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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.

To listen for changed level notitfications use:

Logger.root.onLevelChanged.listen((level) {
  print('The new log level is $level');

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);

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