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I'm getting a CS0234 "The type or namespace name "Services" does not exist in the namespace" even though I can see it in file structure

I was following a tutorial from Microsoft found at https://learn.microsoft.com/en-us/training/modules/create-razor-pages-aspnet-core/
At one point it instructs to add a folder under the root project called "Services". Within that folder is a file which needs to be accessed. Upon creating the project, another folder called "Models" was automatically created under the root folder.
I include the two lines at the top of another file:
using RazorPagesDoughnuts.Services; using RazorPagesDoughnuts.Models;
The Models statement works no problem. The Services statement generates the error. I have searched many resources and cannot find a solution.
I am using vscode 1.71.2 and .net 6.0
Screenshot of file structure and statements

The namespace provided in the file DoughnutService.cs is probably not correct. Change that to RazorPagesDoughnuts.Services and check.

In C# using statements are not based on file structure, but rather on namespaces. If there aren't any files with the statement namespace RazorPagesDoughnuts.Services in the project, then you will not be able to reference it in other files.
Make sure that DoughnutService.cs contains this namespace statement.

Namespace issues with auto-generated file

After adding to a large Web application a reference to a Web service, the auto-generated Reference.cs is stopping my project from building. Here is the error:
Error 4 The type or namespace name 'XXXXXServiceReference' does not exist in the namespace 'Oranges.Oranges' (are you missing an assembly reference?) C:\XXXXX\Service References\XXXXXServiceReference\Reference.cs
The problem is stemming from the organization of this legacy system. There is a namespace with the same name as the default namespace. So there is a large section declared under namespace: "Oranges.Oranges" for instance. I didn't do it and it's not changing. Bummer.
So when the auto-gen code calls Oranges.XXXXXServiceRequest, ASP.NET looks for XXXXXServiceRequest in Oranges.Oranges and doesn't find it, causing errors.
So I need a way to change the auto-generation or the way ASP.NET is assigning namespaces to this section. I can't risk killing this automatic namespace assumption if it's used elsewhere. This is a very large Web app and I haven't worked on it long.
Any suggestions?

Bummer is right.
BAD SOLUTION: Edit your auto-generated service reference code and add some well-placed global:: keywords in there. Do this every time you re-generate the code.
Note: I feel dirty for even suggesting this. Pleeease be gentle.

1.You may press F2 to rename namespace.
2.Click properties in the solution management and modify default namespace.

The type or namespace name GridViewHelper could not be found

Fist off, I'm very new to ASP.NET and Visual Web Developer Express.
I have a datagrid that I want to display subtotals in and have grouping.
I found this http://www.agrinei.com/gridviewhelper/gridviewhelper_en.htm which looks great. I've added the classes files to my projects App_code folder and re-built the project.
But when I try and use the GridViewHelper I get the error "The type or namespace name GridViewHelper could not be found"
Tried adding using GridViewHelper; to the top of my page but that also gets underlined and the same error.
So how do I tell my project to use the classes I've added?? I think this is a really stupid question but I cant find an answer!

I downloaded the source code from the link you provided, I believe the reason you can't add it is because it is not an actual namespace.
However, in the app_code, they provided a GridViewHelper.cs, just make sure it's in your own app_code file and it should work.

Found the answer here: App_Code folder is missing in VS 2010
So, for Web App Projects, you should instead Add a folder called something like 'CodeFolder' and then add you class in there. Then right click properties on that class file and set its build config to compile rather than content.
It's now working fine.

Compilation errors in Reference.cs after adding a Service Reference caused by multi-part namespace

I hit this weird namespace issue when adding my first 'Service Reference' to a client project in Visual Studio 2010.
If my project's default namespace uses two or more parts, e.g. MyCompany.MyApp then when adding a Service Reference a Reference.cs file is created containing the namespace MyCompany.MyApp.ServiceReferenceName with a lot of auto-gen code with fully qualified names, e.g. System.SerializableAttribute, System.Runtime.Serialization.DataContractAttribute.
The Reference.cs file will be full of compilation errors because the compiler starts treating the System namespace as sub member of the MyCompany.MyApp namespace. You get an awful lot of errors along the lines of:
The type or namespace name 'Runtime' does not exist in the namespace 'MyCompany.MyApp.System'...
If I amend the namespace at the top of the Reference.cs file to something simple, e.g. MyCompanyMyApp.ServiceRefernceName then the compiler behaves and recognises the System namespace references as decleration of .net's System namespace.
I'm using a different workaround for now as I really want to keep my multi-part namespaces. My current alternative is to append global:: in front of the System namespace references to force the complier to do the right thing. In fact, if the 'Add Service Reference' wizard uses T4 templates I may just amend those to embed my workaround at the source.
Questions
I'd really like to understand what's going on here and why a multi-part namespace causes this issue. Presumably there's more to namespaces than I thought. Secondly, would really like to work out a better solution than performing a global Find/Replace every time I add a Service Reference or mucking around with some T4 templates.

I found the answer here somewhat unclear, so I thought I would add this as an example (I would do it in the comments but it looks better here):
So I have this as my default namespace:
namespace RelatedData.Loader
But I also add a class named:
public class RelatedData
{
}
Because the class name matches a portion of the namespace when it generates your proxy with Add Service Reference it gets confused.
The answer here was to rename my class:
public class RelatedDataItem

Ahh well I found the cause eventually.
I'm working against a very large third party WCF API and ... one of their namespaces is LameCompany.System (!!) Carnage then ensues...
Arrrgghhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
The lesson to learn here is when Visual Studio/.net compiler stops recognising the BCL's System namespace you have a namespace/type in your project called System. Find it, remove it, shoot the developer that created it.

I found that having a class name similar to your namespace causes this.
Try renaming your class name

I ran into a similar issue with VS2012 described by jabu.hlong and Simon Needham after minor changes in the client project that has the references to the WCF services after updating the reference to the services. I got lots of errors compiling the Reference.cs files generated and so on (the generated files of the XAML as well).
I have selected to reuse types from specific assemblies in my solution and got a similar problems with the namespaces.
The error I get is that the namespace of the reused assembly and the namespace of the generated types can not be found when used in the Reference.cs. Both namespaces have in common the first parts, as they are from the same solution. My namespaces in the solution are like appname.tier.technology.project. Both conflicting namespaces are Appname.Dto.Modulename (the reused assembly) and Appname.Client.Wpf.ServiceName (the namespace in the client project using the services for the generated types).
The problem arises after a minor change in the client project, when I created a new utility class in the namespace Appname.Client.Wpf.Appname. I choose that namespace because the Appname is also the name of a module in the client project. This seems to confuse the compiler and can not resolve both namespaces in the generated Reference.cs. After changing the namespace of the utility class to avoid using two identical parts in it and updating the service reference, the compiler errors in Reference.cs dissapears.

I tried different things (and tried different namespaces when adding the service reference), but nothing worked for me except this brute force fix - in my case it was OK but I am aware it's ugly (and needs to be repeated if you use "Update Reference" in the future):
Since the WCF service namespace is added to your default namespace, just search and replace all mentions of the newly added
MyNamespace.ServiceNamespace
with
ServiceNamespace
in the whole solution (use your own namespaces of course), including the auto-generated Reference.cs file.

Basically, the problem is a name conflict where one name is hiding another. A folder or class named "System" can do that, but if you also have a class with the same name as your project, you'll see the same thing. Sure, you can rename everything in the reference.cs, but it's probably better to rename your conflicting class.

I had folder in my project called "System" (yes, very stupid of me) and that caused some issues in the references.cs.
Renaming the folder (and the namespace), fixed the issue.

Here is how I solve this issue on VisualStudio 2017 trying to add a reference to a web service in a test project.
After trying adding the references, rebuilding, closing, reopening and spending some time on the issue, I noticed that VS had put the files it creates to reference the WS in a folder named "Connected Services".
I renamed the folder without the space then opened all the files in the folder and the csproj with a text editor, replaced all the occurrences of "Connected Services" to "ConnectedServices" and reopened the project.
I then added references to System.Runtime.Serialization and System.ServiceModel and everything now works fine.

This is a bug in Visual Studio (still is at version 2022). To fix, remove the namespace in the reference.cs file. So if your namespace is "myapplication" and your service is "myservice", you'll see myapplication.myservice in the reference.cs file. just delete "myapplication." everywhere and make sure it isn't auto-generated again (lest you have to re-delete everything).

App_Code folder issues

So I'm having a really weird issue with my App_Code folder on a new website I'm designing.
I have a basic class inside of a namespace in the App_Code folder. Everything works fine in the IDE when I setup the namespace and make an object from the class. It brings up the class summary on hover, and when you click on "go to deffinition" it goes to the class file.
And it also works fine localy.
However, when I load the site onto my server, I get this error message when I access that page:
Line 10: using System.Web.UI.WebControls;
Line 11: using System.Web.UI.WebControls.WebParts;
Line 12: using xxxx.xxxx
Compiler Error Message: CS0246: The type or namespace name 'xxxxxx' could not be found (are you missing a using directive or an assembly reference?)
I know for a fact that the class file is there. Anyone have any idea of whats going on?
Edits:
John, yes it is a 2.0 site.

The problem that your classes are not compiled, You'll solve this issue simply by going to the properties of any class in the App_Code folder and change it's 'Build Action' property from "Content" to "Compile"

If your application is a Web Application project rather than a Web Site project, the code files should not be in the App_Code folder (stupid design, I know). Create a new folder called code or something and put them in there.
It caused me all sorts of problems when I upgraded a bunch of old .Net web sites to application projects.

This just happened to me and the solution was that App_Code (and App_Data) were not put in the root of the server, but in a subfolder that held everything else. Must be in root!

I have noticed a mismatch sometimes between the IDE parser and the compiler whenever a compile-time error occurs in a referenced assembly or code file. In that circumstance the IDE will correctly identify the types and provide full support for them, but since the compiler was unable to create the referenced objects, it will complain that the referenced objects don't exist.
Now I don't want to go accusing anybody of anything—this is just a guess—but you should probably make sure there are not any errors in your referenced code file.

Depending on how you publish the site, it won't look in App_Code, it'll look for a DLL in the Bin folder that contains the class instead. How did you transfer your website to the server?

For those that follow...I had this same set of issues but it was caused because I named a class in App_Code, 'HTML'. Took a long while to figure out that it was just a name conflict because the compiler wasn't being very helpful about telling me what the problem was.