Dart and Flutter error handling guide | Full analysis of best practices


Original text 


In-depth exploration of error handling technology in Dart and Flutter, from compile-time errors to run-time exceptions, will teach you how to gracefully handle various unexpected situations in applications. Learn best practices to make your application rock-solid and your user experience continuously optimized!

Dart, Flutter, error handling, exceptions, try-catch, best practices, compile-time errors, run-time errors, asynchronous operations, exception capture, elegant handling





*Important: Keep error logs

Let’s talk about the most important thing first, record your mistakes first.

sentry supports privatized deployment, and the development version is free to use.


Integrated code

import 'package:flutter/widgets.dart';
import 'package:sentry_flutter/sentry_flutter.dart';

Future<void> main() async {
  await SentryFlutter.init(
    (options) {
      options.dsn = 'https://examplePublicKey@o0.ingest.sentry.io/0';
      // Set tracesSampleRate to 1.0 to capture 100% of transactions for performance monitoring.
      // We recommend adjusting this value in production.
      options.tracesSampleRate = 1.0;
    appRunner: () => runApp(MyApp()),

  // or define SENTRY_DSN via Dart environment variable (--dart-define)

Understanding errors in Dart

Before we delve into error handling strategies, let’s take a look at several types of errors you may encounter in a Dart application:

  1. Compile-time errors : These errors occur during the code compilation phase and directly prevent code execution. For example, those are syntax errors and type errors.
  2. Runtime errors : These errors appear while the program is running. For example, null pointer exceptions, divide-by-zero errors, and out-of-bounds exceptions are common runtime errors.
  3. Exceptions : Dart uses exceptions to handle runtime errors and program exceptions. Exceptions can throwbe thrown explicitly via the keyword, or implicitly via built-in functions and methods.

Error handling techniques in Dart

In the world of Dart, there are several techniques for handling errors, each with its own specific application scenarios and purposes:

try-catch block

try-catchA block is like a net that catches and handles exceptions within its scope. Looking at this example, if tryan exception is thrown in the block, it will be catch“caught” and handled by the block.

try {
   // Code that may throw an exception 
  throw Exception( 'An error occurred' );
} catch (e) {
  print('Caught exception: $e');

on child clause

Dart’s onclause allows you to catch specific types of exceptions, which is useful when handling different error scenarios. In this example, the first catchblock catches Exceptionexceptions of type , while the second catchblock catches exceptions of other types.

try {
   // Code that may throw an exception 
} on Exception catch (e) {
   print ( 'Exception caught: $e ' );
} catch (e) {
  print('Unknown error: $e');

finally final block

finallyThe block is like a “logistics support”, no matter what exception occurs, it will always be executed. This is useful for doing some cleanup work, such as closing files or releasing resources. Regardless of exception or not, finallythe code in the block will be executed.

try {
   // Code that may throw an exception 
} catch (e) {
   print ( 'Exception caught: $e ' );
} finally {
  print('Cleanup tasks');

throw throw keyword

Dart’s throwkeyword is used to explicitly throw exceptions. This allows developers to handle exceptions and signal errors in their code. In the following example, if amountthe parameter is less than or equal to zero, ArgumentErroran exception will be thrown.

void depositMoney(double amount) {
  if (amount <= 0) {
    throw ArgumentError('Amount must be greater than zero');
  //Deposit logic 

Error handling in Flutter

In Flutter, error handling usually involves handling asynchronous operations, such as network requests and file I/O. Flutter provides some mechanisms for efficiently handling errors in asynchronous code:

Future error handling

When dealing with Futureobjects, you can use then()the method to handle successful results and catchError()the method to handle errors.

fetchUserData().then((data) {
   // Process successful results
}).catchError((error) {
  // Handle errors 
  print ( 'Error fetching user data: $error ' );

async asynchronous/await waiting

Dart’s asyncand awaitkeywords provide a more readable way to deal with asynchronous code. You can asyncuse blocks within functions try-catchto handle errors gracefully.

Future< void > fetchData() async {
   try {
     // Asynchronous code that may throw exceptions 
    var data = await fetchDataFromServer();
     // Process data 
  } catch (e) {
     // Handle errors 
    print ( 'Error fetching data: $e ' );

stream stream error handling

When processing streams, you can use listen()methods to handle data and errors separately.

  (data) {
    // Data processing
  onError: (error) {
    // Handle errors 
    print ( 'Error in stream: $error ' );
  onDone: () {
    // stream closed

Global error handling

When an error occurs in a Flutter application, you can use FlutterError.onErrorthe method to define a global error handling function. Here is an example:

import 'package:flutter/material.dart';

void main() {
  FlutterError.onError = (FlutterErrorDetails details) {
    // Handle errors here, such as sending error logs to a remote server or displaying error messages to the user 
    print ( 'Flutter Error: ${details.exception} ' );
     print ( 'Stack trace:\n ${details.stack } ' );

  // The FlutterError.onError method should be called at the entry point of the application (such as the main function) to ensure that it is set before the application runs.

class MyApp extends StatelessWidget {
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Error Handling',
      home: MyHomePage(),

class MyHomePage extends StatelessWidget {
  Widget build(BuildContext context) {
    return Scaffold(
        title: Text('Flutter Error Handling'),
      body: Center(
        child: RaisedButton(
          child: Text('Trigger Error'),
          onPressed: () {
            //Simulate the scenario that triggers the error 
            throw Exception( 'This is a sample error.' );

Error handling suggestions

Want to ensure effective error handling in Dart and Flutter applications? Then follow these best practices:

  1. Fail early : It’s best to handle errors where they occur to prevent them from spreading through the program.
  2. Use specific exceptions : When throwing an exception, it’s best to use a specific exception type that accurately represents the error condition.
  3. Provide meaningful error messages : Error messages should help developers quickly diagnose and resolve problems.
  4. Handle errors gracefully : Try to avoid crashing your application. Give the user an informative error prompt and record detailed error information for subsequent troubleshooting.
  5. Logging : Adding appropriate logging to your application can help track the context in which errors occur and can provide useful information when troubleshooting issues.
  6. Test for error conditions : Write test cases for possible error conditions to ensure that your error handling mechanism works as expected.


In software development, error handling is a crucial part. Whether in Dart or Flutter, handling errors effectively can improve your application’s stability and user experience. By understanding the different types of errors, mastering error-handling techniques, and following best practices, you can make your application behave like a graceful dancer when faced with unexpected situations, calmly rising to the challenge. May your code always be error-free, and may your users always enjoy a smooth and flawless experience!

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