c# - 查找未声明的命名空间前缀

Question

我想在加载时使用 Xml 文件检索每个未声明的命名空间前缀(其中 msCurrentContent 是内存流):

xmlCurrentDoc = new XmlDocument();
xmlCurrentDoc.Load(msCurrentContent);

例如，加载带有以下声明的 Xml 文件时: <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="mondoc" xls:schemaLocation="mondoc.xsd">

它必须检索未声明的前缀 xls不抛出异常(因为它确实知道)。

执行此操作的最佳方法是什么？

感谢您的帮助!

Answer 1

这真的很 hacky，但你可以子类化 XmlNamespaceManager并在遇到未知前缀时添加假命名空间:

public class MyXmlNamespaceManager : XmlNamespaceManager
{
    const string DefaultMissingNamespacePrefix = "http://missing.namespace.prefix.net/2014/";

    private string MissingNamespacePrefix { get; set; }
    private int NextMissingNamespaceIndex { get; set; }

    // The dictionary consists of a collection of namespace names keyed by prefix.
    public Dictionary<string, List<string>> MissingNamespaces { get; private set; }

    public MyXmlNamespaceManager(XmlNameTable nameTable)
        : this(nameTable, null) { }

    public MyXmlNamespaceManager(XmlNameTable nameTable, string missingNamespacePrefix)
        : base(nameTable)
    {
        this.MissingNamespacePrefix = (string.IsNullOrEmpty(missingNamespacePrefix) ? DefaultMissingNamespacePrefix : missingNamespacePrefix);
        this.MissingNamespaces = new Dictionary<string, List<string>>();
    }

    void AddMissingNamespace(string prefix)
    {
        if (string.IsNullOrEmpty(prefix))
            return;

        string uri;
        do
        {
            int index = NextMissingNamespaceIndex++;
            uri = MissingNamespacePrefix + index.ToString();
        }
        while (LookupPrefix(uri) != null); // Just in case.

        Debug.WriteLine(string.Format("Missing namespace \"{0}\" found, added fake namespace \"{1}\"", prefix, uri));
        AddNamespace(prefix, uri);
        MissingNamespaces.Add(prefix, uri);
    }

    public override bool HasNamespace(string prefix)
    {
        var result = base.HasNamespace(prefix);
        if (!result)
            AddMissingNamespace(prefix);
        result = base.HasNamespace(prefix);
        return result;
    }

    public override string LookupNamespace(string prefix)
    {
        var result = base.LookupNamespace(prefix);
        if (result == null)
            AddMissingNamespace(prefix);
        result = base.LookupNamespace(prefix);
        return result;
    }
}

public static class DictionaryExtensions
{
    public static void Add<TKey, TValue>(this IDictionary<TKey, List<TValue>> listDictionary, TKey key, TValue value)
    {
        if (listDictionary == null)
            throw new ArgumentNullException();
        List<TValue> values;
        if (!listDictionary.TryGetValue(key, out values))
        {
            listDictionary[key] = values = new List<TValue>();
        }
        values.Add(value);
    }
}

然后，进行测试:

        string xml = @"<?xml version=""1.0"" encoding=""UTF-8"" standalone=""no""?>
<Document xmlns:xsi=""http://www.w3.org/2001/XMLSchema-instance"" xmlns=""mondoc"" xls:schemaLocation=""mondoc.xsd"">
</Document>
";
        XmlDocument xmlDoc;

        using (var stream = new StringReader(xml))
        {
            var settings = new XmlReaderSettings();
            settings.NameTable = new NameTable();
            var manager = new MyXmlNamespaceManager(settings.NameTable);
            XmlParserContext context = new XmlParserContext(null, manager, null, XmlSpace.Default);
            using (var xmlReader = XmlReader.Create(stream, settings, context))
            {
                xmlDoc = new XmlDocument();
                xmlDoc.Load(xmlReader);
            }
        }

        string newXml;
        using (var writer = new StringWriter())
        {
            xmlDoc.Save(writer);
            newXml = writer.ToString();
        }

        Debug.WriteLine(newXml);

产生以下结果:

<?xml version="1.0" encoding="utf-16" standalone="no"?>
<Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="mondoc" xls:schemaLocation="mondoc.xsd" xmlns:xls="http://missing.namespace.prefix.net/2014/0">
</Document>

至少，这不是一个异常(exception)。注意 - 仅部分测试。