Lære Error Handling | Remote Data

When working with remote data in Flutter, error handling is critical because network requests are inherently unreliable. Issues like lost connectivity, invalid responses, or server errors can disrupt the user experience or cause your app to crash if not managed properly. By implementing robust error handling, you ensure your app remains stable, users are informed of problems, and sensitive operations can be retried or gracefully degraded.

main.dart


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import 'package:flutter/material.dart';
import 'package:dio/dio.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Dio Error Handling Demo',
      home: Scaffold(
        appBar: AppBar(title: const Text('Network Error Example')),
        body: const Center(child: NetworkRequestWidget()),
      ),
    );
  }
}

class NetworkRequestWidget extends StatefulWidget {
  const NetworkRequestWidget({super.key});
  @override
  State<NetworkRequestWidget> createState() => _NetworkRequestWidgetState();
}

class _NetworkRequestWidgetState extends State<NetworkRequestWidget> {
  String _result = "Press the button to fetch data.";

  Future<void> _fetchData() async {
    final dio = Dio();
    setState(() {
      _result = "Loading...";
    });
    try {
      // Intentionally using an invalid URL to trigger an error
      final response = await dio.get('https://invalid.url.com/data');
      setState(() {
        _result = response.data.toString();
      });
    } on DioException catch (e) {
      setState(() {
        _result = "Network error: ${e.message}";
      });
    } catch (e) {
      setState(() {
        _result = "Unexpected error: $e";
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        Text(_result, textAlign: TextAlign.center),
        const SizedBox(height: 20),
        ElevatedButton(
          onPressed: _fetchData,
          child: const Text('Fetch Data'),
        ),
      ],
    );
  }
}

Providing clear user feedback is essential when network errors occur. In the previous example, the app displays an error message to inform users when a network request fails, which helps prevent confusion and frustration. For a better experience, consider adding retry strategies so users can attempt the operation again without restarting the app. This approach can be as simple as offering a Retry button, or you can implement automatic retries with exponential backoff for more advanced scenarios. The next example demonstrates a straightforward retry mechanism for failed network requests.

main.dart


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import 'package:flutter/material.dart';
import 'package:dio/dio.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Retry Network Request Demo',
      home: Scaffold(
        appBar: AppBar(title: const Text('Retry Mechanism Example')),
        body: const Center(child: RetryNetworkWidget()),
      ),
    );
  }
}

class RetryNetworkWidget extends StatefulWidget {
  const RetryNetworkWidget({super.key});
  @override
  State<RetryNetworkWidget> createState() => _RetryNetworkWidgetState();
}

class _RetryNetworkWidgetState extends State<RetryNetworkWidget> {
  String _result = "Press the button to fetch data.";
  int _retryCount = 0;
  static const int maxRetries = 3;

  Future<void> _fetchDataWithRetry() async {
    final dio = Dio();
    int attempt = 0;
    setState(() {
      _result = "Loading...";
      _retryCount = 0;
    });
    while (attempt < maxRetries) {
      try {
        // Intentionally using an invalid URL to trigger an error
        final response = await dio.get('https://invalid.url.com/data');
        setState(() {
          _result = response.data.toString();
        });
        return;
      } on DioException catch (e) {
        attempt++;
        setState(() {
          _retryCount = attempt;
        });
        if (attempt >= maxRetries) {
          setState(() {
            _result = "Failed after $attempt attempts: ${e.message}";
          });
        }
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        Text(_result, textAlign: TextAlign.center),
        if (_retryCount > 0 && _retryCount < maxRetries)
          Text("Retrying... ($_retryCount/$maxRetries)"),
        const SizedBox(height: 20),
        ElevatedButton(
          onPressed: _fetchDataWithRetry,
          child: const Text('Fetch Data with Retry'),
        ),
      ],
    );
  }
}

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main.dart


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import 'package:flutter/material.dart';
import 'package:dio/dio.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Dio Error Handling Demo',
      home: Scaffold(
        appBar: AppBar(title: const Text('Network Error Example')),
        body: const Center(child: NetworkRequestWidget()),
      ),
    );
  }
}

class NetworkRequestWidget extends StatefulWidget {
  const NetworkRequestWidget({super.key});
  @override
  State<NetworkRequestWidget> createState() => _NetworkRequestWidgetState();
}

class _NetworkRequestWidgetState extends State<NetworkRequestWidget> {
  String _result = "Press the button to fetch data.";

  Future<void> _fetchData() async {
    final dio = Dio();
    setState(() {
      _result = "Loading...";
    });
    try {
      // Intentionally using an invalid URL to trigger an error
      final response = await dio.get('https://invalid.url.com/data');
      setState(() {
        _result = response.data.toString();
      });
    } on DioException catch (e) {
      setState(() {
        _result = "Network error: ${e.message}";
      });
    } catch (e) {
      setState(() {
        _result = "Unexpected error: $e";
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        Text(_result, textAlign: TextAlign.center),
        const SizedBox(height: 20),
        ElevatedButton(
          onPressed: _fetchData,
          child: const Text('Fetch Data'),
        ),
      ],
    );
  }
}

main.dart


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import 'package:flutter/material.dart';
import 'package:dio/dio.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Retry Network Request Demo',
      home: Scaffold(
        appBar: AppBar(title: const Text('Retry Mechanism Example')),
        body: const Center(child: RetryNetworkWidget()),
      ),
    );
  }
}

class RetryNetworkWidget extends StatefulWidget {
  const RetryNetworkWidget({super.key});
  @override
  State<RetryNetworkWidget> createState() => _RetryNetworkWidgetState();
}

class _RetryNetworkWidgetState extends State<RetryNetworkWidget> {
  String _result = "Press the button to fetch data.";
  int _retryCount = 0;
  static const int maxRetries = 3;

  Future<void> _fetchDataWithRetry() async {
    final dio = Dio();
    int attempt = 0;
    setState(() {
      _result = "Loading...";
      _retryCount = 0;
    });
    while (attempt < maxRetries) {
      try {
        // Intentionally using an invalid URL to trigger an error
        final response = await dio.get('https://invalid.url.com/data');
        setState(() {
          _result = response.data.toString();
        });
        return;
      } on DioException catch (e) {
        attempt++;
        setState(() {
          _retryCount = attempt;
        });
        if (attempt >= maxRetries) {
          setState(() {
            _result = "Failed after $attempt attempts: ${e.message}";
          });
        }
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        Text(_result, textAlign: TextAlign.center),
        if (_retryCount > 0 && _retryCount < maxRetries)
          Text("Retrying... ($_retryCount/$maxRetries)"),
        const SizedBox(height: 20),
        ElevatedButton(
          onPressed: _fetchDataWithRetry,
          child: const Text('Fetch Data with Retry'),
        ),
      ],
    );
  }
}

Alt var klart?

Takk for tilbakemeldingene dine!

Seksjon 2. Kapittel 3