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vs 2017 intellisense not working C# and XAML

I have a Strange issue that I can't seem to fix, my Intellisense for XAML is no longer showing up and the code behind is only showing the premade Members. The Classes and Methods I have made are not showing up. Also Visual Studios is not recognizing other pages and wont recognize Navigation either.
I have tried going to Tools>Text Editor>C#>Intellisense -Statement completion and checking the boxes Auto list members and Parameter information. I also tried to clear out the cache.
From what I have researched it seems nobody else is having the same problems.

Close all open tabs in the project and quit VS, reopen the solution in VS and right click the XAML file in the Solution Explorer and then select Open With….> Source Code (Text) Editor.
Delete obj folder and clean project
Right click the XAML page>Properties>Build Action>change it to something else and back
Add a new content page under this specific project and check it works or not.
I would like to add that this worked for my .cs files only.
To get the XAML files Intellisense to work try to repeat the above steps on your .cs files or wait for the XAML files to gain Intellisense.

For ReSharper users: I found that having ReSharper's IntelliSense enabled for all languages can break Intellisense unexpectedly (especially for XAML files). Here's how I was able to fix the same problem that the asker had in Visual Studio 2017 with ReSharper installed:
In Visual Studio, go to the ReSharper menu and click on Options.
On the left side go to Environment > IntelliSense > General.
Select the Custom IntelliSense radio button.
Change any languages that have broken IntelliSense to Visual Studio (like XAML).
Click the Save button.

Just Exclude and Include Xaml Pages and It works again.

I solve that by changing the default editor in visual studio :
In Visual : File > Open
In the open file box : Select a .xaml file (don't open it)
Select "Open with" in the button arrow
Select "Source Code (Text) Editor and Set as Default
Click OK

I tried most of the above without much luck, but noticed if I created a new page, then intellisense worked as expected. For the properties section of the xaml file I noticed that the new page had a Custom Tool assigned (MSBuild:UpdateDesignTimeXaml) do I tried to cut-and-paste this into the existing forms without luck.
Looking at the .cs page for the new page that worked I notice that there is some extra info above the partial class [XamlCompilation(XamlCompilationOptions.Compile)] so I added this along with a using Xamarin.Forms.Xaml statement.
Finally I went back to the xaml properties page and selected Reset to Default for the Custom tool. Voila, for me everything started behaving itself.

Please add the following Nuget Package from Nuget Console.
Install-Package MobileEssentials.FormsIntellisense -Version 0.1.1-pre
You can download the latest update from the following link.
https://www.nuget.org/packages/MobileEssentials.FormsIntellisense/0.1.1-pre
After installing the package please restart the project and wait for sometime and check it.

Just delete .vs directory. this directory is hidden. so

Just Exclude and Include Xaml Pages worked for me too. The difference in .csproj file was:
MSBuild:Compile
now:
XamlIntelliSenseFileGenerator

I could fix the issue in VS2019 by launching the VS installer to modify it, un-check and check the workload ‘.NET desktop development’ to re-install it.

Import Project to Immediate

Having just installed VS2015 Update 1, I discovered the C# Interactive window.
According to the second post in that series, you should be able to import a project from your solution.
When you want to fire up the C# Interactive Window you can just right click your solution and select "Reset Interactive from Project"
However, this option is not available on my project. I'm using a Console Application to test, and have pushed the framework up to 4.6.1 from 4.5. However, this has not worked.
Additionally, I have attempted to manually import the project. Looking at the screenshots on the website, I should be able to do this like this: #r "ConsoleApplication7.exe" but when I do, I get the following exception:
(1,1): error CS0006: Metadata file 'ConsoleApplication7.exe' could not be found
It will pull in via the filepath, e.g:
#r "bin\Debug\ConsoleApplication7.exe"
However, this is a little unwieldly. Especially since whenever you make changes to the classes, it requires a #reset and re-import.
Is there a better way to import Projects into the Immediate instance?

According to the Comment from Jason Malinowski
It doesn't really answer your question, but unfortunately we had to cut the "Reset from Project" command in Visual Studio 2015 Update 1 just because we were crunched getting everything else done. We don't like that it's not there either.
Jason Malinowski
Therefore, at this time (2016-02-04), the "Reset from Project" option is not available.
Projects can be imported manually, by using the following command:
#r "bin\Debug\ConsoleApplication7.exe"
This should work when you are running the REPL with the solution open in the same instance, and when you have only one project.
At other times, you will need to use the full file path
#r "C:\MySolution\ConsoleApplication7\bin\Debug\ConsoleApplication7.exe"

Can't change a project's Default Namespace in Visual Studio 2013

I have a solution that includes various C# projects, and I just now noticed that I can't change the default namespace on any of them.
When I go to Properties --> Application on any of the project and change the "Default Namespace" field, a fatal error dialog pops up that says:
exception of type 'system.runtime.interopservices.externalexception' was thrown
At this point Visual Studio becomes unusable, as I can't close it or leave the screen, every click or button combination I press makes the same dialog pop up. The only thing I can do is terminate VS with the task manager.

I got around it by just renaming the <RootNamespace> node in the .csproj file

Maybe you should try to do this in another way:
Ctrl-H - Find: PreviousNameSpaceName Replace: NewNamespaceName
You can also right click the namespace in code and Refactor->Rename.
What is more: you can change the names of your projects, solutions, directories - etc. Namespaces, when adding new files, are generated using these names in fact.

I had to investigate the issue in our company and I found another workaround in our case. So I think it make sense to add it here.
Possible Solution
Check if you have more than one suo-File for the project/solution and delete the one which doesn't has the ".v12.suo" naming (better delete both)
Story behind:
We still have two Visual Studio installed (2010 and 2013) and some of our developer worked recently on 2010. So they had on the file system a regular ".suo"-File. Afterwards (some weeks later) they started to use 2013 (which created a ".v12.suo"-File).
We renamed both suo files, started VS2013 (which created the v12.suo) and were able to rename the namespace without a crash. In addition we had this issue not on all solutions. I didn't see yet a pattern, but in our case it happened mostly on solution with at least two projects and referenced project-libraries.

C# Debug - cannot start debugging because the debug target is missing

I am fairly new to C#..
I am using Visual Studio 12, the source I am using was last edited in VS 12.. But my problem is that it's throwing me this error:
First of all, my computer username isn't Martin, it is Administratoring - The creator of this project is Martin.. So that's where I guess it's coming from, but I don't know how to fix this.
I have tried editing in Project > Properties > Build > Output Path - And it still doesn't work. I am not too familiar with C#, and I've spent some time searching up for a solution but can't find it anywhere.. Probably because I don't know what I should be searching up (I've tried searching keywords and quotes from the error, but still nothing)

Try these:
Make sure that output path of project is correct (Project > Properties > Build > Output path)
Go in menu to Build > Configuration Manager, and check if your main/entry project has checked Build. If not, check it.

For those with this kind of problem - another solution:
Pay attention also to Warnings when you build solution. For example, I had referenced a dll built with higher version of .NET (4.5.2) than my main project (4.5)
After I referenced a dll built with 4.0 build process was successful.

Please try with the steps below:
Right click on the Visual Studio Project - Properties - Debug - (Start Action section) - select "Start project" radio button.
Right click on the Visual Studio Project - Properties - Debug - (Enable Debuggers section) - mark "Enable the Visual Studio hosting process"
Save changes Ctrl + Shift + S) and run the project again.
P.S. I experienced the same problem when I was playing with the options to redirect the console input / output to text file and have selected the option Properties - Debug - (Start Action section) - Start external program. When I moved the Solution to another location on my computer the problem occurred because it was searching for an absolute path to the executable file. Restoring the Visual Studio Project default settings (see above) fixed the problem. For your reference I am using Visual Studio 2013 Professional.

I had the same problem and unfortunately non of above answers worked for me . the solution that worked for me is :
right click on your startup project and select Properties - Debug and change "start external program: " to the correct path
Done!

Switch Target framework to 4.5.2 or something higher and bring it back to your original version (example: 4.5) then when you build, it will work.

You are not set the startup project so only this error occur. Mostly this problem occur when your working with more project in the single solution.
First right click on your project and "Set as Start Up Project" and/or right click on the start up file inside the selected project and click "Set StartUp File".

I also get this error quite often.
I solve this by modifying the code (doing a very small change), saving it, then building the solution again.

In my case I had added a project to a solution manually, where that project was targeting a higher .NET version than the rest of the projects that were referencing it. Strange... there would normally be a somewhat more verbose, literal and descriptive error in such cases.
There wasn't a real error but there was a warning that said as much.

Go to Project > properties > Debug Tab and set the Launch to "Project"

I had the same problems. I had to change file rights. Unmark "read only" in their properties.

So... it’s mid 2021 and I’m using visual Studio 2019 (version 16.10.2) which is the current version available, on a windows 10 pc.
I had to start a new project and following this steps solved the issue;
When at the menu that says “Create new project”
After you’ve selected your project template it takes you to another menu that says “Configure your new project”
On this menu there’s an option that says “Place solution and project in the same directory”.
By default this option was not checked, so I checked it and it solved the issue.

I had the same problem with visual studio 2015 , and I found that there is reference is marked so I just deleted it , maybe you can delete this reference or reinstall it again

What solved it for me was deleting the line
<ImplicitUsings>enable</ImplicitUsings>
from the project property file. It caused Visual Studio to generate a (useless) file with multiple global using directive.

I faced the same problem , but in my solution i had many projects so in the solution configuration the start up project was by mistake a class library i changed the startup project and then i worked like a charm
right click on the sln => common proprties => choose right startup project .

How to find the reason for a failed Build without any error or warning

I have a WebApplication which contains reference to WCF services.
While building using Visual Studio 2010, Build fails without any error or warning. However building the .csproj using MsBuild is successful.
Can't figure out what should I try in Visual Studio, to resolve / diagnose the issue. Can you please help out?
I find out that the build has been failing,
From text displayed in status Bar.
From output window:
========== Build: 0 succeeded or up-to-date, 1 failed, 0 skipped ==========
The output tab includes configuration details.
------ Build started: Project: <projectName here> Configuration: Debug Any CPU

I noticed that if "Build + Intellisense" is selected in the Error List, it causes the error messages to be swallowed.
Change this option to "Build Only", and all error messages will be displayed:
I don't know if this is a bug in Visual Studio or what, but it certainly revealed hidden error messages that were the key to pinpointing the failure for me.
Some, like Richard J Foster, have suggested increasing the "MSBuild project build output verbosity" setting to "Diagnostic" (the highest possible option), but this didn't solve the problem for me, as Visual Studio appeared to be suppressing the error message(s) themselves.
As an alternative, you may try to use the raw output messages from the "Output" tab, which haven't been filtered by Visual Studio. Either do an in-place search for the strings "error" and/or "failed", or copy all of the output to your favorite text editor and do a search there.
To ensure that the Output window appears each time you do a build, you can go to Tools → Options → Projects and Solutions → General, and ensure that the option "Show Output Window when build starts" is checked.
As an additional troubleshooting step, it is also possible to build the project from the PowerShell command line by running dotnet build. This will show you the complete build output, including any errors that Visual Studio may be hiding.

I just ran into a similar situation. In my case, a custom action (from the MSBuildVersioning package available on Nuget.org - http://www.nuget.org/packages/MSBuildVersioning/) which appeared in the csproj file's BeforeBuild target was failing without triggering any error message in the normal place.
I was able to determine this by setting the "MSBuild project build output verbosity" (in the latest Visual Studio's Tools tab [Path: Tools > Options > Build and Run]) to "Diagnostic" as shown below. This then showed that the custom action (in my case HgVersionFile) was what had failed.

Here are some things that you can try:
If your solution contains more than one project, try building each project one at a time. (You may even want to try opening each project independently of the solution.)
If applicable, ensure that all of your projects (including dependencies and tests) target the same version of the .NET Framework. (Thanks to user764754 for this suggestion!)
Tip: Check Tools → Extension and Updates to ensure that your packages are up-to-date.
Ensure that all dependency projects are built to target the same platform as your main project.
Try restarting Visual Studio.
As suggested by Bill Yang, try running Visual Studio as Administrator, if you aren't already. (If you are already running Visual Studio as Administrator, perhaps try the opposite?)
Try restarting your computer.
Try "Rebuild All".
Run "Clean Solution", then remove your *vspscc* and *vssscc* files, restart Visual Studio, and then "Rebuild All".
As suggested by Andy, close Visual Studio, delete the .suo file, and restart Visual Studio.
As suggested by Arun Prasad E S, close Visual Studio, delete the .vs folder in your solution directory, and then re-open Visual Studio. (This folder is auto-generated by Visual Studio and contains cache, configuration settings, and more. More details can be found in these questions: Visual Studio - Deleting .vs folder and https://stackoverflow.com/q/48897191.)
As suggested by MrMalith, close Visual Studio, delete the obj folder in your solution directory, clear your temporary folder, and then re-open Visual Studio.

Delete the hidden .vs folder & restart Visual Studio. That worked for me.

I want to expand on Sasse's answer. I had to target the correct version of .NET to resolve the problem.
One project was giving me an error:
"The type or namespace name 'SomeNamespace' does not exist in the namespace 'BeforeSomeNamespace' (are you missing an assembly reference?)".
There was no error in the Error List window but the assembly had a yellow warning sign under "References".
I then saw that the referencing project targeted 4.5.1 and the referenced project 4.6.1. Changing 4.6.1 to 4.5.1 allowed the overall build to succeed.

Nothing was working for me so I deleted the .suo file, restarted VS, cleaned the projected, and then the build would work.

I tried many things like restarting Visual Studio, cleaning and rebuilding the solution, restarting the PC, etc., but none of them worked for me. I was finally able to solve the problem by doing the following:
First of all, make sure all the projects in your solution (including tests) are targeting the same .NET version. Then:
Save pending changes in the project and close Visual Studio
Find the exact location from file explorer and find "obj" file and open it,
Then, delete all the included files (some files won't remove, it doesn't matter, just skip them).
Use run command (by pressing Windows Key + R) and type "%temp%" and press enter to find temporary files.
Finally, delete them all.

On other possibility is that Visual Studio needs to run as Administrator, this might be related to deploying to local IIS server or other deployment need.

Just for the sake of completion and maybe helping someone encountering the same error again in the future, I was using Mahapps metro interface and changed the XAML of one window, but forgot to change the partial class in the code-behind. In that case, the build failed without an error or warning, and I was able to find it out by increasing the verbosity of the output from the settings:

In my case (VS 2019 v16.11.20), disabling Text Editor->C#->Advanced->Enable 'pull' diagnostics in the options solved the issue.

Double check for _underscore.aspx pages in your project.
I had a page and code-behind:
`myPage.aspx` and `myPage.aspx.vb`
when building the project, I'd get errors on the .aspx.vb page stating that properties defined on the .aspx page didn't exist, even though the page itself would build fine and there were NO OTHER ERRORS showing in the output (even with diagnostic level build output).
I then came across a page in the project that was named the same thing but with an underscore: _myPage.aspx - not sure where it came from, I deleted it, and the solution built fine.