C# XmlWriter WriteStartAttribute

Question

我想将下面的标记写入XML文件中。

<StructureMetaData xsi:schemaLocation="MSD" xmlns="MSD" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
   <!-- here a following more tags -->
</StructureMetaData>

对于这些，我做以下几点

XmlWriterSettings settings = new XmlWriterSettings
{
    Indent = true,
    IndentChars = "\t"
    CheckCharacters = false,
};

XmlWriter xmlWriter = XmlWriter.Create (filename, settings);

xmlWriter.WriteStartDocument ();
xmlWriter.WriteStartAttribute ("xsi", "schemaLocation", "MSD");
xmlWriter.WriteStartAttribute ("xmlns", "MSD");
xmlWriter.WriteStartAttribute ("xmlns", "xsi", "http://www.w3.org/2001/XMLSchema-instance");

但是，在第一次调用WriteStartAttribute之后，我得到了以下例外：

“状态文档中的令牌StartAttribute将导致无效的XML文档。”

如何将这些属性写入xml标记？

Answer 1

你有几个问题：

1. 在开始编写任何属性之前，您需要先编写根元素标记<StructureMetaData first。有一个默认的名称空间xmlns="MSD"，因此您需要在该名称空间中编写它。
2. 您正在调用XmlWriter.WriteStartAttribute()，但是此方法只写入属性名称。您仍然必须在名称之后编写值，例如，使用XmlWriter.WriteString()。或者，您可以通过对XmlWriter.WriteAttributeString()的一次调用来编写名称和值。
3. 您应该通过一个xmlWriter语句关闭并释放您的using。

下面是使用WriteStartAttribute()的代码的工作版本

using (var xmlWriter = XmlWriter.Create(filename, settings))
{
    xmlWriter.WriteStartDocument();

    var rootNamespace = "MSD";

    // Write the root element in the MSD namespace
    xmlWriter.WriteStartElement("StructureMetaData", rootNamespace);

    // Write the root element's attribute names and values
    xmlWriter.WriteStartAttribute("xsi", "schemaLocation", "http://www.w3.org/2001/XMLSchema-instance");
    xmlWriter.WriteString("MSD");
    xmlWriter.WriteStartAttribute("xmlns");
    xmlWriter.WriteString(rootNamespace);
    xmlWriter.WriteStartAttribute("xmlns", "xsi", null);
    xmlWriter.WriteString("http://www.w3.org/2001/XMLSchema-instance");

    // Write the root element contents

    // Close the root element
    xmlWriter.WriteEndElement();

    // Close the document
    xmlWriter.WriteEndDocument();
}

和使用WriteAttributeString()的更简单的版本

using (var xmlWriter = XmlWriter.Create(filename, settings))
{
    xmlWriter.WriteStartDocument();

    var rootNamespace = "MSD";

    // Write the root element in the MSD namespace
    xmlWriter.WriteStartElement("StructureMetaData", rootNamespace);

    // Write the root element's attribute names and values
    xmlWriter.WriteAttributeString("xsi", "schemaLocation", "http://www.w3.org/2001/XMLSchema-instance", "MSD");
    xmlWriter.WriteAttributeString("xmlns", rootNamespace);
    xmlWriter.WriteAttributeString("xmlns", "xsi", null, "http://www.w3.org/2001/XMLSchema-instance");

    // Write the root element contents

    // Close the root element
    xmlWriter.WriteEndElement();

    // Close the document
    xmlWriter.WriteEndDocument();
}

示例.Net小提琴显示这两个选项。

Answer 2

您必须编写一个开始元素，在该元素上写入属性：

xmlWriter.WritestartElement("StructureMetaData");
xmlWriter.WriteStartAttribute(...);

Answer 3

使用xml更容易：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Xml;
using System.Xml.Linq;

namespace ConsoleApplication72
{
    class Program
    {
        static void Main(string[] args)
        {
            string root = "<StructureMetaData xsi:schemaLocation=\"MSD\" xmlns=\"MSD\" xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\"></StructureMetaData>";

            XDocument doc = XDocument.Parse(root);
            XElement metaData = doc.Root;
            XNamespace ns = metaData.GetDefaultNamespace();

            metaData.Add(new XElement(ns + "ABC", new object[] {
                new XElement(ns + "DEF", new object[] {
                    new XAttribute("rst","abc"),
                    123}),
                new XElement(ns + "GHI", new object[] {
                    new XAttribute("uvw","def"),                    
                    456}),
                new XElement(ns + "JKL", new object[] {
                    new XAttribute("xyz","ghi"),
                    789})
            }));

            doc.Save("filename");
        }
    }
}