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"
        }

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