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这个代码有什么问题?

xmlreader .net c#

Arlen Beiler · 技术社区 · 15 年前

为什么while循环不返回任何内容?我想这和.NET有关。我有.NET 2.0。问题是,while语句将执行一次,然后退出,就像没有具有该名称的节点一样,如果确实存在的话。

下面是XML的一个示例:

<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>

代码如下:

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);
}

3 回复 | 直到 15 年前

Jon Skeet 15 年前

当您呼叫时,您已经从响应中读取了所有数据

resXML = readerStream.ReadToEnd();

…… readerStream 和 readStream 都是分层的 receiveStream 因此,一旦您通过一个读取了所有数据,就不能再通过另一个读取它。

你真的应该有一个 using 用于响应的语句——理想情况下,还包括所涉及的各种流。假设您可以创建一个 XmlReader 从一条小溪,而不仅仅是一条 StreamReader ,为什么不使用这样的东西:

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
       }
   }
}

另外,我会 通常地 建议创建 XmlDocument 或者类似的东西,而不是与 XMLRead -对于大型文档来说,它的伸缩性不如以前,但使用起来更容易。

Zenon 15 年前

为什么不使用linq-to-xml?会使代码更可读/可维护

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,乔恩所说的

Thomas 15 年前

正如jon所说,您已经读取了所有数据,所以您不能再读取它,但是,您应该能够将流的位置设置回零,然后再读取它。

接收流。位置=0;

我要说的另一个技巧是将变量“readstream”重命名为“reader”或其他东西,因为它是stream reader而不是stream。

当心, 汤姆