Develop Reference

UWP System.Reflection.TargetInvocationException when including a view in a page?

I have 2 pages. One page contains another, where the Grid looks like the following:
<Grid>
<views:MapViewPage/>
</Grid>
I've included the views namespace correctly and everything runs fine but the designer seems to be having a bit of an issue with this.
It underlines the views:MapViewPage line and says object reference not set to an instance of an object, and complains about the constructor. I don't understand why, I've done this in WPF where I've included views in another page or window so I don't understand why the XAML designer complains in UWP. I've restarted visual studio and deleted the bin and obj directories but i still see the error - builds fine and runs fine tho... and includes the view as expected...

You are on the right path but sometimes designer picks up wrong metadata. Please delete your obj and bin directories and rebuild your project. It should work

It underlines the views:MapViewPage line and says object reference not set to an instance of an object, and complains about the constructor.
Yep, this is common behavior, if you just create folder and make a xaml file in it then use xaml file without build the project, the Visual Studio will not find the specific the namespace (xmlns:views="using:projectname.Views"). Please try to
restore the nuget package (right click the solution Restore Nuget Package) and build or re-build your project before running it.

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"

Visual Studio compiles fine, but it still shows red lines

I am using Visual Studio 2012 and it was working all fine until I started observing some funny behavior. When I open my code it shows red Underlines which we usually see when there is an error in our code. Surprisingly, the code compiles all fine. I have made following observations that are not normal at all.
Red underlines in the code
While cleaning or building the solution no error.
Red underlines go away for some time after I build/clean the solution, but they come back eventually.
Because of this, my IntelliSense stopped working.
I can not right click on any component and go to its definition.
Any ideas?

Visual Studio 2017, Visual Studio 2019, Visual Studio 2022:
Closing Visual Studio and removing the .vs folder located in the solution directory worked for my C# projects.
This folder has a hidden attribute. You may need to change View settings to show hidden files in File Explorer.

Delete the contents of the temporary ASP.NET folder and then rebuild. It'll either be in your user folder (for IIS Express - \AppData\Local\Temp\Temporary ASP.NET Files) or the Windows directory (for IIS - C:\Windows\Microsoft.Net\Framework\vx.xx\Temporary ASP.NET Files)
Paths are off the top of my head and may not be correct

For me, this issue got fixed when I unloaded and reloaded the project again.

I had this issue and it was related to ReSharper.
Solution steps for me:
Disable ReSharper
VisualStudio\Tools\Options\ReSharper Ultimate\General\Suspend Now
Build Solution
(Ctrl + Shift + B)
Re-enable ReSharper
VisualStudio\Tools\Options\ReSharper Ultimate\General\Resume Now

Just had this problem while working with a solution created in Visual Studio 2012 but running in 2013. I closed Visual Studio, deleted all \bin and \obj directories and the problem was gone.

I had this problem after resolving some conflicts from Subversion (SVN). The solution has several projects in it and I resolved some conflicts in a few different projects. I did a menu Build → Clean Solution followed by a men Build → Rebuild Solution and everything was good again.

Do you have any plugins installed, like ReSharper? I had an issues with a bad plugin.
Try running Visual Studio in safe mode, to prevent plugins from running.
devenv /Safemode

If you are using ReSharper like me, you may delete ReSharper cache following by this link: Configure Caches
To specify the location for caches:
Open the Environment → General page of ReSharper options.
Use the Save solution caches in to select the location for cache files:
User local settings folder to store them in the following directory: %LOCALAPPDATA%\JetBrains\Transient
4.System TEMP folder to store them in the following directory: %TEMP%\ReSharperCache
Solution folder to store them in the root folder of the current solution
Custom folder to choose a custom location for ReSharper cache files.
Click Save to apply the modifications and let ReSharper choose where to save them, or save the modifications to a specific settings layer using the Save To drop-down list. For more information, see managing and sharing ReSharper settings.
Reopen your solution for the changes to take effect.

What works for me is deleting the IntelliSense indexfile.
The IntelliSense-file is in the same directory as you solution.
It's filename is SolutionName.sdf
Just delete this file, open you solution again, and IntelliSense will start rebuilding its indexfile. After that the problem will be gone.

In Visual Studio 2013 I solved this problem by deleting all of my obj and bin folders across all projects. The issue was probably due to solution configurations that I had deleted, but I hadn't been cleaned up properly, as doing a menu Build → Clean Solution doesn't remove the old outputs from the obj and bin folders.

This worked for me in Visual Studio Enterprise 2017:
Navigate to Tools > Options > Text Editor > JavaSCript/TypeScript > Linting > General
deselect "Enable ESLint"

I've run into this as well and was able to return Visual Studio to its normal state by doing the following -
Identify the project where the red lined code comes from
Remove the "red line" project from the references where it is being used (ProjectName\References - right click, add references, and uncheck the "red line" project)
Build (you should get errors now)
Readd the project reference that was just removed
Build again
The red lines should be removed and the project should build!

Steps that work
Open the solution and do a rebuild all
Close the solution
Open solution and do a clean
Close solution
Open solution and do a rebuild all
Close and then open the solution. It should be good. This works for me every time
Be careful deleting some of these settings files as you will lose saved debug settings, etc. And it may do more damage than you realize.

I have found recently it is easy to solve this by switching from Debug to Release in the dropdown to left of the Play Button. Then switching back from Release to Debug.

I had the same problem with lots of red lines in several *cpp source files. Though the code compiled perfectly. None of the other solutions worked for me.
Changing the order of #include lines of a *.cpp-file could make the red lines disappear - and reappear with the restored order.
Then I noticed a header file was included twice in a single *.cpp file. I removed the second one and - everything was fine.
Including a header file twice in the same *.cpp file seems to be no problem to the compiler but to the IntelliSense part.

Simply refresh the project/solution. It will get resolved.

I ran into this problem with the latest Visual Studio 2017.
Also the debug version of my program was running painfully slow.
I deleted the Solution file .sln and created a new one.

I had a similar problem when I was seeing lot of red squiggles in a couple of files. I tried all answers proposed previously, but nothing seemed to work.
The moment I started browsing through the classes, structures in other files for which complaining files had references, the problem disappeared. It seemed IntelliSense was not able to resolve dependencies on its own for some reason.

For me, I had at one time enabled fusion logging to debug some assembly dependency errors (fuslogvw from a CMD prompt). That was months ago and I had been experiencing much slower build times (5-7 minutes) since then.
I had also forgotten entirely that I had left them enabled. These logs were my bottleneck and disabling them has made iterating much faster.

In my case with Visual Studio 2017, I have many "red lines" shown below all symbols defined in a third-party library, but my project can actually build without problems. I have tried all suggested solutions (like delete the .VS folder, restart Visual Studio, etc.), but none of them working.
Finally, I fixed it and this is how: I open my application project's property page, then go to C/C++ → General → Additional Include Directories, which is the place I put all needed third-party library header paths.
I delete all the path (but save them somewhere), click "Ok" to confirm. Then I come back to the same setting, paste those paths back, click "Ok" to confirm, and then all those "red lines" disappear.

I have VS2019 with ReSharper, and ran into this issue.
What worked for me was:
Go to the ReSharper >> Options menu
Go to the General tab (should be the default)
Press the "Clear caches" button
Close all instances of Visual Studio (2019)
Restart Visual Studio

Using VS2022 without Resharper when this problem occurred, tried several things, this did help me in the end:
Close Visual Studio
Delete folder .vs in the Solution folder
Go to folder %USERPROFILE%\AppData\Roaming\Microsoft\VisualStudio\
Delete all folders whose names start with 17.
Reopen Visual Studio
More specific subfolders could exist that might be enough to delete, but I had no issues after deleting all of it. AFAIK these only contains user session data, temporary files and/or cache files that can be downloaded again or recreated as needed.

Found this solution:
Close Visual Studio (ensure devenv.exe is not present in the Task Manager).
Delete the %USERPROFILE%\AppData\Local\Microsoft\VisualStudio\xx\ComponentModelCache directory.
Restart Visual Studio.

I have had this problem for months and have finally fixed it. Closing Visual Studio and removing the .vs folder located in the solution directory did not work for me.
There was an assemblyIdentity tag in the web.config file which was referencing a library that was not in my references folder. I removed this tag, cleaned, closed and reopened, and the problem was fixed.
Check each of the assemblyIdentity tags in your web.config file and check them against the references folder in solution explorer
Remove any assemblyIdentity tags, including the parent dependentAssembly tag for any which aren't listed in your references folder.
Clean the solution
Close and reopen the solution

Deleting .vs folder did the trick for me.

for me this works:-
Open the Command Palette ctrl+⇧+p
Then type: reload Window.

Deleting all the folders which start with "asp.xxx" worked for me. You can reach these folders by:
(C:\Windows\Microsoft.Net\Framework\vx.xx\Temporary ASP.NET Files)

Hover over the word that has the red underline squibble. A mini dialog box will appear. Click on 'Quick fix' and then click on 'Disable error squibble'.

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.