c# - 属性上的 XElement 默认命名空间提供意外行为

Question

我在创建包含默认 namespace 和命名 namespace 的 XML 文档时遇到了问题，很难解释得更容易，只是展示我正在尝试生成的内容...

<Root xmlns="http://www.adventure-works.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:SchemaLocation="http://www.SomeLocatation.Com/MySchemaDoc.xsd">
  <Book title="Enders Game" author="Orson Scott Card" />
  <Book title="I Robot" author="Isaac Asimov" />
</Root>

但我最终得到的是这个......

<Root xmlns="http://www.adventure-works.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:SchemaLocation="http://www.SomeLocatation.Com/MySchemaDoc.xsd">
  <Book p3:title="Enders Game" p3:author="Orson Scott Card" xmlns:p3="http://www.adventure-works.com" />
  <Book p3:title="I Robot" p3:author="Isaac Asimov" xmlns:p3="http://www.adventure-works.com" />
</Root>

我为生成此 XML 片段而编写的代码是这样的...

  XNamespace aw = "http://www.adventure-works.com";
  XNamespace xsi = "http://www.w3.org/2001/XMLSchema-instance";
  XElement root = new XElement(aw + "Root",
      new XAttribute("xmlns", "http://www.adventure-works.com"),
      new XAttribute(XNamespace.Xmlns + "xsi", "http://www.w3.org/2001/XMLSchema-instance"),
      new XAttribute(xsi + "SchemaLocation", "http://www.SomeLocatation.Com/MySchemaDoc.xsd"),

      new XElement(aw + "Book",
        new XAttribute(aw + "title", "Enders Game"),
        new XAttribute(aw + "author", "Orson Scott Card")),
      new XElement(aw + "Book",
        new XAttribute(aw + "title", "I Robot"),
        new XAttribute(aw + "author", "Isaac Asimov")));

基于 example on MSDN

****编辑****

好吧，通过更多的实验，我现在对 XML namespace 的工作方式感到非常困惑....

如果我删除 aw + theattribute，我会得到我想要的……但现在看来我想要的并不是我所期望的。我以为命名空间是从它们的父级继承的，属性不也是这样吗？因为，这段读取属性的代码并没有像我预期的那样工作...

  XElement xe = XElement.Parse(textBox1.Text);
  XNamespace aw = "http://www.adventure-works.com";
  var qry = from x in xe.Descendants(aw + "Book")
            select (string)x.Attribute(aw + "author");

但是，如果我删除属性上的 aw + 就可以了，这让我假设我不能在默认命名空间中拥有属性。这是正确的吗？

Answer 1

好问题。我挖了一下，发现this bit of the XML spec :

A default namespace declaration applies to all unprefixed element names within its scope. Default namespace declarations do not apply directly to attribute names; the interpretation of unprefixed attributes is determined by the element on which they appear.

后面继续举这个例子:

For example, each of the bad empty-element tags is illegal in the following:

<!-- http://www.w3.org is bound to n1 and n2 -->
<x xmlns:n1="http://www.w3.org" 
   xmlns:n2="http://www.w3.org" >
  <bad a="1"     a="2" />
  <bad n1:a="1"  n2:a="2" />
</x>

However, each of the following is legal, the second because the default namespace does not > apply to attribute names:

<!-- http://www.w3.org is bound to n1 and is the default -->
<x xmlns:n1="http://www.w3.org" 
   xmlns="http://www.w3.org" >
  <good a="1"     b="2" />
  <good a="1"     n1:a="2" />
</x>

基本上，看起来属性名称默认情况下没有命名空间，这解释了您所看到的一切:)