C#下使用XmlDocument详解

XML在开发中作为文件存储格式、数据交换的协议用的非常普遍，各个编程语言有都支持。W3C也制定了XML DOM的标准。在这里主要介绍下.Net中的XmlDocument，包括xml读取和写入等功能。

一、Xml的加载读取

1、数据等准备

Xml测试数据：

<?xml version="1.0" encoding="UTF-8"?>

-<CameraGroup WKT="UNKNOWNCS["unnamed"]">

<Camera duration="5" comment="" roll="-4.29374881997575E-14" tilt="-15.333841267255" heading="-50.5252574662688" z="770.962000000316" y="24483.2877865981" x="10533.2696556843" Picture="b22d08c9-59f2-4b21-a254-d7133eb1b7bb.jpg" Name="初始界面"/>

<Camera duration="5" comment="" roll="-9.54166404439055E-15" tilt="-12.2364039278614" heading="-71.2583141496969" z="524.34103072128" y="24767.3735196134" x="10161.8880158652" Picture="6c7e6098-6064-401c-93c0-dce573f86b5d.jpg" Name="分区1"/>

</CameraGroup>

读取的数据，我们定义了一个实体类LocationCamera，用来保存Xml解析后的数据：

public class LocationCamera

    {

        public LocationCamera()

        {

        }

        private string name;

        public string Name

        {

            get { return name; }

            set { name = value; }

        }

        private int duration;

        public int Duration

        {

            get { return duration; }

            set { duration = value; }

        }

        private double roll;//="-4.29374881997575E-14"

        public double Roll

        {

            get { return roll; }

            set { roll = value; }

        }

        private double tilt;//="-15.333841267255"

        public double Tilt

        {

            get { return tilt; }

            set { tilt = value; }

        }

        private double heading;//="-50.5252574662688"

        public double Heading

        {

            get { return heading; }

            set { heading = value; }

        }

        private double z;//="770.962000000316"

        public double Z

        {

            get { return z; }

            set { z = value; }

        }

        private double y;//="24483.2877865981"

        public double Y

        {

            get { return y; }

            set { y = value; }

        }

        private double x;//="10533.2696556843"

        public double X

        {

            get { return x; }

            set { x = value; }

        }

    }

2、Xml读取

a、Xml加载

Xml是个标准，对于用该标准存取的内容可以来自文件、内部串或者二进制流，所以对于Xml的加载有这么几种：

加载xml文件

Load(string filename); 

加载xml流

Load(Stream inStream); 

加载xml字符串

LoadXml(string xml); 

b、Xml元素读取

XmlDocument支持使用xpath表达式选择文档中节点，方法：

SelectNodes(String expression)

SelectSingleNode(string expression)

SelectNodes 返回符合expression表达式的所有元素，返回值为XmlNodeList，比如本例子是通过XmlNodeList nodelist = xmlDoc.SelectNodes("/CameraGroup/Camera");获取所有的Camera节点。

SelectSingleNode只返回第一个符合expression表达式的节点，如果没有返回null值。

返回的XmlNodeList，我们可以通过循环读取，对于单个XmlNode，我们通过Attributes获取属性值。

读取的完整代码如下：

 public static Hashtable getCameraXml(string path)

        {

            Hashtable hashtable = new Hashtable();           

            if (File.Exists(path))

            {

                XmlDocument xmlDoc = new XmlDocument();

//xml来自本地文件

                xmlDoc.Load(path);

                if (xmlDoc != null)

                {

//获取所有的Camera节点

                    XmlNodeList nodelist = xmlDoc.SelectNodes("/CameraGroup/Camera");

//遍历节点获取节点属性，并保存在LocationCamera类中

                    foreach (XmlNode node in nodelist)

                    {

                        LocationCamera locationCamera = new LocationCamera();

                        locationCamera.Name=node.Attributes["Name"].Value.ToString();

                        locationCamera.Roll=System.Convert.ToDouble(node.Attributes["roll"].Value.ToString());

                        locationCamera.Tilt = System.Convert.ToDouble(node.Attributes["tilt"].Value.ToString());

                        locationCamera.Heading = System.Convert.ToDouble(node.Attributes["heading"].Value.ToString());

                        locationCamera.X = System.Convert.ToDouble(node.Attributes["x"].Value.ToString());

                        locationCamera.Y = System.Convert.ToDouble(node.Attributes["y"].Value.ToString());

                        locationCamera.Z = System.Convert.ToDouble(node.Attributes["z"].Value.ToString());

                        hashtable.Add(locationCamera.Name, locationCamera);

                        Console.WriteLine(node.OuterXml);

                    }                   

                    return hashtable;

                }

            }

            return null;

        }

SelectNodes、SelectSingleNode也可以读取指定属性值的节点，比如XmlNodeList nodelist = xmlDoc.SelectNodes("/CameraGroup/Camera[@Name='分区1']");表示读取Name为"分区1"的所有节点。

二、Xml创建的写入

写入内容主要包括xml声明、根节点、子节点及节点属性。生成的Xml文件和代码如下：

<?xml version="1.0"?>

-<CameraGroup WKT="UNKNOWNCS["unnamed"">

<Camera X="112.42342" Name="分区1"/>

</CameraGroup>

写入的代码：

public static void writeCameraXml(string path)

        {

            XmlDocument xmlDoc = new XmlDocument();

            //创建Xml声明部分，即<?xml version="1.0" encoding="utf-8" ?>

            xmlDoc.CreateXmlDeclaration("1.0", "utf-8", "yes");

            //创建CameraGroup根节点

            XmlNode rootNode = xmlDoc.CreateElement("CameraGroup");

            //创建WKT属性

            XmlAttribute wktAttribute = xmlDoc.CreateAttribute("WKT");

            wktAttribute.Value = "UNKNOWNCS[\"unnamed\"";

            //为根节点添加属性

            rootNode.Attributes.Append(wktAttribute);

            //创建Camera子节点

            XmlNode cameraNode = xmlDoc.CreateElement("Camera");

            //创建Name属性

            XmlAttribute nameAttribute = xmlDoc.CreateAttribute("Name");

            nameAttribute.Value = "分区1";

            //为Camera添加属性

            cameraNode.Attributes.Append(nameAttribute);

            //创建X属性

            XmlAttribute xAttribute = xmlDoc.CreateAttribute("X");

            xAttribute.Value = "112.42342";

            //为Camera添加X属性

            cameraNode.Attributes.Append(xAttribute);

            //为根节点CameraGroup添加Camera子节点

            rootNode.AppendChild(cameraNode);

            //为Xml文档添加根元素

            xmlDoc.AppendChild(rootNode);

            //保存Xml文件

            xmlDoc.Save(path);//path为：@"d:\anxiuyun.xml"

        }