Logger

Small, easy to use and extensible logger which prints beautiful logs.
Inspired by logger for Android.

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Resources:

• Documentation
• Pub Package
• GitHub Repository

Getting Started

Just create an instance of Logger and start logging:

var logger = Logger();

logger.d("Logger is working!");

Instead of a string message, you can also pass other objects like List, Map or Set.

Output

Documentation

Log level

You can log with different levels:

logger.t("Trace log");

logger.d("Debug log");

logger.i("Info log");

logger.w("Warning log");

logger.e("Error log", error: 'Test Error');

logger.f("What a fatal log", error: error, stackTrace: stackTrace);

To show only specific log levels, you can set:

Logger.level = Level.warning;

This hides all trace, debug and info log events.

Options

When creating a logger, you can pass some options:

var logger = Logger(
  filter: null, // Use the default LogFilter (-> only log in debug mode)
  printer: PrettyPrinter(), // Use the PrettyPrinter to format and print log
  output: null, // Use the default LogOutput (-> send everything to console)
);

If you use the PrettyPrinter, there are more options:

var logger = Logger(
  printer: PrettyPrinter(
      methodCount: 2, // Number of method calls to be displayed
      errorMethodCount: 8, // Number of method calls if stacktrace is provided
      lineLength: 120, // Width of the output
      colors: true, // Colorful log messages
      printEmojis: true, // Print an emoji for each log message
      // Should each log print contain a timestamp
      dateTimeFormat: DateTimeFormat.onlyTimeAndSinceStart,
  ),
);

Auto detecting

With the io package you can auto detect the lineLength and colors arguments. Assuming you have imported the io package with import 'dart:io' as io; you can auto detect colors with io.stdout.supportsAnsiEscapes and lineLength with io.stdout.terminalColumns.

You should probably do this unless there's a good reason you don't want to import io, for example when using this library on the web.

LogFilter

The LogFilter decides which log events should be shown and which don't.
The default implementation (DevelopmentFilter) shows all logs with level >= Logger.level while in debug mode (i.e., running dart with --enable-asserts). In release mode all logs are omitted.

You can create your own LogFilter like this:

class MyFilter extends LogFilter {
  @override
  bool shouldLog(LogEvent event) {
    return true;
  }
}

This will show all logs even in release mode. (NOT a good idea)

LogPrinter

The LogPrinter creates and formats the output, which is then sent to the LogOutput.
You can implement your own LogPrinter. This gives you maximum flexibility.

A very basic printer could look like this:

class MyPrinter extends LogPrinter {
  @override
  List<String> log(LogEvent event) {
    return [event.message];
  }
}

If you created a cool LogPrinter which might be helpful to others, feel free to open a pull request. :)

Colors

Please note that in some cases ANSI escape sequences do not work under macOS. These escape sequences are used to colorize the output. This seems to be related to a Flutter bug that affects iOS builds: flutter/flutter#64491

However, if you are using a JetBrains IDE (Android Studio, IntelliJ, etc.) you can make use of the Grep Console Plugin and the PrefixPrinter decorator to achieve colored logs for any logger:

var logger = Logger(
    printer: PrefixPrinter(PrettyPrinter(colors: false))
);

LogOutput

LogOutput sends the log lines to the desired destination.
The default implementation (ConsoleOutput) send every line to the system console.

class ConsoleOutput extends LogOutput {
  @override
  void output(OutputEvent event) {
    for (var line in event.lines) {
      print(line);
    }
  }
}

Other provided LogOutputs are:

• FileOutput/AdvancedFileOutput
• StreamOutput

Possible future LogOutputs could send to Firebase or to Logcat. Feel free to open pull requests.

Acknowledgments

This package was originally created by Simon Choi, with further development by Harm Aarts, greatly enhancing its functionality over time.