dynamiclistboxresourcehandler.cs

实现DualList列表的Web自定义控件

using System;
using System.Web;
using System.Reflection;

namespace MetaBuilders.WebControls {

	/// <summary>
	/// The DynamicListBoxResourceHandler takes care of script support for the controls in the assembly.
	/// It is not meant to be used by your code.
	/// </summary>
	public class DynamicListBoxResourceHandler : System.Web.IHttpHandler {
		
		#region IHttpHandler Members

		/// <summary>
		/// Processes the request by emitting script embedded in the assembly.
		/// </summary>
		/// <param name="context"></param>
		void IHttpHandler.ProcessRequest(System.Web.HttpContext context) {
			String scriptFile = context.Request.QueryString[resourceKey];
			context.Response.ContentType = "text/javascript";

			context.Response.Cache.SetExpires(DateTime.Now.AddMonths(1));
			context.Response.Cache.SetCacheability(HttpCacheability.Public);
			context.Response.Cache.SetValidUntilExpires(false);
			context.Response.Cache.VaryByParams[resourceKey] = true;
			context.Response.Cache.VaryByParams[assemblyIdKey] = true;

			context.Response.Write(GetScript(context.Cache, scriptFile));
		}

		bool IHttpHandler.IsReusable {
			get {
				return true;
			}
		}

		private static readonly String handlerName = "MetaBuilders_WebControls_DynamicListBoxResourceHandler.axd";
		private static readonly String resourceKey = "r";
		private static readonly String assemblyIdKey = "c";

		#endregion

		#region Script
		internal static void RegisterScript( System.Web.UI.Page page, String scriptKey, String scriptFile ) {
			if ( !page.IsClientScriptBlockRegistered(scriptKey) ) {
				String script = "";
				if ( IsRegistered ) {
					script = "<script language='javascript' type='text/javascript' src='" + page.ResolveUrl("~/" + GetScriptUrl(scriptFile) ) + "'></script>";
				} else {
					script = "<script language='javascript' type='text/javascript'>\r\n<!--\r\n" + GetScript(page.Cache, scriptFile) + "\r\n// -->\r\n</script>";
				}
				page.RegisterClientScriptBlock(scriptKey,script);
			}
		}

		private static String GetScriptUrl(String scriptFile) {
			Assembly a = typeof( DynamicListBoxResourceHandler).Assembly;
			String assemblyId = System.IO.File.GetCreationTime( a.Location ).GetHashCode().ToString();
			return handlerName + "?" + assemblyIdKey + "=" + assemblyId + "&" + resourceKey + "=" + scriptFile;
		}

		private static String GetScript(System.Web.Caching.Cache cache, String scriptFile) {
			if ( cache == null ) {
				return GetScriptDirect(scriptFile);
			}

			String key = "MetaBuilders WebControls DynamicListBox Script " + scriptFile;
			if ( cache[key] == null ) {
				cache.Insert(key,GetScriptDirect(scriptFile));
			}
			return (String)cache[key];
		}

		private static String GetScriptDirect(String scriptFile) {
			if ( scriptFile == "DualList.js" || scriptFile == "DynamicListBox.js" ) {
				using (System.IO.StreamReader reader = new System.IO.StreamReader(typeof(DynamicListBoxResourceHandler).Assembly.GetManifestResourceStream(typeof(DynamicListBoxResourceHandler), scriptFile))) { 
					return reader.ReadToEnd();
				}
			}
			return "";
		}
		#endregion

		#region Registration
		private static Boolean IsRegistered {
			get {
				HttpContext context = HttpContext.Current;
				if ( context == null ) {
					return DetermineIsRegistered();
				}
				String cacheKey = "IHttpHandlerFactory Installed " + handlerName;
				if ( context.Cache[cacheKey] == null ) {
					context.Cache.Insert(cacheKey, DetermineIsRegistered());
				}
				return (Boolean)context.Cache[cacheKey];
			}
		}

		private static Boolean DetermineIsRegistered() {
			Object handlerMap = System.Web.HttpContext.GetAppConfig("system.web/httpHandlers");
			if ( handlerMap == null ) {
				return false;
			}

			MethodInfo findMapping = handlerMap.GetType().GetMethod("FindMapping", BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic );
			if ( findMapping == null ) {
				return false;
			}

			Object handler = findMapping.Invoke(handlerMap, new Object[] { "GET", handlerName } );
			if ( handler == null ) {
				return false;
			}

			PropertyInfo handlerPathProperty = handler.GetType().GetProperty("Path", BindingFlags.NonPublic | BindingFlags.Instance );
			if ( handlerPathProperty == null ) {
				return false;
			}

			String handlerPath = handlerPathProperty.GetValue(handler,null) as String;
			if ( handlerPath == null || handlerPath != handlerName ) {
				return false;
			}

			return true;
		}
		#endregion
	}
}