Flutter cached_network_image图片缓存异常/加载失败优化

发表于 2019年12月16日
flutter

很多应用都会这么操作，把一些图像进行缓存可以提升用户体验，也能减轻资源浪费，这里以cached_network_image为例。它可以将网络图像进行本地缓存，在需要的时候直接加载，提供了两个使用方法：

CachedNetworkImage(
        imageUrl: "http://via.placeholder.com/350x150",
        placeholder: (context, url) => CircularProgressIndicator(),
        errorWidget: (context, url, error) => Icon(Icons.error),
     ),

CachedNetworkImage(

imageUrl: "http://via.placeholder.com/350x150",

placeholder: (context, url) => CircularProgressIndicator(),

errorWidget: (context, url, error) => Icon(Icons.error),

CachedNetworkImage可以直接使用，也可以通过ImageProvider使用。

Image(image: CachedNetworkImageProvider(url))

1	Image(image: CachedNetworkImageProvider(url))

如果您想同时拥有占位符功能和要在另一个窗口小部件中使用imageprovider，则可以提供imageBuilder：

CachedNetworkImage(
  imageUrl: "http://via.placeholder.com/200x150",
  imageBuilder: (context, imageProvider) => Container(
    decoration: BoxDecoration(
      image: DecorationImage(
          image: imageProvider,
          fit: BoxFit.cover,
          colorFilter:
              ColorFilter.mode(Colors.red, BlendMode.colorBurn)),
    ),
  ),
  placeholder: (context, url) => CircularProgressIndicator(),
  errorWidget: (context, url, error) => Icon(Icons.error),
),

CachedNetworkImage(

imageUrl: "http://via.placeholder.com/200x150",

imageBuilder: (context, imageProvider) => Container(

decoration: BoxDecoration(

image: DecorationImage(

image: imageProvider,

fit: BoxFit.cover,

colorFilter:

ColorFilter.mode(Colors.red, BlendMode.colorBurn)),

placeholder: (context, url) => CircularProgressIndicator(),

errorWidget: (context, url, error) => Icon(Icons.error),

图像加载失败：404，403等

如果你使用了CachedNetworkImageProvider的话，错误信息如：

I/flutter (21047): CacheManager: Failed to download file from https://pic.xx.com/28000.jpg with error:
I/flutter (21047): SocketException: Failed host lookup: 'pic.xx.com' (OS Error: No address associated with hostname, errno = 7)
I/flutter (21047): CacheManager: Failed to download file from https://pic.xx.com/23730.jpg with error:
I/flutter (21047): SocketException: Failed host lookup: 'pic.aotorun.com' (OS Error: No address associated with hostname, errno = 7)
I/flutter (21047): CacheManager: Failed to download file from  with error:
I/flutter (21047): Invalid argument(s): No host specified in URI 
I/flutter (21047): CacheManager: Failed to download file from  with error:
I/flutter (21047): Invalid argument(s): No host specified in URI 
I/flutter (21047): CacheManager: Failed to download file from https://i1.xx.com/623946/4c71965fac192ebe.jpg with error:
I/flutter (21047): HttpException: No valid statuscode. Statuscode was 404
I/flutter (21047): CacheManager: Failed to download file from https://i1.xx.com/623946/4c71965fac192ebe.jpg with error:
I/flutter (21047): HttpException: No valid statuscode. Statuscode was 404

I/flutter (21047): CacheManager: Failed to download file from https://pic.xx.com/28000.jpg with error:

I/flutter (21047): SocketException: Failed host lookup: 'pic.xx.com' (OS Error: No address associated with hostname, errno = 7)

I/flutter (21047): CacheManager: Failed to download file from https://pic.xx.com/23730.jpg with error:

I/flutter (21047): SocketException: Failed host lookup: 'pic.aotorun.com' (OS Error: No address associated with hostname, errno = 7)

I/flutter (21047): CacheManager: Failed to download file from with error:

I/flutter (21047): Invalid argument(s): No host specified in URI

I/flutter (21047): CacheManager: Failed to download file from with error:

I/flutter (21047): Invalid argument(s): No host specified in URI

I/flutter (21047): CacheManager: Failed to download file from https://i1.xx.com/623946/4c71965fac192ebe.jpg with error:

I/flutter (21047): HttpException: No valid statuscode. Statuscode was 404

I/flutter (21047): CacheManager: Failed to download file from https://i1.xx.com/623946/4c71965fac192ebe.jpg with error:

I/flutter (21047): HttpException: No valid statuscode. Statuscode was 404

如果是CachedNetworkImage则如下：

I/flutter (21047): Path:
I/flutter (21047): /data/user/0/com.example.xx/cache/libCachedImageData/68b03f20-1fa4-11ea-9f10-49083fd8fc8f.jpeg
I/flutter (21047): ════════════════════════════════════════════════════════════════════════════════════════════════════
I/flutter (21047): Another exception was thrown: Exception: Could not instantiate image codec.

I/flutter (21047): Path:

I/flutter (21047): /data/user/0/com.example.xx/cache/libCachedImageData/68b03f20-1fa4-11ea-9f10-49083fd8fc8f.jpeg

I/flutter (21047): ════════════════════════════════════════════════════════════════════════════════════════════════════

I/flutter (21047): Another exception was thrown: Exception: Could not instantiate image codec.

如何解决？

从文档提供的资料来看，没有对应的解决方案，在issues中我看到大量提出该问题的疑惑，都是在问如何解决的，但目前来看也没有相应的解决方案。其中看到最新的维护人员的回复：

I'd expect that the user of this library makes sure that the url is completely valid,
==>我希望该库的用户确保网址完全有效，

这是理想的状态，但如果图片资源涉及到第三方存储，这就难免出现意外。请求出错的情况包括但不限于：

404，图片不存在
403，无权限访问
无效图片资源，比如占位符并不是有效图像
网络不通
……

这样一看，处理起来确实麻烦，因为有时间差，即使能从返回信息来处理，但回调超时体验上就会造成体验不好。如果是能有效控制维护的数据和API当然可以像官方所说的一样，确保图片资源有效，不管是增删还是301跳转等都好处理，但这不现实。

问题还没解决，有最新进展会继续更……

解决方法一：

    precacheImage(
        CachedNetworkImageProvider(image),
        context, onError: (e, stackTrace) {
      print(('Image failed to load with error：$e'));
      setState(() {
        imgCheck = false;
      });
    });