.NET ServiceModel.Syndication - 更改 RSS 源的编码

Question

我正在尝试解决一个错误，即我在 http://captainobvio.us 生成的所有 RSS 提要在 Internet Explorer(版本 8 和 9)中产生以下错误:

Feed code error Switch from current encoding to specified encoding not supported. Line: 1 Character: 40

<?xml version="1.0" encoding="utf-16"?>

问题是通过 HTTP header 发送的实际编码类型与文档声明的不同。以下是我将提要的输出写入 HTML 的代码:

public ContentResult Index()
        {
            var feed = _syndication.SyndicateIdeas(_repository.GetIdeas(0,15).Ideas);

            var sb = new StringBuilder();
            using (var writer = XmlWriter.Create(sb, new XmlWriterSettings { Encoding = Encoding.UTF8, NewLineHandling = NewLineHandling.Entitize, NewLineOnAttributes = true, Indent = true}))
            {
                feed.SaveAsRss20(writer);
                writer.Close();
            }

            return Content(sb.ToString(), "application/rss+xml", Encoding.UTF8);
        } 

下面是我在 .NET 4.0 中使用 System.ServiceModel.Syndication 实际构建提要的代码:

var feed = new SyndicationFeed("CaptainObvio.us - Recent Ideas",
                                          "The most recent ideas posted by the Community on CaptainObvio.us", new Uri("http://captainobvio.us/"), "CaptainObvio.us", new DateTimeOffset(ideas[0].DatePosted), items)
                           {
                               Generator = "CaptainObvio.us - http://captainobvio.us/"
                           };

            return feed;

我想做的是将 XML 文档更改为读取 utf-8 而不是 utf-16。我还检查了 Encoding 命名空间以查看是否有 UTF16 选项(这样我就可以更正 HTTP header 而不是 XML 文档)但没能找到。

是否有一种简单的方法可以直接从 System.ServiceModel.Syndication 更改 XML 文档的编码属性？解决此问题的最简单方法是什么？

Answer 1

发生这种情况的原因是因为您将 StringBuilder 传递给 XmlWriter 构造函数。 .NET 中的字符串是 unicode，因此 XmlWriter 假定为 utf-16，您无法修改它。

因此您可以使用流而不是字符串生成器，然后您可以使用设置控制编码:

var settings = new XmlWriterSettings 
{ 
    Encoding = Encoding.UTF8, 
    NewLineHandling = NewLineHandling.Entitize, 
    NewLineOnAttributes = true, 
    Indent = true 
};
using (var stream = new MemoryStream())
using (var writer = XmlWriter.Create(stream, settings))
{
    feed.SaveAsRss20(writer);
    writer.Flush();
    return File(stream.ToArray(), "application/rss+xml; charset=utf-8");
}

综上所述，一个更好、更 MVCish 和我推荐你的解决方案是编写一个 SyndicationResult:

public class SyndicationResult : ActionResult
{
    private readonly SyndicationFeed _feed;
    public SyndicationResult(SyndicationFeed feed)
    {
        if (feed == null)
        {
            throw new HttpException(401, "Not found");
        }
        _feed = feed;
    }

    public override void ExecuteResult(ControllerContext context)
    {
        var settings = new XmlWriterSettings
        {
            Encoding = Encoding.UTF8,
            NewLineHandling = NewLineHandling.Entitize,
            NewLineOnAttributes = true,
            Indent = true
        };

        var response = context.HttpContext.Response;
        response.ContentType = "application/rss+xml; charset=utf-8";
        using (var writer = XmlWriter.Create(response.OutputStream, settings))
        {
            _feed.SaveAsRss20(writer);
        }
    }
}

并且在您的 Controller 操作中只需返回此结果，这样您就不会将管道代码弄乱您的 Controller 操作:

public ActionResult Index()
{
    var ideas = _repository.GetIdeas(0, 15).Ideas;
    var feed = _syndication.SyndicateIdeas(ideas);
    return new SyndicationResult(feed);
}