Develop Reference

Cant recognize class in webform project

In my web form project I opened a folder called App_Code inside that folder I have class named Test123, but when I try to create instance inside WebForm1.aspx.cs it doesn't recognize that type
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
namespace StephanProject_2.App_Code
{
public class Test123
{
}
}
My project structure:
I tried to add using StephanProject_2.App_Code;
What's the problem?

The class you are calling does not seem to be in the same namespace as the Webform1 class
if its from another namespace use.
StephanProject_2.App_Code.Test123 t = new StephanProject_2.App_Code.Test123()
Or alternatively in the top say
using StephanProject_2.App_Code;

When i try to same as your project then it works my code
You can see Here

Microservices in SF: C# can't find type

I'm implementing a number of micrososervices with C# and Service Fabric. All has gone well until this error which seems to be a C# error:
Severity Code Description Project File Line Suppression State
Error CS0246 The type or namespace name 'IProductCatalogService' could not be found (are you missing a using directive or an assembly reference?) ECommerce.API C:\dev\ECommerce\ECommerce.API\Controllers\ProductsController.cs 14 Active
IProductCatalogService is the project ECommerce.ProductCatalog.Model which I have set a project dependency to and I am referencing with a using statement:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using ECommerce.API.Model;
using Microsoft.AspNetCore.Mvc;
namespace ECommerce.API.Controllers
{
[Route("api/[controller]")]
[ApiController]
public class ProductsController : ControllerBase
{
private readonly IProductCatalogService _catalogService;
Here it is ECommerce.ProductCatalog.Model:
using System.Collections.Generic;
using System.Threading.Tasks;
using Microsoft.ServiceFabric.Services.Remoting;
namespace ECommerce.ProductCatalog.Model
{
public interface IProductCatalogService : IService
{
Task<IEnumerable<Product>> GetAllProducts();
Task AddProduct(Product product);
}
}
What am I missing?

From the screenshots above, it looks like you're missing out on referencing to the right project. You want to use using Ecommerce.Productcatalog.Model after you add the reference of Ecommerce.Productcatalog.Model in UI Project.
And from your comments it looks like you have done that and yet you're not able to add that reference. In that case, can you share the screenshot of what it says when you try adding that using statement and also share the project/folder structure if possible, so we can take a look it further.

The type or namespace name does not exist in the namespace (are you missing an assembly reference?)

I know that this question has been already asked, but I cannot find anything that can help solve my problem.
I want to connect my aspx page (Retete.aspx) to a Microsoft SQL database. I'm getting this error on Retete.aspx.cs:
Error 1 The type or namespace name 'GlobalClass' does not exist in the namespace 'ProiectSera' (are you missing an assembly reference?)
The error points to this line of code:
ProiectSera.GlobalClass.Update(ValRefTempSol.Text, ValRefTempAer.Text);
Where ProiectSera is the project name, GlobalClass is the file where I make the operation on the db.
My using statements are:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using ProiectSera;
The Target Framework is set to .net-4.5.
What should I do to solve this error?
Update
My GlobalClass.cs is:
using System;
using System.Data;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data.SqlClient;
using System.IO;
using ProiectSera;
using System.Data.Services;
namespace ProiectSera.App_Code
{
public static class GlobalClass
{
static public void Update(string _param1, string _param2)
{//function to update}
}
}
App_Code is a folder where GlobalClass.cs is. I tried and
ProiectSera.App_Code.GlobalClass.Update(ValRefTempSol.Text, ValRefTempAer.Text); //
but I had the same error. And I put the GlobalClass.cs in the project's root. I also removed the .App_Code from namespace ProiectSera.App_Code
UPDATE1
My Retete.aspx.cs is
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using ProiectSera;
using ProiectSera.App_Code;
namespace ProiectSera
{
public partial class Retete : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
}
protected void btnSave_Click(object sender, EventArgs e)
{
string intValRefTempSol;
string intValRefTempAer;
// intValRefTempSol = ValRefTempSol.Text;
// intValRefTempAer = ValRefTempAer.Text;
// ProiectSera.App_Code.GlobalClass.Update(ValRefTempSol.Text, ValRefTempAer.Text);
GlobalClass.Update(ValRefTempSol.Text, ValRefTempAer.Text);
}
}
}

Your GlobalClass is in the namespace ProiectSera.App_Code.
So the class name is ProiectSera.App_Code.GlobalClass
Make sure you don't have a ProiectSera class in the ProiectSera namespace also, otherwise if declaring using ProiectSera on top, it'll try to use it (as a general rule, don't name any class the same as your namespace).
If that still doesn't work, you may want to try using the global namespace:
global::ProiectSera.GlobalClass.Update(ValRefTempSol.Text, ValRefTempAer.Text);
and see if that works: if it doesn't, and GlobalClass is in the same project, then there's something else you haven't shown us
Update
The only other thing that comes to mind, if you are positive that both files are on the same project/assembly, is that GlobalClass.cs is not being actually compiled. Make sure the Build Action is set to Compile (you can see the build action right clicking on the GlobalClass.cs in the solution explorer and selecting Properties).

If you are using VS.NET:
Right click on the References folder on your project.
Select Add Reference.
Select the .NET tab (or select the Browse button if it is not a .NET Framework assembly).
Double-click the assembly containing the namespace in the error message.
Press the OK button.

Ensure the following...
That you have a project reference to ProiectSera from your web application, if it's in a separate library. If GlobalClass is in the web application project itself, you won't require this, but if GlobalClass is defined in a separate library in the same solution or elsewhere, then you're going to need to add a reference to that external library in your web application.
Ensure that ProiectSera should not be ProjectSera (if it's a typo).
Ensure that you have your ProiectSera using statement in place at the top (using ProiectSera;). Assuming that this is the correct namespace. Check the namespace of your GlobalClass class and use that using accordingly in the class that wishes to use its functionality.
Then, simply call this in your code, assuming that Update is a static method of GlobalClass.
GlobalClass.Update(ValRefTempSol.Text, ValRefTempAer.Text);
EDIT: given that you've now posted your GlobalClass code, you can see that the namespace for this class is ProiectSera.App_Code;. So you need to have that as your using statement in the other class using ProiectSera.App_Code;. And then call it via simply GlobalClass.Update, as mentioned above.
If you don't understand how namespacing works in C#, then I recommend you check this out (https://msdn.microsoft.com/en-us/library/dfb3cx8s.aspx).

Application can't find OWIN Startup class after rename

So I renamed my MVC application from "Conclusion" to "ConclusionWeb" to avoid namespace errors. Since doing so I get the error "No assembly found containing an OwinStartupAttribute.". When I go to Properties the drop-down list to select a Startup Object is empty. I've added all the niceties I can find to my Startup class, below, but it isn't being detected. Any ideas?
using Microsoft.Owin;
using Owin;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
namespace ConclusionWeb.App_Start
{
[assembly: OwinStartup(typeof(ConclusionWeb.App_Start.Startup))]
public class Startup
{
public void Configuration(IAppBuilder app)
{
}
}
}

Why Visual Studio say to me that the type or the namespace name could not be found?

I am very new in C# (I came from Java) and I have the following problem
I have a solution that contains some project.
One of this project contain a class named CpeManager, this is the code:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data;
using System.Diagnostics;
namespace DataModel
{
class CpeManager : MyManagerCSharp.ManagerDB
{
public CpeManager(string connectionName)
: base(connectionName)
{
}
public CpeManager(System.Data.Common.DbConnection connection)
: base(connection)
{
}
}
}
Then in another project (that is into the same solution) I have a class that contains a reference to the previous CpeManager class, something like it:
DataModel.CpeManager manager = new DataModel.CpeManager("DefaultConnection");
My problem is that Visual Studio give me the following error message on the previous line
The type or namespace name 'DataModel' could not be found (are you missing a using directive or assembly reference?)
What is the problem? How can I solve it?
Tnx
Andrea

You need to add a reference to the project which contains the Datamodel namespace. You do this by right clicking your project which requires it and selecting add reference, locate your project with DataModel in and add it in.
EDIT: As Tim noted you also need to make your CPEManager class public if you want to then be able to access it

Make CpeManager public.
public class CpeManager : MyManagerCSharp.ManagerDB
{
// ...
}