Incorrect error "The name XXX does not exist in the current context" appears in Visual Studio

John Mann 41

Recently we have merged four Visual Studio solutions into a single solution.

Since this occurred some of our mark-up code now generates errors when performing a build. The errors appear in the form

CS0103 The name XXX does not exist in the current context nn_ProjectName_FileName

Note the project name appears to be some generated name consisting of a number, the actual project name and the file name (so for example 39_Commerce_PaymentEditor).

HOWEVER this only occurs if the mark-up file is currently displaying on a Visual Studio tab. If the file is closed then the build runs without error.

This is in Visual Studio 2019 and is occurring to all our developers, so it doesn't seem to be environment specific.

Does anyone know why this could be happening and if there is any way to prevent it?

Lex Li (Microsoft) 4,742 Reputation points Microsoft Employee

2021-09-14T14:32:16.17+00:00

Thorough analysis via MSBuild bin log is unavoidable, https://msbuildlog.com/ You need a lot of patience.
John Mann 41 Reputation points

2021-09-29T09:09:40.157+00:00

Sorry I've been away - thanks for the answers let me follow-up on some of the questions.

This is a winforms project - it is building a .NET Framework 4.8 class library.

The top of the .ascx has various Import and Register statements.

Double-clicking on any of the errors goes to the line of code where a control id is being referenced - this could be in JavaScript code or in mark-up.

So here is an example:

Here is some code in the ascx file:

Here is the error:

But the control it says does not exist is declared in the .ascx.cs file

The errors don't appear to stop the build from succeeding - they instead appear to be trying to build extra projects it has auto-generated.

The project name given in the error is always of the form "number underscore namespace underscore control name" so for example "1_Commerce_PaymentCreator" where for example the real project name is "MyProjectName" and the namespace is "MyProjectName.Commerce" - so it is excluding the actual project name and just keeping the remainder of the namespace when it generates this new project name.
Michael Taylor 48,486 Reputation points

2021-09-29T16:05:41.743+00:00

This is a webforms app then, not a winforms app.

The code you gave is a binding expression and they are not evaluated until runtime. At the point the HTML is needed the ASP.NET runtime extracts the server-side code from your ascx file and compiles it into a derived type from your base page/control type. Therefore errors in the .ascx won't be found until runtime.

The errors you're seeing is from the designer trying to make sure your code is correct. It is similar to the way the IDE displays errors before you fully compile. If the code works correctly at runtime then I suspect the designer is out of sync. Deleting the .vs folder may reset everything.

If you're getting runtime errors then you need to ensure you have fixed up all the type names. That would include the .ascx markup file directives and the .ascx.cs file. Additionally you likely have a web.config file (possibly multiples). Within there you normally put your default namespaces so you don't have to import them in every markup file. You should also ensure you have updated your web.config with the new namespaces you are using and remove the unused ones.
John Mann 41 Reputation points

2021-09-29T16:29:13.513+00:00

I installed the BuildLog Extension suggested ("Project System Tools 2017/2019)

I recorded the build and it shows everything with a green tick when I open build log - but it doesn't show any of these generated project names shown in the error messages, just the actual projects in the solution which do indeed build correctly.

I did discover something else that might be of interest.

If all three control windows are open - the ascx the cs and the designer.cs files - then the errors do not appear.

If I closed the designer so just the ascx and cs files were open and rebuilt the errors did not appear.

It seems it is only if just the ascx file is open that these errors appear in the build.
John Mann 41 Reputation points

2021-09-30T08:50:46.44+00:00

Sorry yes winforms was a typo - I meant webforms.

I tried deleting the .vs folder - it didn't make any difference.

As before the errors only occur if just the .ascx file is open without the .cs files - they do not appear if the .ascx file is open with the .cs code behind file (and do not appear if the .ascx file isn't open at all).

Also just to repeat that this wasn't happening until projects in four separate solutions were combined into a single solution - it is only since this happened that I've seen these messages.

2 answers

Michael Taylor 48,486 Reputation points

2021-09-14T14:06:15.73+00:00

There could be lots of causes for this but I'd personally start with just double clicking the error in the Output or Error List window and see where it goes.

Beyond that it is hard to say without seeing some code. You mentioned form but it isn't clear if this is a WInforms or ASP.NET app. These often use resources or other designer-added stuff which uses the default namespace of the project at the point they were added. Therefore if you change namespaces/projects this will mess everything up.

You also mentioned that this only occurs while the designer is open which also pushes me down the path of potentially bad intermediate files so I would also clean the existing code and then do a grep for this specific identifier.
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John Mann 41 Reputation points

2021-09-30T09:09:34.737+00:00

There could be lots of causes for this but I'd personally start with just double clicking the error in the Output or Error List window and see where it goes.

The error takes you to the line in the ascx file where it says the name does not exist.

it isn't clear if this is a WInforms or ASP.NET app.

Sorry for not being clear it is webforms.

Therefore if you change namespaces/projects this will mess everything up.

It does build ok - it just gets bogus errors about names not existing in some weird project name it makes up - the actual project builds fine - I'm just trying not to have a long list of bogus errors when I do a build.

do a grep for this specific identifier

I used Agent Ransack to search every file in the solution folders and subfolders for the weird project name and it didn't' find anything.

Michael Taylor 48,486 Reputation points

2021-09-30T13:48:58.483+00:00

Yes, as I mentioned in the other comment this is a designer error. The binding expression is not being recognized. That code won't actually be compiled until runtime when the control is loaded though. You can read more about how that works here.

Does the control work at runtime? If it does then this is purely a designer issue. Given that if you open the source file the problem goes away then it sounds like a caching problem to me. But since it happens to everyone I have to wonder if maybe you have intermediate files checked into your source control system that would cause them to linger. Specifically you wouldn't have any bin, obj or hidden folders likes .vs in source control. You also wouldn't have .suo or .user files checked in.

John Mann 41 Reputation points

2021-10-01T09:31:20.197+00:00

That sounds plausible - yes it is purely a designer issue - but afaik it happens to every ascx file - I will investigate and see if there were any of those files checked into source control. Thanks for your help!

John Mann 41 Reputation points

2021-10-04T09:41:41.303+00:00

I had a search and we didn't have any of these files checked into source control so that seems to rule that out as an explanation - thanks for the suggestion though.

Michael Taylor 48,486 Reputation points

2021-10-04T16:39:21.217+00:00

Create a new ASCX file, copy the markup and code from the old file(s) to the new ones. Delete the old file and then rename back to the original file names. Does the problem go away for one of the controls?
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Karen Payne MVP 35,036 Reputation points

2021-09-14T14:21:13.47+00:00

Usually for a standard installation of Visual Studio one would use Move type to namespace although this is for code behind. Unsure what markup (to me that could mean HTML, Git or XMAL) you are referring too so perhaps a small code sample might help.
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John Mann 41 Reputation points

2021-10-04T09:43:49.61+00:00

Just to say this sounds like it would require changing of the actual code base which is not ideal given the actual project is building ok and the namespaces are as we want them - all we are looking for is removing these bogus made up projects from being listed and the errors that appear against them.
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