如何将文档类型添加到XDocument？

I have an existing XDocument object that I would like to add an XML doctype to. For example:

我有一个现有的XDocument对象，我想添加一个XML文档类型。例如：

XDocument doc = XDocument.Parse("<a>test</a>");

I can create an XDocumentType using:

我可以使用以下方法创建XDocumentType：

XDocumentType doctype = new XDocumentType("a", "-//TEST//", "test.dtd", "");

But how do I apply that to the existing XDocument?

但是，我如何将其应用于现有的XDocument？

2 个解决方案

#1

You can add an XDocumentType to an existing XDocument, but it must be the first element added. The documentation surrounding this is vague.

您可以将XDocumentType添加到现有XDocument，但它必须是添加的第一个元素。围绕这个的文档含糊不清。

Thanks to Jeroen for pointing out the convenient approach of using AddFirst in the comments. This approach allows you to write the following code, which shows how to add the XDocumentType after the XDocument already has elements:

感谢Jeroen指出在评论中使用AddFirst的便捷方法。此方法允许您编写以下代码，其中显示了在XDocument已有元素之后如何添加XDocumentType：

var doc = XDocument.Parse("<a>test</a>");
var doctype = new XDocumentType("a", "-//TEST//", "test.dtd", "");
doc.AddFirst(doctype);

Alternately, you could use the Add method to add an XDocumentType to an existing XDocument, but the caveat is that no other element should exist since it has to be first.

或者，您可以使用Add方法将XDocumentType添加到现有的XDocument，但需要注意的是，不应存在其他元素，因为它必须是第一个。

XDocument xDocument = new XDocument();
XDocumentType documentType = new XDocumentType("Books", null, "Books.dtd", null);
xDocument.Add(documentType);

On the other hand, the following is invalid and would result in an InvalidOperationException: "This operation would create an incorrectly structured document."

另一方面，以下内容无效，并将导致InvalidOperationException：“此操作将创建一个不正确的结构化文档。”

xDocument.Add(new XElement("Books"));
xDocument.Add(documentType);  // invalid, element added before doctype

#2

Just pass it to the XDocument constructor (full example):

只需将它传递给XDocument构造函数（完整示例）：

XDocument doc = new XDocument(
    new XDocumentType("a", "-//TEST//", "test.dtd", ""),
    new XElement("a", "test")
);

or use XDocument.Add (the XDocumentType has to be added before the root element):

或者使用XDocument.Add（必须在根元素之前添加XDocumentType）：

XDocument doc = new XDocument();
doc.Add(new XDocumentType("a", "-//TEST//", "test.dtd", ""));
doc.Add(XElement.Parse("<a>test</a>"));

#1