在using语句中无法识别命名空间。 “名称空间'＃'中不存在类型或名称空间'＃'。是否缺少程序集引用？

Question

I have a solution with about 14 projects, and am having a problem with a link I am trying to make between two of the projects:

• Argus.Web (a web application project)
• Argus.Domain.Office.Command (a project that reads data from an API and stores data in a local SQL Server database)
• (there is also a project called Argus.Domain which I mention as it may possibly be part of the problem, although it hasn't caused problems in other similar places in my code.)

Argus.Domain.Office.Command has a context (argusOfficeContext) linking it to a database which I would like to access from Argus.Web. (This context works well in other situations.) When I try to add a using directive to reference the context's namespace in a class within Argus.Web I get the error in the title.

Here is the class I am scaffolding up (in Argus.Web) where the error occurs:

using Argus.Domain.Office.Command.Models;

namespace Argus.Web
{ 
    public partial class Calculator
    {
    }
}

The red wiggly line appears only under 'Office' in the using, and the error in full is "The type or namespace 'Office' does not exist in the namespace 'Argus.Domain'. Are you missing an assembly reference?".

I have checked that the project Argus.Domain.Office.Command is referenced from Argus.Web and when I check Argus.Web build dependencies I see Argus.Domain.Office.Command (as well as the other project Argus.Domain), and it is set to build before Argus.Web. When I check in Argus.Web References > Projects the project Argus.Domain.Office.Command has a tick next to it and I conclude that it is therefore referenced.

Following Peter D's comment I checked the namespace declaration, and it is declared in the project Argus.Domain.Office.Command.

(Probably irrelevant:) here is the class I am trying to reference

using System.Data.Entity;
using Argus.Domain.Office.Command.Models.Mapping;

namespace Argus.Domain.Office.Command.Models
{
    public partial class argusOfficeContext : DbContext
    {
        static argusOfficeContext()
        {
            Database.SetInitializer<argusOfficeContext>(null);
        }

        public argusOfficeContext()
            : base("Name=argusOfficeContext")
        {
        }

        public DbSet<Location> Locations { get; set; }
        public DbSet<LocationPeriodReport> LocationPeriodReports { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            base.OnModelCreating(modelBuilder);
            modelBuilder.Configurations.Add(new LocationMap());
            modelBuilder.Configurations.Add(new LocationPeriodReportMap());
        }
    }
}

Both projects target .NET Framework 4.5.1, and I have looked for the answer in various places, but the fixes for the other questions below don't seem to fix my case. I'm running Visual Studio 2015. Other questions for reference:

• 'Using' not detecting namespace-checked client profiling already
• Visual Studio 2010 suddenly can't see namespace?
• Visual Studio 2015 C# Not finding references

If anyone can advise what I'm doing wrong I would really appreciate it. I have checked lots of other posts looking for an answer, but if you can provide a link to an answer I have missed that would also be great.

Answer 1

Most of the times I see this, the cause is a class with the same name as part of the namespace. These are in two different assemblies.

namespace Library.Foo // assembly 1
{
  using Library.Foo.Bar; // error here

  public class Bar
  {
    public void DoIt()
    {
      new Bell(); // and here
    }
  }
}

namespace Library.Foo.Bar // assembly 2
{
    public class Bell
    {
    }
}

This can be a real pita to find. I suggest doing a test search of each word in your namespace. You're looking for a class of the same name.

As a side (and there's controversy over this), you can avoid some of these collisions by moving the using inside the namesapce .

Answer 2

OK, so I came up with a solution.

I thought I would try removing and recreating the references, and in a nutshell, this worked. Detail:

I right clicked on Argus.Web in the solution explorer, and then Build Dependencies > Project Dependencies. I tried deselecting Argus.Domain.Office.Command, but got the error 'This dependency was added by the project system and cannot be removed'. I'm not sure why this error appears, but I therefore tried right clicking on the references in Argus.Web, and selected 'Add Reference'. In the Projects section of the window that came up I was able to deselect Argus.Domain.Office.Command, so I did this, commented out the problematic using directive, cleaned and rebuilt my solution, added the reference back (right clicking on the references in Argus.Web, and selecting 'Add Reference'), and it all works again.

I guess that the original references must have been misconfigured, but at present I can't see how this came about. I will add to this post if I work out how this happened.

Many thanks to all respondees, all comments and answers were useful.