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Small, easy to use and extensible logger which prints beautiful logs.

Logger #

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

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Resources: #

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
      printTime: false // Should each log print contain a timestamp

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 {
  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 {
  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: https://github.com/flutter/flutter/issues/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 {
  void output(OutputEvent event) {
    for (var line in event.lines) {

Possible future LogOutputs could send to a file, 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.

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Small, easy to use and extensible logger which prints beautiful logs.

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