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In Visual Studio 2019 Update 16.5 or later you can go to Tools > Options > Projects and Solutions > Build and Run and set 'On Run, when build or deployment error occurs' to one of the options below. Once this is set, running and debugging tests will honor this option as well.
Tools > Options > Projects and Solutions > Build and RunThe selection in the second dropdown “On Run, when build or deployment errors occur”, even if the code has the error during the run, project runs with the last successful build. That's why it should be changed.
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
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:
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.
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 2019, 2017, and 2015.
I cleaned solution, closed VS, reopened it, build solution, and red unresolved lines were cleaned and build succeeded.
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:
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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