How to log data to the Flutter console?

Question

I am a beginner and using IntelliJ IDEA, and I wanted to log data to the console?

I tried print() and printDebug(), but none of my data were showing in the Flutter console.

Answer 1

If you're inside a Flutter Widget, you can use debugPrint, e.g.,

import 'package:flutter/foundation.dart';

debugPrint('movieTitle: $movieTitle');

Or, use Dart's built in log() function

import 'dart:developer';

log('data: $data');

Answer 2

log() from 'dart:developer'

• It doesn't seem to have a max length limits like print() or debugPrint().

• So it comes helpful when you want to log the whole API response.

• And also helps in dart dev tools to show formatted logging.

import 'dart:developer';  //(auto import will do this even)
//example for api logging
  log("${response?.statusCode} :  ${response?.request?.path}",
          name: "Response", error: response.data);

Answer 3

The Dart print() function outputs to the system console, which you can view using flutter logs (which is basically a wrapper around adb logcat).

If you output too much at once, then Android sometimes discards some log lines. To avoid this, you can use debugPrint().

Found here: https://flutter.io/docs/testing/debugging

Answer 4

Alternatively, I have created a Logger for Flutter Apps: https://github.com/hiteshsahu/Flutter-Logger

Simply copy AppLog.dart & add to yor project and use it like this:

1. AppLog.i("Info Message"); // Simple Info message
2. AppLog.i("Home Page", tag: "User Logging"); // Info message with identifier TAG

Examples:

INPUT

    AppLog.v("-----------------------------");
    AppLog.d("I am Debug Log With Default TAG");
    AppLog.i("I am Info Log With Default TAG");
    AppLog.w("I am Warn Log With Default TAG");
    AppLog.e("I am Error Log With Default TAG");
    AppLog.wtf("I am Failure Log With Default TAG");
    AppLog.v("I am Verbose Log With Default TAG");

   //With TAGS
    AppLog.v("-----------------------------");
    AppLog.d("I am Debug Log With Custom TAG", tag: "Awesome Widget");
    AppLog.i("I am Info Log With Custom TAG", tag: "Awesome Widget");
    AppLog.w("I am Warn Log With Custom TAG", tag: "Awesome Widget");
    AppLog.e("I am Error Log With Custom TAG", tag: "Awesome Widget");
    AppLog.wtf("I am Failure Log With Custom TAG", tag: "Awesome Widget");
    AppLog.v("I am Verbose Log With Custom TAG", tag: "Awesome Widget");
    AppLog.v("-----------------------------");

OUTPUT:

Restarted application in 347ms.
FlutterApp: -----------------------------
DEBUG|FlutterApp: I am Debug Log With Default TAG
INFOⓘ|FlutterApp: I am Info Log With Default TAG
WARN⚠️|FlutterApp: I am Warn Log With Default TAG
ERROR⚠️|️FlutterApp: I am Error Log With Default TAG
WTF¯\_(ツ)_/¯|FlutterApp: I am Failure Log With Default TAG
FlutterApp: I am Verbose Log With Default TAG
FlutterApp: -----------------------------
DEBUG|Awesome Widget: I am Debug Log With Custom TAG
INFOⓘ|Awesome Widget: I am Info Log With Custom TAG
WARN⚠️|Awesome Widget: I am Warn Log With Custom TAG
ERROR⚠️|️Awesome Widget: I am Error Log With Custom TAG
WTF¯\_(ツ)_/¯|Awesome Widget: I am Failure Log With Custom TAG
Awesome Widget: I am Verbose Log With Custom TAG
FlutterApp: -----------------------------

You can also set a filter for Log Levels

AppLog.setLogLevel(log_priority); // logs below log_priority will be hidden

Where priority is always:

VERBOSE<=log_priority<= FAILURE

Priority Level: VERBOSE<DEBUG<INFO<WARNING<ERROR<FAILURE

Example Hide all info and Debug Logs:

AppLog.setLogLevel(AppLog.WARN);
AppLog.v("-----------------------------");
AppLog.d("Debug Log Will not be Visible");
AppLog.i("Info Log Will not be Visible");
AppLog.w("Warn Log Will be Visible");
AppLog.e("Error Log Will be Visible");
AppLog.wtf("Failure Log Will be Visible");
AppLog.v("Verbose Log  Will not be Visible");
AppLog.v("-----------------------------");

OUTPUT

WARN⚠️|FlutterApp: Warn Log Will be Visible
ERROR⚠️|️FlutterApp: Error Log Will be Visible
WTF¯\_(ツ)_/¯|FlutterApp: Failure Log Will be Visible

Feel free to use my logger or if you have some ideas for improvement please create PR or let me know I will improve it.

Answer 5

I replace to print command to logPrint

In Android Studio debugging Emulator.EMULATOR equal "" I will see to the logs

In production or testing I will set it to a number

const bool debugMode = (Emulator.EMULATOR=="");
void logPrint(String _s) {
    if(debugMode){
        print(_s);
    }
}
class Emulator {
    static const EMULATOR = String.fromEnvironment('EMULATOR', defaultValue: "");
}

Answer 6

I recommend the package Logger : https://pub.dev/packages/logger

This is the most used package for logging, and it clearly shows different levels of log in the console, with colors.

Answer 7

'''import 'dart:developer' as dev;'''

and then

dev.log('$var')