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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.

Logger.root.level = Level.ALL; // defaults to Level.INFO
Logger.root.onRecord.listen((record) {
  print('${}: ${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.

final log = Logger('MyClassName');

Here is an example of logging a debug message and an error:

var future = doSomethingAsync().then((result) {
  log.fine('Got the result: $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:

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.config(logged_content);
  • log.fine(logged_content);
  • log.finer(logged_content);
  • log.finest(logged_content);