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() 。