Handling Stream Errors
When working with Streams in Dart, you need to plan for both data and error events. Streams can emit data events as well as error events, which represent exceptions or problems that occur during the stream's operation. Handling these errors is essential for building robust and reliable asynchronous code.
The onError callback allows you to respond to errors emitted by a Stream. When you listen to a Stream, you can provide separate callbacks for data, errors, and completion. The onError function receives the error object (and optionally a stack trace), letting you log, recover, or otherwise handle the problem without crashing your application.
Best practices for robust stream handling include always providing an onError callback when listening to a Stream, especially if the Stream's source can fail or is external (such as network requests or file operations). You should also consider how your application should respond to errors: sometimes you might want to simply log them, other times you may need to retry, alert the user, or clean up resources. Remember, if you do not handle errors, unhandled exceptions in Streams can terminate your program or leave it in an inconsistent state.
stream_error_handling.dart
12345678910111213141516171819202122232425void main() { // Create a Stream that emits values and then an error Stream<int> numberStream = Stream<int>.fromIterable([1, 2, 3]) .transform(StreamTransformer.fromHandlers( handleData: (data, sink) { sink.add(data); if (data == 2) { sink.addError('An error occurred at value 2'); } }, )); // Listen to the Stream, handling both data and errors numberStream.listen( (data) { print('Received: $data'); }, onError: (error) { print('Error caught: $error'); }, onDone: () { print('Stream closed.'); }, ); }
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When working with Streams in Dart, you need to plan for both data and error events. Streams can emit data events as well as error events, which represent exceptions or problems that occur during the stream's operation. Handling these errors is essential for building robust and reliable asynchronous code.
The onError callback allows you to respond to errors emitted by a Stream. When you listen to a Stream, you can provide separate callbacks for data, errors, and completion. The onError function receives the error object (and optionally a stack trace), letting you log, recover, or otherwise handle the problem without crashing your application.
Best practices for robust stream handling include always providing an onError callback when listening to a Stream, especially if the Stream's source can fail or is external (such as network requests or file operations). You should also consider how your application should respond to errors: sometimes you might want to simply log them, other times you may need to retry, alert the user, or clean up resources. Remember, if you do not handle errors, unhandled exceptions in Streams can terminate your program or leave it in an inconsistent state.
stream_error_handling.dart
12345678910111213141516171819202122232425void main() { // Create a Stream that emits values and then an error Stream<int> numberStream = Stream<int>.fromIterable([1, 2, 3]) .transform(StreamTransformer.fromHandlers( handleData: (data, sink) { sink.add(data); if (data == 2) { sink.addError('An error occurred at value 2'); } }, )); // Listen to the Stream, handling both data and errors numberStream.listen( (data) { print('Received: $data'); }, onError: (error) { print('Error caught: $error'); }, onDone: () { print('Stream closed.'); }, ); }
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