我的用例是在出现错误时显示一个 snackbar ,但我无法捕获 SocketException,因为我没有调用 load : flutter 是。
更新(示例堆栈跟踪):
I/flutter (11702): ══╡ EXCEPTION CAUGHT BY SERVICES ╞══════════════════════════════════════════════════════════════════
I/flutter (11702): The following SocketException was thrown resolving a single-frame image stream:
I/flutter (11702): Connection failed (OS Error: Network is unreachable, errno = 101), address = (( snip )), port
I/flutter (11702): = 443
I/flutter (11702): When the exception was thrown, this was the stack:
I/flutter (11702): #0 IOClient.send (package:http/src/io_client.dart:30:23)
I/flutter (11702): <asynchronous suspension>
I/flutter (11702): #1 BaseClient._sendUnstreamed (package:http/src/base_client.dart:171:38)
I/flutter (11702): <asynchronous suspension>
I/flutter (11702): #2 BaseClient.get (package:http/src/base_client.dart:34:5)
I/flutter (11702): #3 NetworkImage._loadAsync (package:flutter/src/services/image_provider.dart:431:54)
I/flutter (11702): <asynchronous suspension>
I/flutter (11702): #4 NetworkImage.load (package:flutter/src/services/image_provider.dart:417:7)
I/flutter (11702): #5 ImageProvider.resolve.<anonymous closure>.<anonymous closure> (package:flutter/src/services/image_provider.dart:253:61)
最佳答案
我相对确定使用 NetworkImage 是不可能的,这是因为据我所知,只有在等待引发异常的结果时才能捕获异常。
幸运的是,通过一点 F12 操作,代码看起来非常简单。所以我的解决方案是将 NetworkImage 的 _loadAsync 功能复制到我自己的类中,只需几个小 tweeks。 (就像 rturning Uint8List 而不是编解码器)
utils/network_image_loader.dart
import 'package:flutter/services.dart';
import 'package:http/http.dart' as http;
import 'dart:async';
import 'dart:typed_data';
class NetworkImageLoader {
String url;
Map<String, String> headers;
NetworkImageLoader(this.url, {this.headers});
static final http.Client _httpClient = createHttpClient();
Future<Uint8List> load() async {
final Uri resolved = Uri.base.resolve(this.url);
final http.Response response = await _httpClient.get(resolved, headers: headers);
if (response == null || response.statusCode != 200)
throw new Exception('HTTP request failed, statusCode: ${response?.statusCode}, $resolved');
final Uint8List bytes = response.bodyBytes;
if (bytes.lengthInBytes == 0)
throw new Exception('NetworkImage is an empty file: $resolved');
return bytes;
}
}
一种简单的使用方法是(我使用它的方式不同,因为我正在加载图像循环并显示默认值,所以我没有测试过这种方式,但它应该可以工作,或者接近):
Widget img = new Text("Loading");
...
//Some function, ex constructor, init state, or a callback after you've done an http call
loadImage('http://imawesome.com');
...
@override
build(BuildContext context) {
return img;
}
Future<Uint8List> loadImage(String url) async {
try {
var netImg = new NetworkImageLoader(url);
var res = await netImg.load();
setState(() {
img = new Image(image: new MemoryImage(data),
height: 100.0,
width: 100.0,
fit: BoxFit.contain,
);
});
}
on Exception {
setState(() {
img = new Text("Load Failed");
}
}
}
所以,如果你想做以下任何事情,我的课很好:
编辑:
您可能还想研究图像的淡入淡出,它允许指定占位符,并且对于许多情况来说可能就足够了:https://flutter.io/cookbook/images/fading-in-images/
https://stackoverflow.com/questions/45645062/