share ASP.NET user controls between applications (aspnet_merge)

You want to create some shared ASP.NET controls for use in multiple applications.
Probably the only way you think of is custom control:

the only way to share the user control between applications is to put a separate copy in each application, which takes more maintenance if you make changes to the control (MSDN)

But it isn't actually true.

You can use "Web Deployment Projects" add-in to compile your user controls project into dll which can be referenced from any web application.

Now let's take it step by step:

(make sure you have installed the "Web Deployment Projects" add-in)

1. Create a new web project (SharedUserControls.csproj).
2. Remove the "Default.aspx" page and web.config file.
3. Add a user control (let's call it MyControl.ascx).
4. Add what ever web controls you want to your user control.
   
    
5. Add Web Deployment Project by standing on the project and selecting "Add Web Project Project..." from the Build menu
   
    
6. Keep the default name, and click OK.
   
    
   A new project was created with out any file inside
   
    
7. Double click the new project to get the project property pages.
   
    
8. Uncheck the last check box - "Allow this precompiled site to be updatable".
   
   This is an important step - If you'll skip it, you'll get: ASPNETMERGE : warning 1013: Cannot find any assemblies that can be merged in the application bin folder.
   
9. Go to the "Output Assemblies" tab
10. Select "Merge all pages and control outputs to a single assembly"
11. Call the assembly name: "SharedUserControlMerged"
    
     
12. Build the solution, and see what you get in the Output:
    
    aspnet_compiler.exe...
    Running aspnet_merge.exe ...
    aspnet_merge.exe...
    Successfully merged...
    
    What happens is that the "Deployment Web Project" actually compiles the aspx and ascx files - using aspnet_compiler.
    
    Then merge all dlls (currently we have only one - because we have only one control) using aspnet_merge (which uses ILMerge behind the scenes).
    
13. Now add another Web Project (WebApp.csproj).
14. Add reference to the SharedUserControlMerged.dll from the bin folder of the SharedUserControls.csproj_deploy project.
    
     
    
15. Register this assembly inside a web page on WebApp project.
    
    <%@Register
    tagprefix="xyz"
    namespace="ASP" 
    assembly="SharedUserControlMerged"%>
    
    
16. Now you can use your control on this page:
    
    You need first to find out what is the name of the control in the merged dll.
    I have used Reflector to do it:
    
    
    and just put it in the page:
    
    <xyz:mycontrol_ascx runat="Server"></xyz:mycontrol_ascx>

    
    So what we have is a reusable dll contains our User Control.

    
    Next time we will find out how to create user control with images and JavaScript files.