ASP.NET Web Forms User control cannot find the code behind

Deivid Kirchev 95

Greetings,

This has been going on for quite a bit now and I kind of got used to it but I would be grateful if someone can help me find an answer.

I have an asp.net webforms project with .ascx user controls. For some reason in the markup, it says it cannot find the code behind files meaning some autocompletes don't work and I can't go to the code behind using shortcuts (those are the things which I use the most). The project compiles and publishes without issues and everything works fine.

I have tried quite a bit of solutions online but nothing seemed to work. Last time I was able to fix it by recreating the project, but that is no longer an option as there are a lot of files now.

Thank you for your time!

Lan Huang-MSFT 28,841 Reputation points Microsoft Vendor

2023-08-28T01:37:20.38+00:00

Hi @Deivid Kirchev,

You can try closing and reopening the file from solution explorer.

Or try cutting the page directive line from the page, saving it without it. Paste the page command line back and save again.
Deivid Kirchev 95 Reputation points

2023-08-28T13:48:04.15+00:00

It is not a single file rather all controls in the project, even new ones I am adding. Tried removing the line and pasting it back in - didn't work.

Lan Huang-MSFT 28,841 Microsoft Vendor

Hi @Deivid Kirchev,

There might be an ASP.NET version compatibility issue, you can try changing the .Net version (in project properties) from 4.x back to 3.5 . Or try adding 3.5 compatibility in Web.Config.

<pages controlRenderingCompatibilityVersion="3.5" clientIDMode="AutoID"/>

If you are using .Net 4.0 you can try adding something like this in Web.Config:

<pages>
  <controls>
    <add tagPrefix="asp" namespace="System.Web.UI" assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
    <add tagPrefix="asp" namespace="System.Web.UI.WebControls" assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
  </controls>
</pages>

1 answer

Albert Kallal 5,231 Reputation points

2023-08-25T17:06:58.8333333+00:00

Ok, this came up the other day here. And off and on for many years, I seen this issue.

Now, I have trouble re-creating the issue!

I suggest this:

close all pages and code behind pages

do a clean project.

Now, delete all files in the bin folder

(ONLY do this assuming this is a asp.net web site application - one with .sln file).

So, right click on the solution explorer, and choose open in file explore.

eg:

browse to the bin folder and open it. Now, delete EVERYTHING inside. (so, ctrl-a, and then hit del key).

Now, do a rebuild solution. This:

Now, try opening the aspx page with the ascx control. It should work.
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Deivid Kirchev 95 Reputation points

2023-08-28T13:46:09.2666667+00:00

Sorry for the late response. I have referenced libraries in the bin folder. I tried moving them out, performing the steps you provided, moving them back in, and rebuilding the solution. It didn't work.

Albert Kallal 5,231 Reputation points

2023-08-29T01:15:03.2133333+00:00

Hum, well, that takes some of this suggesting of mine off the table.

You should not have referenced libraries in the bin folder.

Try changing from any cpu to x32, and then re-build, and then open that page in question - see if that helps.

I don't ever place referenced .dll's in the bin folder (it is a really bad idea).

The bin folder is a folder that "should" allow you to re-create from 100% scratch each time you re-build the application. I mean how can you even adopt say git-hub, or any source control system? They (like most applications) will assume that the bin folder can and should be re-created from 100% scratch each time.

Ok, so you have what you have (and can't even really use clean project).

This is also why we see MANY posts stating that starting a whole new project works. It ONLY worked not because you started a new project, but because you started out with a fresh new "empty" bin folder!! You then develop for some time, and it breaks again - and that's often due to stuff piling up in the bin folder.

I would move out your .dll's from the bin folder. I have this setup in my applications:

IMHO project references to .dll's in the bin folder should never have been allowed. However, so many developers simple started dumping .dll's in the bin folder, and thus we live with this setup.

Now, having stated all above, the move out of the .dll's might not fix this, but I find THEN having the ability to clean up the bin folder and re-build from scratch has in near ALL cases fixed the broken property sheet for user controls. (but, this option off the table for you).

Try changing the CPU settings to x32 (x86) and re-build.

That should get you a working property sheet for the UC until such time you re-build (say back to x64).
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ASP.NET Web Forms User control cannot find the code behind

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