Question

为什么while循环没有返回任何内容？我认为这与.NET有关。我有.NET 2.0。问题是while语句将执行一次然后退出，就好像没有具有该名称的节点，当肯定存在时。

以下是XML的示例：

<rss version="2.0">
    <channel>
        <title>...</title>
        <link>...</link>
        <description>...</description>
        <lastBuildDate>...</lastBuildDate>
        <item>
            <title>User greeting</title>
            <guid>...</guid>
            <link>http://...</link>

            <description>Voicebox number: 1</description>
            <author>Free Conference Call</author>
        </item>
        <item>
            <title>User greeting</title>
            <guid>...</guid>
            <link>http://...</link>

            <description>Voicebox number: 1</description>
            <author>Free Conference Call</author>
        </item>
    </channel>
</rss>

以下是代码：

HttpWebRequest webreq = (HttpWebRequest)WebRequest.Create (reqURL);
// Set some reasonable limits on resources used by this request
webreq.MaximumAutomaticRedirections = 4;
webreq.MaximumResponseHeadersLength = 4;
//====================
// Set credentials to use for this request.
webreq.Credentials = CredentialCache.DefaultCredentials;
HttpWebResponse response = (HttpWebResponse)webreq.GetResponse ();
//====================
// Get the stream associated with the response.
receiveStream = response.GetResponseStream ();
//====================
// Pipes the stream to a higher level stream reader with the required encoding format. 
readStream = new StreamReader(receiveStream, Encoding.UTF8);
resXML = readStream.ReadToEnd();
readStream = new StreamReader(receiveStream, Encoding.UTF8);
//====================
Console.WriteLine(resXML);
Stream XMLStream = receiveStream;
readStream = new StreamReader(XMLStream, Encoding.UTF8);

XmlReaderSettings settings = new XmlReaderSettings();
settings.ConformanceLevel = ConformanceLevel.Fragment;
settings.IgnoreWhitespace = true;
settings.IgnoreComments = true;
XmlReader reader = System.Xml.XmlReader.Create(readStream, settings);

while(reader.EOF == false)
{
    reader.ReadToFollowing("link");
    Console.WriteLine("link: " + reader.Value);
    //=======================================
    reader.ReadToFollowing("description");
    Console.WriteLine("descrip: " + reader.Value);
}

Answer 1

调用

时，您已经阅读了响应中的所有数据

resXML = readerStream.ReadToEnd();

... readerStream和readStream都位于receiveStream之上，所以一旦您通过一个读取了所有数据，就无法再通过其他

对于响应，您应该有一个using语句 - 理想情况下涉及的各种流。鉴于您可以从流中创建XmlReader，而不仅仅是StreamReader，为什么不使用这样的内容：

XmlReaderSettings settings = new XmlReaderSettings();
settings.ConformanceLevel = ConformanceLevel.Fragment;
settings.IgnoreWhitespace = true;
settings.IgnoreComments = true;

using (HttpWebResponse response = (HttpWebResponse)webreq.GetResponse())
{
   using (Stream stream = response.GetResponseStream())
   {
       using(XmlReader reader = XmlReader.Create(stream, settings))
       {
           // Do stuff here
       }
   }
}

此外，我通常建议创建一个XmlDocument或类似的东西，而不是使用XmlReader - 它不适用于大型文档，但它是更容易使用。

Answer 2

为什么不使用Linq-to-XML？将使更易读/可维护的代码

XElement rssFile = XElement.Load(content);
IEnumerable<XElement> channels = rssFile.Descendants("channel");
foreach(XElement channel in channels)
{
    Console.WriteLine("link: " + channel.Element("link").Value);
    Console.WriteLine("description: " + channel.Element("description").Value);
}

除此之外，Jon说了什么

Answer 3

像Jon说你已经阅读了所有数据，所以你不能再读它，但是，你应该能够将流的位置设置回零，然后再读一遍。

receiveStream.Position = 0;

我要说的另一个提示是将变量“readStream”重命名为“reader”或其他内容，因为它是StreamReader而不是Stream。

保重，汤姆

这段代码出了什么问题

3 个答案: