C# – asp.net web application with c# & vb.net both in codebehind

Website:

The Web Site project is compiled on the fly. You end up with a lot more DLL files, which can be a pain. It also gives problems when you have pages or controls in one directory that need to reference pages and controls in another directory since the other directory may not be compiled into the code yet. Another problem can be in publishing.

If Visual Studio isn't told to re-use the same names constantly, it will come up with new names for the DLL files generated by pages all the time. That can lead to having several close copies of DLL files containing the same class name, which will generate plenty of errors. The Web Site project was introduced with Visual Studio 2005, but it has turned out not to be popular.

Web Application:

The Web Application Project was created as an add-in and now exists as part of SP 1 for Visual Studio 2005. The main differences are the Web Application Project was designed to work similarly to the Web projects that shipped with Visual Studio 2003. It will compile the application into a single DLL file at build time. To update the project, it must be recompiled and the DLL file published for changes to occur.

Another nice feature of the Web Application project is it's much easier to exclude files from the project view. In the Web Site project, each file that you exclude is renamed with an excluded keyword in the filename. In the Web Application Project, the project just keeps track of which files to include/exclude from the project view without renaming them, making things much tidier.

Reference

The article ASP.NET 2.0 - Web Site vs Web Application project also gives reasons on why to use one and not the other. Here is an excerpt of it:

• You need to migrate large Visual Studio .NET 2003 applications to VS 2005? use the Web Application project.
• You want to open and edit any directory as a Web project without creating a project file? use Web Site project.
• You need to add pre-build and post-build steps during compilation? use Web Application project.
• You need to build a Web application using multiple Web projects? use the Web Application project.
• You want to generate one assembly for each page? use the Web Site project.
• You prefer dynamic compilation and working on pages without building entire site on each page view? use Web Site project.
• You prefer single-page code model to code-behind model? use Web Site project.

Web Application Projects versus Web Site Projects (MSDN) explains the differences between the web site and web application projects. Also, it discusses the configuration to be made in Visual Studio.

Well, it turns out that the option "Convert to web application" does NOT exist for "websites". The option "Convert to web application" does exist only for "web applications" !!!!

[emphasis mine]

So, here's the deal, to do the conversion, you need to:

• Add a new "Web Application" to your VS 2008 solution (File->Add->New Project->C#->Web->ASP.NET Web Application).

• Afterwards, you copy all the files in the old "website" to your newly created "web application", and override any files created in it by default

• The next step is the most ugly, you need to "manually" add the references in your "website" to the new "web application". I thought the VS 2008 PowerCommands toy would do this for me as it does copy references from other project types, but it didn't. You have to do it by yourself, manually, and you have to be cautious in this step if you have multiple versions of the same assembly (like AJAXToolkit in my case) or assemblies that have both GAC and local versions or so.

• Keep repeating the last step and trying to build the "web application". You'll keep getting errors like " '....' is unknown namespace. Are you missing an assembly reference? ". Make sure you have none of those except the ones where '....' is replaced by the IDs of the server controls you use. In other words, keep adding references and building the project until only the errors that exist because of missing .DESIGNER.CS or .DESIGNER.VB files.

• Afterwards, go to the "web application" root project node in VS 2008 solution explorer, and right click it, then you WILL find the option "Convert to web application". What this option does is actually making small changes to the "@Page" and "@Control" directives of pages and controls, and creating the required .DESIGNER.CS or .DESIGNER.VB files.

• Try building the "web application" again. If you get errors, see what references may be missing and/or go click the "Convert to web application" again. Sometimes, if there's any error other than those caused of missing DESIGNER files, not all the pages/controls will have those DESIGNER files created for them. Fixing the non DESIGNER problem and clicking "Convert to web application" again should do the job for this.

• Once you are done successful VS build, you should be ready to go. Start testing your web application. Optionally, you can right click the "web application" root project node in VS 2008 Solution Explorer and click "Properties" then go to the tab "Web" to set the "web application" to a virtual folder in IIS (you can create new virtual directory from there in VS). If you want to use the IIS virtual directory that the old "website" used, you need to remove that from IIS first.

• Update: When testing your pages, pay MOST ATTENTION to classes in "App_Code" folder, especially those with NO NAMESPACE. Those can be a big trap. We had a problem with two extension method overloads in the same static class that had no namespace,one extends DateTime? (Nullable) and calls another overload that extends DateTime itself. Calling the other overload as extension method passed VS 2008 compilation and gave us a compilation error ONLY IN RUNTIME (With IIS). Changing the call to the other overload from calling it as extension method to calling it as normal static method (only changing the call in the same class, calls from other classes remained extension method calls) did solve this one, but clearly, it's not as safe as it used to be in VS 2005. Especially with classes with no namespaces.

• Update2: During the conversion, VS 2008 renames your "App_Code" to "Old_App_Code". This new name sounds ugly, but DO NOT RENAME IT BACK. In the "web application" model, all code will be in one assembly. In runtime, the web server does not know what web project type you are using. It does take all code in "App_Code" folder and create a new assembly for it. This way, if you have code in folder named "App_Code", you'll end up with RUNTIME compilation errors that the same types exist in two assemblies, the one created by VS, and the one created by IIS / ASP.NET Development Server. To avoid that. leave the "Old_App_Code" with the same name, or rename it to ANYTHING EXCEPT: "App_Code". Do not place any code in such "App_Code" folder and prefereably do NOT have a folder with such name in your "web application" at all.

I know this since before but forgot it now as I have not used "website" model for long :(.