Monthly Archives: September 2007

Web Client Software Factory Knowledge Base

Check out the knowledge base page at the Web Client Guidance Community site.

You Don’t Always Need Page Modules

From my article on Page Modules some people might have gotten the wrong impression that this would be the only way to get a reference to the page given its path, but it isn't.

You can use the System.Web.UI.PageParser.GetCompiledPageInstance method to get the reference to the page before calling the System.Web.HttpServerUtility.Transfer method.

There's one caveat, though. Unlike the version of the System.Web.HttpServerUtility.Transfer method where you that takes a virtual path as an argument, this one will not change the values of the System.Web.HttpRequest.AppRelativeCurrentExecutionFilePath and System.Web.HttpRequest.CurrentExecutionFilePath properties won't change from the original request.

That can either be a problem or the solution to a problem.

ASP.NET Resource Providers and HTTP Context

Sometime ago I built a custom resource provider for ASP.NET that relied on an attribute applied to the HTTP handler (usually a page) class instead of its virtual path to determine the location of the resources. Something like this:

[ResourceLocationAttribute(ResourceLocation)]
public partial class SomePage : Page
{
  // ...
}

Since the method signature for creating a local resource provider only has an argument with the virtual path of the HTTP handler I can ignore a way this argument and use the value of the current HTTP handler:

public class MyResourceProviderFactory : System.Web.Compilation.ResourceProviderFactory
{
  // ...
  
  public override System.Web.Compilation.IResourceProvider CreateLocalResourceProvider(string virtualPath)
  {
    string location = GetLocationFromCurrentHandlerAttribute(System.Web.HttpContext.Current.CurrentHandler);
    return CreateLocalResourceProviderFromLocation(location);
  }
  
  // ...
}

Until I tried to compile my site and get a NullReferenceException. Why? Because I don't have an HTTP context when I'm compiling my site with either Visual Studio or the ASP.NET Compilation Tool (Aspnet_compiler.exe).

Well, this is just a temporary drawback. I'll just create a resource provider without the location and initialize it on its first usage with an HTTP context, since that's what will happen at run time. But I do want to be sure that, when the method to create a local resource provider is called with an HTTP context (that will be at run time), the virtual path being passed is the current execution file path. And that's easy:

public class MyResourceProviderFactory : System.Web.Compilation.ResourceProviderFactory
{
  // ...
  
  public override System.Web.Compilation.IResourceProvider CreateLocalResourceProvider(string virtualPath)
  {
    if (!virtualPath.Equals(System.Web.HttpContext.Current.Request.CurrentExecutionFilePath, StringComparison.OrdinalIgnoreCase))
    {
    	throw new ArgumentException("Invalid path.", "virtualPath");
    }
    return CreateLocalResourceProvider();
  }
  
  // ...
}

Now I'm sure that every local resource provider created at run time is for the right resource.

Until I deployed it to an IIS application. At the first request ASP.NET compiles the whole site but something is different from when I was doing it in Visual Studio: there's an HTTP context with the current execution file path being for the requested page but the local resource provider is created for every page that has a resource expression in its markup and, surprisingly, not all of them correspond to the current execution file path.

I ended up just creating a local resource provider that saves the page's virtual path and is only initialized on the first request for a resource that has a current HTTP handler and checking, then, if the saved virtual path matches the current executing file path.

public class MyResourceProviderFactory : System.Web.Compilation.ResourceProviderFactory
{
  // ...
  
  public override System.Web.Compilation.IResourceProvider CreateLocalResourceProvider(string virtualPath)
  {
    return CreateLocalResourceProvider(virtualPath);
  }
  
  // ...
}

If you want to create your own resource provider for ASP.NET, here are a few articles that can help you:

The Cost Of Client-Side Redirects In ASP.NET And Using Page Modules

I've been asked if the Page Modules are really useful and if is there such an high cost on client-side redirects.

I hope this helps to shed some light to the issue.

Introducing ASP.NET Page Modules

(Republished at http://www.codeproject.com/useritems/PageHandlerFactoryWithMod.asp)  


Introduction


This article introduces the concept of Page Modules, which are similar to HTTP Modules but related to Page Life Cycle, and the need for them.


How HTTP Modules Work


According to the documentation, using an HTTP Module, "enables you to redirect the request to an alternative page, modify the request, or perform any other request manipulation". Well, at least up until you call Server.Transfer or Server.Execute, then you loose all the ability to tap into the Page Life Cycle of the served page.


How Page Modules Work


Page Modules enables you to handle every event in the Page Life Cycle of any page as well as its creation and release.


Each Page Module has an Init method that is called when the Page Handler Factory with Modules is initialized and each Page Module can subscribe to two events: PageCreated and PageReleasing.


In the PageCreated event arguments there are properties that expose the Page being created, the Context of the HTTP request, the HTTP data transfer method (GET or POST) that the client uses, the virtual path to the requested resource and the physical application path of the requested page. Using the reference to the page being created, you can subscribe to all events in the Page Life Cycle of the page being created.


In the PageReleasing event arguments there is a property that exposes the Page being released.


Page Modules versus HTTP Modules


You can implement much of the functionality of a Page Module as an HTTP Module if you are not calling Server.Transfer or Server.Execute. However, if you are using frameworks or application blocks like the Web Client Software Factory and its Page Flow Application Block that heavily rely on client redirects, you can greatly reduce network usage and server load by using a Page Module instead of an HTTP Module, at least, for part of its work.


Implementation of the Page Handler Factory With Modules


The implementation of the PageHandlerFactoryWithModules relies solely on sub-classing the PageHandlerFactory class and exposing events corresponding to the two methods of the IHttpHandlerFactory interface (GetHandler and ReleaseHandler).


public class PageHandlerFactoryWithModules : System.Web.UI.PageHandlerFactory
{
// ...

public sealed override IHttpHandler GetHandler(HttpContext context, string requestType, string virtualPath, string path)
{
Page page = base.GetHandler(context, requestType, virtualPath, path) as Page;

if (page != null)
{
OnPageCreated(new PageCreatedEventArgs(page, context, requestType, virtualPath, path));
}

return page;
}

public sealed override void ReleaseHandler(IHttpHandler handler)
{
Page page = handler as Page;

OnPageReleasing(new PageEventArgs(page));

base.ReleaseHandler(page);
}

// ...
}


As you can see, the PageHandlerFactoryWithModules class seals the GetHandler and ReleaseHandler methods and in replacement expose the OnPageCreated and OnPageReleasing that are responsible for triggering the PageCreated and PageReleasing events.


public class PageHandlerFactoryWithModules : System.Web.UI.PageHandlerFactory
{
// ...

protected virtual void OnPageCreated(PageCreatedEventArgs pageEventArgs)
{
TriggerEvent(pageCreatedEvent, pageEventArgs);
}

protected virtual void OnPageReleasing(PageEventArgs pageEventArgs)
{
TriggerEvent(pageReleasingEvent, pageEventArgs);
}

// ...
}


At the initialization of the PageHandlerFactoryWithModules class all modules are created from the configuration information and initialized.


public class PageHandlerFactoryWithModules : System.Web.UI.PageHandlerFactory
{
// ...

public PageHandlerFactoryWithModules()
{
// ...

InitModules();
}

private void InitModules()
{
PageModulesSection section = WebConfigurationManager.GetWebApplicationSection("PauloMorgado.web/pageModules") as PageModulesSection;

this.modules = section.CreateModules();

foreach (IPageModule module in this.modules)
{
module.Init(this);
}
}

// ...
}


As you can infer from the previous code block, a Page Module is a class that implements the IPageModule interface which has only one method called Init that receives a reference to the PageHandlerFactoryWithModules instance, just like with HTTP Modules.


public interface IPageModule
{
void Init(PageHandlerFactoryWithModules context);
}

(The full implementation of the Page Module concept is in the attached code download)


How to: Create Custom Page Modules


The custom page module described in this section subscribes to the PreInit event of the page being created to change its master page.


Creating the custom page module class


To implement a custom page module all you have to do is create a class that implements the IPageMoldule interface and handle de required events.


In the current example, the module needs to subscribe to the PreInit event of the page being created and in the event handler method changes the master page if the page has one.


public class MasterModule : IPageModule
{
public MasterModule()
{
}

public void Init(PageHandlerFactoryWithModules context)
{
context.PageCreated += PageCreatedHandler;
}

private static void PageCreatedHandler(object sender, PauloMorgado.Web.UI.PageEventArgs e)
{
e.Page.PreInit += PagePreInit;
}

private static void PagePreInit(object sender, EventArgs e)
{
Page page = (sender as Page);

if (page.MasterPageFile != null)
{
page.MasterPageFile = "~/Site.master";
}
}
}


Registering the custom page module


To register the page module, you'll need to add the PauloMorgado.web configuration section group and its inner pageModules configuration section.


Then, you'll have to remove the default declaration for the *.aspx path and add the PageHandlerFactoryWithModules class as the new *.aspx handler factory.


Finally, you can add your page modules in the configuration/PauloMorgado.web/pageModules configuration section.


<?xml version="1.0"?>
<
configuration>
<
configSections>
<
sectionGroup name="PauloMorgado.web">
<
section name="pageModules" type="PauloMorgado.Web.Configuration.PageModulesSection, PauloMorgado.Web.UI.PageHandlerFactoryWithModules"/>
</
sectionGroup>
</
configSections>
<
system.web>
<httpHandlers>
<
remove verb="*" path="*.aspx"/>
<
add verb="*" path="*.aspx" validate="false" type="PauloMorgado.Web.UI.PageHandlerFactoryWithModules, PauloMorgado.Web.UI.PageHandlerFactoryWithModules"/>
</
httpHandlers>
</
system.web>
<PauloMorgado.web>
<
pageModules>
<
add name="MasterModule" type="MasterModule"/>
</
pageModules>
</
PauloMorgado.web>
</
configuration>

Testing the custom page module


In the attached code download there's a sample of the master page changing module implemented as a page module and as an HTTP module.

Visual Studio Find And Replace Regular Expression Patterns

Visual Studio comes with the a specific set of regular expressions can be used in the Find what field of the its Find and Replace Window.

Over the time I've been using Visual Studio I've come up with some tricky regular expressions that I'll be publishing in this page. Feel free to comment and contribute.

Sara Ford’s "Did you know…" Series On Visual Studio

Lately, Sara Ford has been active in her "Did you know..." series of posts on Visual Studio.