => print('error'));

Next lesson: asyncExpand