Flutter インターネットから画像を取得できない

NetworkImageでインターネットから画像を表示したいが、画像が表示されずエラーになってしまう。

The following SocketException was thrown resolving an image codec:
Failed host lookup: 'pbs.twimg.com' (OS Error: No address associated with hostname, errno = 7)

When the exception was thrown, this was the stack

// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:async';
import 'dart:io';
import 'dart:ui' as ui;

import 'package:flutter/foundation.dart';

import 'binding.dart';
import 'debug.dart';
import 'image_provider.dart' as image_provider;
import 'image_stream.dart';

/// The dart:io implementation of [image_provider.NetworkImage].
@immutable
class NetworkImage extends image_provider.ImageProvider<image_provider.NetworkImage> implements image_provider.NetworkImage {
  /// Creates an object that fetches the image at the given URL.
  ///
  /// The arguments [url] and [scale] must not be null.
  const NetworkImage(this.url, { this.scale = 1.0, this.headers })
    : assert(url != null),
      assert(scale != null);

  @override
  final String url;

  @override
  final double scale;

  @override
  final Map<String, String>? headers;

  @override
  Future<NetworkImage> obtainKey(image_provider.ImageConfiguration configuration) {
    return SynchronousFuture<NetworkImage>(this);
  }

  @override
  ImageStreamCompleter load(image_provider.NetworkImage key, image_provider.DecoderCallback decode) {
    // Ownership of this controller is handed off to [_loadAsync]; it is that
    // method's responsibility to close the controller's stream when the image
    // has been loaded or an error is thrown.
    final StreamController<ImageChunkEvent> chunkEvents = StreamController<ImageChunkEvent>();

    return MultiFrameImageStreamCompleter(
      codec: _loadAsync(key as NetworkImage, chunkEvents, null, decode),
      chunkEvents: chunkEvents.stream,
      scale: key.scale,
      debugLabel: key.url,
      informationCollector: () => <DiagnosticsNode>[
        DiagnosticsProperty<image_provider.ImageProvider>('Image provider', this),
        DiagnosticsProperty<image_provider.NetworkImage>('Image key', key),
      ],
    );
  }

  @override
  ImageStreamCompleter loadBuffer(image_provider.NetworkImage key, image_provider.DecoderBufferCallback decode) {
    // Ownership of this controller is handed off to [_loadAsync]; it is that
    // method's responsibility to close the controller's stream when the image
    // has been loaded or an error is thrown.
    final StreamController<ImageChunkEvent> chunkEvents = StreamController<ImageChunkEvent>();

    return MultiFrameImageStreamCompleter(
      codec: _loadAsync(key as NetworkImage, chunkEvents, decode, null),
      chunkEvents: chunkEvents.stream,
      scale: key.scale,
      debugLabel: key.url,
      informationCollector: () => <DiagnosticsNode>[
        DiagnosticsProperty<image_provider.ImageProvider>('Image provider', this),
        DiagnosticsProperty<image_provider.NetworkImage>('Image key', key),
      ],
    );
  }

  // Do not access this field directly; use [_httpClient] instead.
  // We set `autoUncompress` to false to ensure that we can trust the value of
  // the `Content-Length` HTTP header. We automatically uncompress the content
  // in our call to [consolidateHttpClientResponseBytes].
  static final HttpClient _sharedHttpClient = HttpClient()..autoUncompress = false;

  static HttpClient get _httpClient {
    HttpClient client = _sharedHttpClient;
    assert(() {
      if (debugNetworkImageHttpClientProvider != null) {
        client = debugNetworkImageHttpClientProvider!();
      }
      return true;
    }());
    return client;
  }

  Future<ui.Codec> _loadAsync(
    NetworkImage key,
    StreamController<ImageChunkEvent> chunkEvents,
    image_provider.DecoderBufferCallback? decode,
    image_provider.DecoderCallback? decodeDepreacted,
  ) async {
    try {
      assert(key == this);

      final Uri resolved = Uri.base.resolve(key.url);

      final HttpClientRequest request = await _httpClient.getUrl(resolved);

      headers?.forEach((String name, String value) {
        request.headers.add(name, value);
      });
      final HttpClientResponse response = await request.close();
      if (response.statusCode != HttpStatus.ok) {
        // The network may be only temporarily unavailable, or the file will be
        // added on the server later. Avoid having future calls to resolve
        // fail to check the network again.
        await response.drain<List<int>>(<int>[]);
        throw image_provider.NetworkImageLoadException(statusCode: response.statusCode, uri: resolved);
      }

      final Uint8List bytes = await consolidateHttpClientResponseBytes(
        response,
        onBytesReceived: (int cumulative, int? total) {
          chunkEvents.add(ImageChunkEvent(
            cumulativeBytesLoaded: cumulative,
            expectedTotalBytes: total,
          ));
        },
      );
      if (bytes.lengthInBytes == 0) {
        throw Exception('NetworkImage is an empty file: $resolved');
      }

      if (decode != null) {
        final ui.ImmutableBuffer buffer = await ui.ImmutableBuffer.fromUint8List(bytes);
        return decode(buffer);
      } else {
        assert(decodeDepreacted != null);
        return decodeDepreacted!(bytes);
      }
    } catch (e) {
      // Depending on where the exception was thrown, the image cache may not
      // have had a chance to track the key in the cache at all.
      // Schedule a microtask to give the cache a chance to add the key.
      scheduleMicrotask(() {
        PaintingBinding.instance.imageCache.evict(key);
      });
      rethrow;
    } finally {
      chunkEvents.close();
    }
  }

  @override
  bool operator ==(Object other) {
    if (other.runtimeType != runtimeType) {
      return false;
    }
    return other is NetworkImage
        && other.url == url
        && other.scale == scale;
  }

  @override
  int get hashCode => Object.hash(url, scale);

  @override
  String toString() => '${objectRuntimeType(this, 'NetworkImage')}("$url", scale: $scale)';
}

import 'package:flutter/material.dart';

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


class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: const Text(
            'こんぶ @ Flutter大学',
            style: TextStyle(
              fontWeight: FontWeight.bold,
              fontSize: 16,
            ),
          ),
        ),
        body: Padding(
          padding: const EdgeInsets.all(8.0),
          child: Row(
            crossAxisAlignment: CrossAxisAlignment.start, // 上揃えにする
            children: [
              CircleAvatar(
                backgroundImage:
                    NetworkImage('https://pixabay.com/photos/landscape-evening-onaruto-bridge-7438429/'),
              ),
              SizedBox(width: 8), // 少し隙間を開ける
              Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: [
                  Row(
                    children: [
                      Text('こんぶ @ Flutter大学'),
                      SizedBox(width: 8),
                      Text('2022/05/05'),
                    ],
                  ),
                  SizedBox(height: 4),
                  Text('最高でした。'),
               IconButton(
                   onPressed: () {},
                   icon: Icon(Icons.favorite_border),
                 ),
                ],
              ),
            ],
          ),
        ),
      ),
    );
  }
}