PROVIDER

ProviderEntity

  1public sealed class DataProviders
  2    {
  3        /// <summary>
  4        /// This class can not be instantiated
  5        /// </summary>
  6        private DataProviders()
  7        {
  8        }
  9
 10        private static void GetDataStoreParameters(Provider dataProvider, out string connectionString, out string databaseOwner)
 11        {
 12            databaseOwner = dataProvider.Attributes["databaseOwner"];
 13            if(databaseOwner == null || databaseOwner.Trim().Length == 0)
 14                databaseOwner = ConfigurationSettings.AppSettings[dataProvider.Attributes["databaseOwnerStringName"]];
 15
 16            connectionString = dataProvider.Attributes["connectionString"];
 17            if(connectionString == null || connectionString.Trim().Length == 0)
 18                connectionString = ConfigurationSettings.AppSettings[dataProvider.Attributes["connectionStringName"]];
 19        }
 20
 21        /// <summary>
 22        /// Creates an instance of the provider using Activator. This instance should be
 23        /// cached since it is an expesivie operation
 24        /// </summary>
 25        public static object CreateInstance(Provider dataProvider)
 26        {
 27            //Find the current attributes
 28            string connectionString = null; //dataProvider.Attributes["connectionString"];
 29            string databaseOwner = null;// dataProvider.Attributes["databaseOwner"];
 30
 31            GetDataStoreParameters(dataProvider, out connectionString, out databaseOwner);
 32
 33            //Get the type
 34            Type type  = Type.GetType(dataProvider.Type);
 35
 36            object newObject = null;
 37            if(type != null)
 38            {
 39                newObject =  Activator.CreateInstance(type,new object[]{databaseOwner,connectionString});  
 40            }
 41            
 42            if(newObject == null) //If we can not create an instance, throw an exception
 43                ProviderException(dataProvider.Name);
 44
 45            return newObject;
 46        }
 47
 48        /// <summary>
 49        /// Creates and Caches the ConstructorInfo for the specified provider. 
 50        /// </summary>
 51        public static ConstructorInfo CreateConstructorInfo (Provider dataProvider) 
 52        {
 53
 54            // The assembly should be in \bin or GAC, so we simply need
 55            // to get an instance of the type
 56            //
 57            CSConfiguration config = CSConfiguration.GetConfig();
 58            ConstructorInfo providerCnstr = null;
 59            try 
 60            {
 61                //string providerTypeName = ((Provider) config.Providers[providerName]).Type;
 62                Type type  = Type.GetType( dataProvider.Type );
 63
 64                // Insert the type into the cache
 65                //
 66                Type[] paramTypes = new Type[2];
 67                paramTypes[0] = typeof(string);
 68                paramTypes[1] = typeof(string);
 69
 70                providerCnstr = type.GetConstructor(paramTypes);
 71
 72            } 
 73            catch 
 74            {
 75                ProviderException(dataProvider.Name);
 76            }
 77
 78           if(providerCnstr == null)
 79               ProviderException(dataProvider.Name);
 80
 81            return providerCnstr;
 82        }
 83
 84        /// <summary>
 85        /// Creates an instance of the specified provider using the Cached
 86        /// ConstructorInfo from CreateConstructorInfo
 87        /// </summary>
 88        public static object Invoke(Provider dataProvider)
 89        {
 90            object[] paramArray = new object[2];
 91
 92            
 93            string dbOwner = null; 
 94            string connstring = null;
 95
 96            GetDataStoreParameters(dataProvider, out connstring, out dbOwner);
 97
 98            paramArray[0] = dbOwner;
 99            paramArray[1] = connstring;
100
101            return CreateConstructorInfo(dataProvider).Invoke(paramArray);
102        }
103
104        Exception

  通过Type.GetType()来进行类的反射，当然我们需要对其进行实例化才能调用abstract class中的方法和属性，这就要用到Activator.CreateInstance(type,new object[]{databaseOwner,connectionString}),这个方法对类进行了实例化，当然实例化这个类的构造函数中的参数为(databaseOwner,connectionString);当查找到这个构造函数进行实例化时也将DataProvider中所得到的databaseOwner,connectionString两个变量的值传递给了参数。

本文转自网魂小兵博客园博客，原文链接：http://www.cnblogs.com/xdotnet/archive/2006/10/15/provider_extend_of_cs.html，如需转载请自行联系原作者