Android has logcat system for application logging, and macOS/iOS also has similar logging system.

Native logger is flutter plugin to put logs to these platform native logging system.
It also shows log to console.

	Android	macOS	iOS
Support	all	11.0+	14.0+

On Android, you can see the logs using adb command.

$ adb shell 'logcat -v time --pid=$(pidof -s io.github.miyu1.simple_native_logger_example)'
10-07 17:41:51.515 V/MyApp   (27300): verbose log
10-07 17:41:53.623 D/MyApp   (27300): debug log
10-07 17:41:53.623 D/MyApp   (27300): 	additional line
10-07 17:42:07.351 I/MyApp   (27300): info log
10-07 17:42:09.065 W/MyApp   (27300): warning log
10-07 17:42:11.107 E/MyApp   (27300): error log
10-07 17:42:12.923 E/MyApp   (27300): fatal log

On macOS/iOS, you can see the logs using macOS Console app,

or by log command. (For iOS simulator, run 'xcrun simctl spawn booted log' command with same parameter.)

$ log stream  --level debug --predicate 'subsystem = "io.github.miyu1.simpleNativeLoggerExample"'
Filtering the log data using "subsystem == "io.github.miyu1.simpleNativeLoggerExample""
Timestamp                       Thread     Type        Activity             PID    TTL  
2024-10-07 17:27:14.563742+0900 0x12365d   Debug       0x0                  47876  0    simple_native_logger_example: (simple_native_logger) [io.github.miyu1.simpleNativeLoggerExample:MyApp] verbose log
2024-10-07 17:27:19.193394+0900 0x12365d   Debug       0x0                  47876  0    simple_native_logger_example: (simple_native_logger) [io.github.miyu1.simpleNativeLoggerExample:MyApp] debug log
	additional line
2024-10-07 17:27:22.057604+0900 0x12365d   Info        0x0                  47876  0    simple_native_logger_example: (simple_native_logger) [io.github.miyu1.simpleNativeLoggerExample:MyApp] info log
2024-10-07 17:27:23.590778+0900 0x12365d   Default     0x0                  47876  0    simple_native_logger_example: (simple_native_logger) [io.github.miyu1.simpleNativeLoggerExample:MyApp] warning log 
2024-10-07 17:27:24.658391+0900 0x12365d   Error       0x0                  47876  0    simple_native_logger_example: (simple_native_logger) [io.github.miyu1.simpleNativeLoggerExample:MyApp] error log
2024-10-07 17:27:26.124623+0900 0x12365d   Fault       0x213311             47876  0    simple_native_logger_example: (simple_native_logger) [io.github.miyu1.simpleNativeLoggerExample:MyApp] fatal log 

Usage

import 'package:simple_native_logger/simple_native_logger.dart';

void main() {
  SimpleNativeLogger.init();
  ...
}
  ...
  final _nativeLogger = SimpleNativeLogger(tag: "MyApp");
  _nativeLogger.w("<log message>");

  try {
    ... 
  } catch (ex, stack) {
    _nativeLogger.e(ex, stack: stack);
  }

To use simple_native_logger, you have to call SimpleNativeLogger.init() once, may be in main.
Then anywhere in code, you can use SimpleNativeLogger class for logging.
You can also pass optional stack trace parameter.

Following table lists SimpleNativeLogger methods and corresponding method on each platform.

simple_native_logger	android	iOS/macos
SimpleNativeLogger.v	Log.v	Logger.debug
SimpleNativeLogger.d	Log.d	Logger.debug
SimpleNativeLogger.i	Log.i	Logger.info
SimpleNativeLogger.w	Log.w	Logger.notice
SimpleNativeLogger.e	Log.e	Logger.error
SimpleNativeLogger.f	Log.wtf	Logger.fault

On Android, android.util.Log class is used to implement.
Tag property of SimpleNativeLogger is used as tag parameter of the Log class.
When useIsLoggable property is set to true, Log.isLoggable is also called before log.

On macOS/iOS, os.Logger class is used to implement.
Tag property of SimpleNativeLogger is used as category parameter of the Logger class.
Subsystem parameter of os.Logger is fixed to bundle ID.

Notice for Android

When useIsLoggable property is set to true, verbose and debug log is not logged, by default.
Use adb command to change behavior.
Currently android log is also shown to console, and the adb settings also affects to it.

$ adb shell
emu64xa:/ $ setprop log.tag.MyApp V
emu64xa:/ $ exit
$ flutter run
...
V/MyApp   ( 4150): verbose log (package:simple_native_logger_example/main.dart:87:33)
D/MyApp   ( 4150): debug log
D/MyApp   ( 4150): 	additional line (package:simple_native_logger_example/main.dart:93:33)
I/MyApp   ( 4150): info log (package:simple_native_logger_example/main.dart:99:33)
W/MyApp   ( 4150): warning log (package:simple_native_logger_example/main.dart:105:33)
E/MyApp   ( 4150): error log (package:simple_native_logger_example/main.dart:111:33)
E/MyApp   ( 4150): fatal log (package:simple_native_logger_example/main.dart:117:33)

MyApp is a tag I used in exmaple app. Change it to your own.
Setprop value V is for verbose level, so all log will be logged.

To reset,

$ adb shell  
emu64xa:/ $ setprop log.tag.MyApp ""
emu64xa:/ $ exit

On emulator test(Android 14), even if useIsLoggable is false, it is able to limit lower level log by adb setprop.

Notice for macOS/iOS

By default, verbose, debug and info log is not shown by console app or log command.
To change this behavior on console app, use Action menu of it.

For log command, and '--level debug' option.

Currently, macOS/iOS logs are not shown in flutter console.
So I added code to show logs to flutter console. isEchoNeeded and echo method of SimpleNativeLogger do the job.

$ flutter run
flutter: [MyApp:V] verbose log (package:simple_native_logger_example/main.dart:87:33)
flutter: [MyApp:D] debug log
flutter: 	additional line (package:simple_native_logger_example/main.dart:93:33)
flutter: [MyApp:I] info log (package:simple_native_logger_example/main.dart:99:33)
flutter: [MyApp:W] warning log (package:simple_native_logger_example/main.dart:105:33)
flutter: [MyApp:E] error log (package:simple_native_logger_example/main.dart:111:33)
flutter: [MyApp:F] fatal log (package:simple_native_logger_example/main.dart:117:33)