Visual Studio displaying errors even if projects build

If you have ReSharper, try emptying the ReSharper cache:

In menu, ReSharper > Options > Environment > General > Clear Caches

and disabling and re-enabling ReSharper:

In menu, Tools > Options > ReSharper > General > Suspend / Restore

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Clearing Resharper's cache did not help in my case, tried suspend/restore, and also Repair Resharper, using latest download off JetBrains' website - neither of these helped. This is after I tried close/reopen VS, restart my machine, repeat, Build/Rebuild and combination thereof.

It's interesting that suspending Resharper seemed to solve the problem after the 2nd restart of VS, but it was back after I enabled Resharper <-- I tried to do this sequence 2-3 times to ensure the pattern.

Anyway, I was still having issues when I found this article:

Quick tip: What to do when Visual Studio freaks out and everything is red

So I deleted the hidden .SUO file on the same folder level with solution, and it magically solved all reds.

Note - for Visual Studio 2015, the .SUO file is in .vs/[solution_name]/v14 hidden folder.

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tldr; Unload and reload the problem project.

When this happens to me I (used to) try closing VS and reopen it. That probably worked about half of the time. When it didn't work I would close the solution, delete the .suo file (or the entire .vs folder) and re-open the solution. So far this has always worked for me (more than 10 times in the last 6 months), but it is slightly tedious because some things get reset such as your build mode, startup project, etc.

Since it's usually just one project that's having the problem, I just tried unloading that project and reloading it, and this worked. My sample size is only 1 but it's much faster than the other two options so perhaps worth the attempt. (Update: some of my co-workers have now tried this too, and so far it's worked every time.) I suspect this works because it writes to the .suo file, and perhaps fixes the corrupted part of it that was causing the issue to begin with.

Note: this appears to work for VS 2022, 2019, 2017, and 2015.

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I cleaned solution, closed VS, reopened it, build solution, and red unresolved lines were cleaned and build succeeded.

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I found that happens frequently when using Git in Visual Studio 2017, switching branches where there is dependent code changes. Even though the project will build successfully, there will remain errors in the error list.

These errors are often namespace issues and missing references, even when the library reference exists.

To resolve:

Close Visual Studio

Delete the {sln-root}.vs\SlnName\v15.suo file (hidden)

Restart Visual Studio

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I have tried all the 6 options, nothing worked for me. Below solution resolved my issue.

Close VS. Delete the hidden ".vs" folder next to your solution file. Restart VS and load the solution.

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Here's a collection of popular answers. Upvote the OP of the answer if it helped you:

Option 1: Clean, Build and Refresh (@Mike Fuchs option)

As @Mike Fuchs mentioned, try the following operations:

In menu, Build > Clean Solution And In menu, Build > Build Solution

and select the project in question, and click on the refresh button:

https://i.stack.imgur.com/iZ1Gd.png

Option 2: Clean, Close, Restart and Build (@Pixel option)

As @Pixel mentioned, try the following sequence of operations:

Clean the solution Close Visual Studio Open Visual Studio Build solution

Option 3: Clear ReSharper cache (@GammaOmega option)

If you have ReSharper, try emptying the ReSharper cache:

In menu, ReSharper > Options > Environment > General > Clear Caches

and disabling and re-enabling ReSharper:

In menu, Tools > Options > ReSharper > General > Suspend / Restore

Option 4: Delete the .suo file (@Neolisk option)

As @Neolisk mentioned, deleting the .suo file might solve your problem. For Visual Studio 2015, the file is located in:

[Path of Solution]/.vs/[Solution Name]/v14/.suo

And for Visual Studio 2017:

[Path of Solution]/.vs/[Solution Name]/v15/.suo

Note that the .vs directory is hidden.

Option 5: Unload and Reload Project (@TTT option)

As @TTT mentioned, try unloading the project that causes problems:

In Solution Explorer, right-click on project, Unload Project.

And re-loading it

In Solution Explorer, right-click on project, Reload Project.

Option 6: Remove and add Microsoft.CSharp reference (@Guilherme option)

As @Guilherme mentioned, try removing and adding the reference to "Microsoft.CSharp" from the projects that have problems.

In Solution Explorer, expand the project, expand "References", right-click on "Microsoft.CSharp" and Remove. Then, right-click on References > Add Reference, select "Microsoft.CSharp" from the list and click OK

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Delete the hidden file path = your solution\ .vs\ your solution Name \v15\ .suo

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I had a problem like this where Intellisense didn't seem to recognise the existence of one project (lots of "can't find this type", "this namespace doesn't exist", etc. errors).

Removing and re-adding the project reference in all the referencing projects would fix the issue, but the underlying cause could be fixed by editing the .proj file of the problem project.

Near the top of the "missing" project' .csproj file is an element:

<ProjectGuid>{GUID}</ProjectGuid>

and in all of the referencing projects .csproj files were project references:

<ProjectReference Include="..\OffendingProject\OffendingProject.csproj">
  <Project>{ANOTHER-GUID}</Project>
  <Name>Offending Project</Name>
</ProjectReference>

The referencing GUID didn't match the project's GUID. Replacing {GUID} above with {ANOTHER-GUID} fixed the problem without having to go through every referencing project.

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So many things that could cause it, as evidenced by the long list of answers here. Here's what fixed it for me, having tried pretty much everything else first.

Build your sulution in DEBUG mode. Then build it in RELEASE mode (it shouldn't build when it has red wavy lines, but in my case it was just warnings that should have had green wavy lines but it was getting in a muddle and giving them red wavy lines, and it built anyway even in release mode). Then build in in DEBUG mode. Spitting on your hands and turning around three times optional.

Worked for me, when nothing else did.

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for VS-2017, deleting .vs folder worked for me.

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I've noticed that sometimes when switching git branches, Visual Studio (2017) will not recognize types from some files that had been added in the second branch. Deleting the .vs folder solves it, but it also trashes all your workspace settings. This trick seems to work well for me:

Solution Explorer -> Find the file with the unrecognized class in it. Click Show All Files at the top of the Solution Explorer. Right-click the file -> Exclude from project. Right-click the file again -> Include in project.

This causes Intellisense to parse the file that it missed when switching branches.

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Occasionally I have to do a custom clean by going through all of the projects and manually deleting the "bin" and "obj" folders. To see them in Visual Studio, you'll have to enable hidden files and folders for each project. After this is done, rebuild the solution.

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Following solution worked for me

1 - Close VS

2 - Delete .vs folder

3 - Open VS

4 - Build solution

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Perhaps you try to reset your intellisense cache. I've had a similar issue in visual studio 2012 when working in a large project with many partial class definitions. Reducing the partials solved the problem partially, clearing the intellisense cache also - for a while.

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Deleting .vs folder solved my problem.

But it also reset my solution's current settings in VS. Like, my unloaded projects in the solution were re-loaded and all the pinned and opened documents were also closed when I restarted the VS.

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My symptoms in VS2019 were that I would build with some errors. Then I'd fix the errors, and the build would work, as shown in the Output window. But the Errors windows still showed the old errors. I could run it just fine. Closing VS2019 and reopneing fixed the issue, but only for a little while. This started happening on version 16.4.3

This solution seems to work for me:

Uncheck Tools->Option->Projects and Solutions->General->Allow parallel project initialization

I found this fix buried way down in the comments here: https://developercommunity.visualstudio.com/content/problem/483450/vs-2019-intellisense-reports-compile-errors-when-r.html

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0 - Right click on the Solution and clean solution

1 - Close VS

2 - Delete project's .suo file

3 - Open VS

4 - Build solution

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A colleague of mine experienced this issue today. We tried many of the recommendations here and none worked except the solution described below.

Problem:

Project builds fine but Intellisense fails to recognize certain types and marks particular using statements as invalid.

Solution:

Change the 'Solutions Platform' (in VS 2017 this is the dropdown next to the Solution Configuration dropdown and has values such as x86, x64, AnyCPU, Mixed Platforms, etc.) to AnyCPU.

The platform for your project may vary, but it seems as though some references may not be valid for all platforms.

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In my case helped a combination of things:

deleting all old not needed files which were previously excluded from the project closing VS deleting all the bin folder contents deleting .vs folder Clean/Rebuild after that I still had some spurious errors, however the amount was significantly lower (from 200 to around 8) and the errors referred only to a resource dictionary path in Generic.xaml e.g. when I played around with the path trying to change it to a wrong one re-building then correcting it and rebuilding again, then this finally cleared all errors. It was specifically WPF project if that's relevant.

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For my specific case it was a service reference another developer merged into the main branch. Which was perfectly fine except syntax highlight failed to resolve the generated service class and source was all red underlined. Cleaning, rebuilding, restarting did nothing.

All I had to do was refresh the service reference and VS managed to put the pieces together behind the scenes. No changes in the source code or generated files.

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I've just ran into this issue after reverting a git commit that added files back into my project.

Cleaning and rebuilding the project didn't work, even if I closed VS inbetween each step.

What eventually worked, was renaming the file to something else and changing it back again. :facepalm:

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After trying all of the options listed I discovered yet another reason why this can happen. If somebody sent you the source code as a zip, or you downloaded a zip, Windows may have blocked all files. 2 ways to solve this:

Method 1:

Right click on the original Zip file -> Check 'Unblock' -> Click apply

Method 2:

If that's not an option, rather than opening properties on every file in the solution folder simply open power shell and unblock recursively using the following:

Get-ChildItem -Path 'C:\<ROOT FOLDER OF SOLUTION>\' -Recurse | Unblock-File

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first close the solution. then solution cache file delete( in location C:\Users\Documents\Visual Studio\Backup Files/project cache file) then .suo file delete then solution open and build.

I hope solve your problem

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Had this issue at work (running VS2017). Tried all of the answers here. No joy.

The project would build just fine, but was complaining that namespaces / types couldn't be found. Red squiggles all over the place. Lots of errors in the Error List window.

My solution contained 3 projects.

Discovered that 3 of the NuGet library references for one of the projects was out of line. Consolidated the referenced library versions, and Bingo.

Hope this helps someone.

Brett.

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Unload & reload the project fixed this problem.

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I've been struggling with this issue for over a year and none of these solutions helped me:

Delete .suo

Delete .vs folder

Delete any or all cache / temp folders

Delete obj / bin folders

Unload / reload project

I finally fixed this issue - I opened the vbproj/csproj file in notepad and noticed that in the ItemGroup section, there was a reference back to my main project dll. I deleted this reference, reopened my solution and the problem was fixed.

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Sometimes if you just clean solution the errors are disappearing, but they may eventualy come back afer a while or at the next build.

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Ran into this issue with a single type not being recognized by Visual Studio which showed the red squiggle even though the solution built successfully. I noticed in the Solution Explorer the file did not have the expand arrow on the left which shows classes and properties on expansion.

The fix was to Exclude the file from the project and save/build which produced an expected error and then Include the file in the project and save and build.

After performing these steps Visual Studio started to recognize my type again. Looking at the diff in git it appears the issue was due to line endings not matching on the <Compile Include="..." /> line of my .csproj file.

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in my case vs was never retaining the imported namespaces in the project properties > references

when I tried to add/check them again I couldn't and vs threw an error and when saved project vs crashed. When I reopened all the standard imported namespaces (system.data etc...) were all ticked again and it then was recognising everything without error

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