SharpDevelop 属性服务

本篇分析Core\Services的PropertyService类，该服务是用于所有需要属性持久的地方。
因为涉及到属性持久化的存储位置，所以类中存在5个静态常量，很重要：

        readonly static string propertyFileName = "SharpDevelopProperties.xml";
        readonly static string propertyFileVersion = "1.1";
        readonly static string propertyXmlRootNodeName = "SharpDevelopProperties";

        readonly static string defaultPropertyDirectory = Application.StartupPath +
                                                          Path.DirectorySeparatorChar + ".." +
                                                          Path.DirectorySeparatorChar + "data" +
                                                          Path.DirectorySeparatorChar + "options";

        readonly static string configDirectory = System.Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData) +
                                                 Path.DirectorySeparatorChar + ".ICSharpCode" +
                                                 Path.DirectorySeparatorChar + "SharpDevelop" +
                                                 Path.DirectorySeparatorChar;

持久化文件名称为SharpDevelopProperties.xml，该文件中，只读取Version=1.1以及根节点为"SharpDevelopProperties"的那一部分内容。
至于defaultPropertyDirectory 和 configDirectory ，则分别是默认属性和个性化属性，一般先在configDirectory下找，找到了直接加载或保存，找不到再去defaultPropertyDirectory目录下找。

方法很多，分为两条线：
1.在构造函数中加载属性 LoadProperties():

        void LoadProperties()
        {
            if (!Directory.Exists(configDirectory))
            {
                Directory.CreateDirectory(configDirectory);
            }

            if (!LoadPropertiesFromStream(configDirectory + propertyFileName))
            {
                Console.WriteLine("Can't read global properties in user path, using default properties");
                if (!LoadPropertiesFromStream(defaultPropertyDirectory + Path.DirectorySeparatorChar + propertyFileName))
                {
                    throw new PropertyFileLoadException();
                }
            }
        }

LoadPropertiesFromStream()方法检测文件是否存在。

2.在卸载服务UploadService时保存属性，SaveProperties():

        void SaveProperties()
        {
            WritePropertiesToFile(configDirectory + propertyFileName);
        }

        void WritePropertiesToFile(string fileName)
        {
            XmlDocument doc = new XmlDocument();
            doc.LoadXml("<?xml version=\"1.0\"?>\n<" + propertyXmlRootNodeName + " fileversion = \"" + propertyFileVersion + "\" />");

            doc.DocumentElement.AppendChild(ToXmlElement(doc));

            FileUtilityService fileUtilityService = (FileUtilityService)ServiceManager.Services.GetService(typeof(FileUtilityService));
            fileUtilityService.ObservedSave(new NamedFileOperationDelegate(doc.Save), fileName, FileErrorPolicy.ProvideAlternative);
        }

这里使用了File服务的保证例程安全的文件保存方法——ObservedSave()。