logging
- Dart course
- Advanced
- Lesson 61/83
- 5 min
Learn logging with the logging package.
The logging package
logging is Dart's standard logging package. It is imported with import 'package:logging/logging.dart';. The Logger class holds log records; Level is the record level; LogRecord represents a single record.
Example: final log = Logger('uygulama'); log.info('started');. Here a logger named 'uygulama' is created and an info record is written. By default records go nowhere; you must add a handler. With Logger.root.onRecord.listen(...) you capture records and write them to the screen or a file.
Adding a handler
A Logger holds records but gives no output by default. To see records you add a handler with Logger.root.onRecord.listen(...). The handler receives a LogRecord and processes it.
Example: Logger.root.onRecord.listen((r) => print('${r.level.name}: ${r.message}'));. This handler prints each record as 'INFO: message'. r.level.name gives the level name; r.message gives the record message. You also set the minimum level with Logger.root.level = Level.INFO; records below this level are ignored.
Practice Set up a logger and log a record
Add import 'package:logging/logging.dart';. In main set the minimum level with Logger.root.level = Level.INFO;. Add a handler with Logger.root.onRecord.listen((r) => print('${r.level.name}: ${r.message}'));. Create a logger with final log = Logger('uygulama'); and log with log.info('started').
Starter code
// import the logging package
void main() {
// set root level, add handler, log a record
}Sample solution
import 'package:logging/logging.dart';
void main() {
Logger.root.level = Level.INFO;
Logger.root.onRecord.listen((r) => print('${r.level.name}: ${r.message}'));
final log = Logger('uygulama');
log.info('started');
}Expected output
INFO: started
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does the logging package do?
- Provides logging Correct answer
- Manages databases
- Makes HTTP requests
- Manipulates DOM
Explanation: the logging package provides logging.
2 Creating a Logger
final log = ____('uygulama');final log = Logger('uygulama');Explanation: Logger('uygulama') creates a logger.
3 Match the logging parts
| Term | Meaning |
|---|---|
logging |
Logging package |
Logger |
Logger |
Level |
Level |
LogRecord |
Record |