The type or namespace IAppBuilder could not be found(missing using a directive pr an assembly reference)

Question

I am working on an Asp.Net MVC 4 Application in which I am using SignalR 2.0.1 and I Mapped it using Owin Startup class and it worked fine at first.

All of a sudden when I tried to rebuild my app it said that the type are namespace IAppbuilder could not be found.

Following is my start up class

using Microsoft.Owin;
using Owin;
using WhiteBoardApp;

namespace WhiteBoardApp
{
    public class Startup
    {
        public void Configuration(IAppBuilder app)
        {
            app.MapSignalR();
        }
    }
}

I have installed Owin package too, and for some reasons I could not find Owin Startup class so I just added a normal class and included all the references that are needed. May I know where I am making a mistake

Solution 1

Try to use Package Manage Console and do

Update-Package Owin -Reinstall

Solution 2

I was having similar issue. But instead Owin, problem was causing Microsoft.Owin, obviously

Update-Package Owin -Reinstall

Didn't work, neither did Update-Package Owin

BUT

Install-Package Microsoft.Owin

did work fine for me, thanks.

Solution 3

The IAppBuilder interface is found under Owin package. Just add a reference in your class file:

using Owin;

And rebuild. Your project will pick this up.

I have no idea why VS didn't pick this up, but it didn't. Once I added this reference to my project, then everything fell into place.

Solution 4

I encountered the same problem while building my project. Here are the steps that helped fix my problem:

1. Go to Solution Explorer and look for your project
2. Under your project, expand the References; You should see warnings on the problematic reference
3. Right click References and open Manage NuGet Packages
4. Search the name of problematic reference i.e. Microsoft.Owin; After loading it shows that it is already installed (It is, but it installed incorrectly. Checking the properties > version at step 2 shows 0.0.0.0)
5. Check Force uninstall, even if there are dependencies on it
6. Uninstall
7. Install
8. Build and run the project

Problems

Cannot install Microsoft.Web.Infrastructure because it already exists in the packages folder. Rolling back...

1. Go to your project folder and look for packages
2. Find the problematic package i.e. Microsoft.Web.Infrastructure
3. Delete the folder
4. Resume from step 7

Alternatives

Here are the alternatives I've read about to fix this kind of problem.

• Clean and Rebuild Project / Solution
• Restart Visual Studio
• Restart PC

Good luck.

Solution 5

My Visual Studio 2013 for some reason didn't realize that the references paths existed. The yellow exclamation mark in front of the references was shown for all the added packages. I checked ../packages/ but all files existed, i also opened the .csproj file which referenced the correct paths.

Closing and opening the solution returned quite a lot of errors, and could not load the projects included in the solution.

Restarting Visual Studio 2013 saved the day for some unexplained reason.

View more solutions

Comments

[scottt732]

A user suggested an edit to remove the -Reinstall flag. It's probably worth explaining the distinction. The -Reinstall flag will cause NuGet to re-apply the same version of the package that you already have installed. It's like a Repair operation. Generally it will already be in the packages folder and won't need to download. Without this flag, the operation will update the package to the latest version, but only if there is a newer version. Also, this may impact other packages that depend on it. If you already have the latest version installed, I don't think this will do anything.

[JohnB]

I had the same issue. I upgraded to the latest version of SignalR/Owin through nuget. IAppBuilder was not getting resolved. I did the prescribed remedy and the error is gone. BUT.., it pulled down Owin 1.0. Shouldn't we be using the latest and greatest here?

[scottt732]

The Owin package basically contains interfaces defined in the OWIN spec and I as far as I can tell (from owin.org and nuget.org) it's still at 1.0. The Microsoft.Owin package is Microsoft's implementation of the OWIN specification. It's nearing v3.0 but it still depends on Owin 1.0. The Update-Package Owin -Reinstall command causes Owin and any packages that depend on it to get reinstalled. SignalR and WebAPI indeirectly depend on Microsoft.Owin and Owin. After this command gets your builds working again, feel free to update any packages.

[will webster]

I needed a complete reboot

[Rejwanul Reja]

Thanks you MrИво Недев

[Christopher]

I did both of these but the red squiggly wouldn't go away. Then I closed the solution and re-opened it and the red squiggly was gone. =/