/// The DataProvider class contains a single method, Instance(), which returns an instance of the
/// user-specified data provider class.
///
public class DataProvider
{
public static IDataProvider Instance()
{
//use the cache because the reflection used later is expensive
Cache cache = System.Web.HttpContext.Current.Cache;
if ( cache['IDataProvider'] == null )
{
//get the assembly path and class name from web.config
String prefix = '';
NameValueCollection context =
(NameValueCollection)ConfigurationSettings.GetConfig('appSettings');
if (context == null)
{
//can not get settings
return null;
}
String assemblyPath = context[prefix +
'DataProviderAssemblyPath'];
String className = context[prefix +
'DataProviderClassName'];
// assemblyPath presented in virtual form, must convert to
physical path
assemblyPath =
HttpContext.Current.Server.MapPath(HttpContext.Current.Request.ApplicationPath + '/bin/' +
assemblyPath);
// Uuse reflection to store the constructor of the class
that implements IWebForumDataProvider
try
{
cache.Insert( 'IDataProvider', Assembly.LoadFrom(
assemblyPath).GetType( className ).GetConstructor(new Type[0]), new CacheDependency(
assemblyPath ) );
}
catch (Exception)
{
// could not locate DLL file
HttpContext.Current.Response.Write('<b>ERROR:</b>
Could not locate file: <code>' + assemblyPath + '</code> or could not locate class <code>' +
className + '</code> in file.');
HttpContext.Current.Response.End();
}
}
return (IDataProvider)(
((ConstructorInfo)cache['IDataProvider']).Invoke(null) );
}
}
