| [](https://github.com/dart-lang/logging/actions?query=workflow%3A"Dart+CI"+branch%3Amaster) |
| [](https://pub.dev/packages/logging) |
| [](https://pub.dev/packages/logging/publisher) |
| |
| ## Initializing |
| |
| By default, the logging package does not do anything useful with the log |
| messages. You must configure the logging level and add a handler for the log |
| messages. |
| |
| Here is a simple logging configuration that logs all messages via `print`. |
| |
| ```dart |
| Logger.root.level = Level.ALL; // defaults to Level.INFO |
| Logger.root.onRecord.listen((record) { |
| print('${record.level.name}: ${record.time}: ${record.message}'); |
| }); |
| ``` |
| |
| First, set the root `Level`. All messages at or above the current level are sent to the |
| `onRecord` stream. Available levels are: |
| |
| + `Level.OFF` |
| + `Level.SHOUT` |
| + `Level.SEVERE` |
| + `Level.WARNING` |
| + `Level.INFO` |
| + `Level.CONFIG` |
| + `Level.FINE` |
| + `Level.FINER` |
| + `Level.FINEST` |
| |
| Then, listen on the `onRecord` stream for `LogRecord` events. The `LogRecord` |
| class has various properties for the message, error, logger name, and more. |
| |
| ## Logging messages |
| |
| Create a `Logger` with a unique name to easily identify the source of the log |
| messages. |
| |
| ```dart |
| final log = Logger('MyClassName'); |
| ``` |
| |
| Here is an example of logging a debug message and an error: |
| |
| ```dart |
| var future = doSomethingAsync().then((result) { |
| log.fine('Got the result: $result'); |
| processResult(result); |
| }).catchError((e, stackTrace) => log.severe('Oh noes!', e, stackTrace)); |
| ``` |
| |
| When logging more complex messages, you can pass a closure instead that will be |
| evaluated only if the message is actually logged: |
| |
| ```dart |
| log.fine(() => [1, 2, 3, 4, 5].map((e) => e * 4).join("-")); |
| ``` |
| |
| Available logging methods are: |
| |
| + `log.shout(logged_content);` |
| + `log.severe(logged_content);` |
| + `log.warning(logged_content);` |
| + `log.info(logged_content);` |
| + `log.config(logged_content);` |
| + `log.fine(logged_content);` |
| + `log.finer(logged_content);` |
| + `log.finest(logged_content);` |