I've installed the newly released version of Visual Studio 2017 and started a fresh ASP.NET Core project targeting .NET Core.
Out of the box, I'm getting the
The type or namespace name 'System' could not be found (are you
missing a using directive or an assembly reference?)
error. Any idea what's causing this and how to fix it?
Also, looks like there are problems with NuGet packages as well:
I also tried dotnet restore on the project through the command line and got the following error:
P.S. Kind of disheartening that you get an error in a fresh new project in the latest version of Visual Studio 2017!
UPDATE:
SDK version is v 1.0.1 -- see below:
UPDATE 2:
This is very strange. Looks like the original problem was due to NuGet package source pointing to a folder under Visual Studio 2015 folder. I unchecked it and left only nuget.org. With that my project seemed to have restored all the packages and when I started the project it loads up the standard ASP.NET page. But if I open startup.cs file, I get red squigglies all over the place but if I run the project, it works fine. What's going on here?
UPDATE 3:
I closed the project and VS 2017. I then restarted VS 2017 and opened the project and now it seems to be fine. And I'm not referencing the .NETStandard library 1.6.1 and everything seems to be working fine now.
I had the same issue in my Visual studio 2017 .Net Core application. I closed the Visual studio and re-open fixed everything.
Came across the same issue today. I had an old nuget source that no longer existed. So I went into Tools > Nuget Packet Manager and un-checked the wrong one. Hit "Ok", and then rebuilt the project, and it works great now. It seems like you stumbled onto it, but also wanted to verify that it fixed my issue, and it does.
I had the same problem, first when converting a VS2015 net core mvc web project to 2017 and then when trying to create a new core web application in 2017.
Went to Tools|NuGet Package Manager|Package Manager Settings - checked 'Allow NuGet to download missing packages' and 'Automatically check for missing packages during build in VS' and then clicked 'Clear All NuGet Cache(s)'.
Then re-built the solution - it found and loaded all the required packages and ran OK.
May not work for all cases but simple and worth a try.
Multiple closing and reopening of VS2017 fixed it for me.
I had the same issue, the solution for me was to clear the NuGet cache. Tools > NuGet Package Manager > Package Manager Settings > Clear All NuGet Cache(s)
Check the version .NET Command Line Tools in CMD, just type dotnet --info. If version is 1.0.0, then try to install latest version .NET Core SDK from here.
Find the broken project and right click, Unload, right click, Re-load. Fastest fix for me.
If you get the problem while using the CLI, try doing nuget restore instead of dotnet restore as that sometimes pulls down packages that the dotnet CLI seems to miss.
I have had the same issue with Visual Studio 2019 and .NET Core SDK 2.2.
These steps solved the problem:
Close the Visual Studio
Open the Visual Studio as Administrator
Open the Solution
Right click on Solution -> Restore NuGet Packages
I've tried all answers above. For me works only removal and adding the reference again described in the following steps:
Open 'References' under the project.
Right click on 'System' reference.
Click on 'Remove'.
Right click on 'References'.
Click 'Add Reference...'.
From right menu choose an 'Assemblies',
In a search field type 'System'.
Choose 'System' from the list.
Click 'Add' button.
IMPORTANT: Restart the Visual Studio.
'System' reference you can replace with any you need.
Try adding the following line above the other references in the csproj file
<Reference Include="netstandard" />
For me the problem was caused by my project having a custom IntermediateOutputPath. For some reason, if project_name.csproj.nuget.g.targets is not in obj subfolder of project folder, the error occurs.
Using default IntermediateOutputPath or keeping a shadow copy of project_name.csproj.nuget.g.targets in fake obj folder solves the problem for me.
This issue seems to be triggered by a myriad of reasons. Mine was caused by cloning directly from VSTS using Git Bash, my project directory had spaces in it. Git Bash changed those spaces in the path to %20. It was throwing off all the references in my project. So for anyone who tried everything else and are at their wits end, make sure %20 is not in the path.
So, I have cloned the repository from github and started getting this error.
It was my project uploaded from another machine. I later realized that I have used the materialdesign packages in my project.
I have uninstalled and reinstalled these packages and it fixed my issue.
Had the same problem. Uninstalled Application Insights from my projects using the nuget package manager. I'm not looking at that yet, I just wanted core and unit tests. Problem solved.
I also had the same problem.
The is no SDK folder under the Dependencies one. Therefore, no Microsoft.NetCore.App libraries !
To solve this problem, in Nuget manager window, install any nuget which depends on .NetCoreApp (you can install for example Microsoft.AspNetCore or BundlerMinifier.Core from the Microsoft Visual Studio Offline Packages source).
The SDK will be restored by the same time.
Once it is back, you can uninstall the previously added nuget. The SDK will remain in place.
Not quite sure in which order vs 2017 trying to resolve packages.
But my situation was following. In my VS2015 I had configured local and 3rd party source for nuget packages, newly installed version of 2017 loaded them too.
https://api.nuget.org/v3/index.json was first in list.
But vs2017 throwed an error that it can't restore .net core libraries from my another local repo.
After I unchecked all of them except https://api.nuget.org/v3/index.json, it had started to working normally.
I had this problem too, but not right now, this steps solved my problem: Choose Project -> Properties from the menu bar. In the Project properties window, under Configuration Properties -> General, make sure that Common Language Runtime Support is set to Common Language Runtime Support (/clr)
Simply opening the NuGet package manager and then the Visual Studio settings related to it - without changing anything - merely looking around, and when I closed out, the problem was gone.
This seems to be an intermittent issue that can come and go for no obvious reason.
None of the answers here worked for me so I'm posting what did work.
My errors were mostly the same as the original poster but I also had:
Error loading meta data for 'Microsoft.Extensions.FileProviders.Embedded.2.0.1'
hexadecimal value 0x1C invalid character
Every time I attempted to download a different nuget package or restore old packages I would see this error. I also saw the other errors such as:
type or namespace system could not be found
What worked for me:
opened the filepath that the error said the bad metadata was in, which for me was C:\Program Files\dotnet\sdk\NuGetFallbackFolder\microsoft.extensions.fileproviders.embedded\2.0.1
Then, I put the contents of that folder into another folder I named "hiding".
Then, I went back to the nuget package manager and tried to install a package, hoping to have the SDK restored. IOt worked successfully, and all my other errors were gone as well, and the fresh new project runs as it should!
The problem for me occurred when running my Visual Studio as Admin with a separate user-- I had created a Git Repo with the source files in the user documents of my normal account. When I created a new solution in that folder the above errors occurred. Try creating your project in a different place and see if the error still occurs.
I was facing the same issue when I created a new project (.net Core 2.2) in VS2019.In my case there was an Azure package which was creating the problem.I uninstalled it and the project started working fine.
Run mentioned below command to uninstall the package.
Uninstall-Package Microsoft.VisualStudio.Azure.Containers.Tools.Targets -Version 1.7.10
I had the same problem. I cloned a github project and this error came. So I deleted the cloned project and then I cloned the project again and it worked fine.
I have create a sample ASP.NET 5 application (pretty much the example one from New Solution), and pushed it to GIT hosted on Visual Studio Team Services (former Visual Studio Online). I want to set up continuous integration to Azure Web App (former Azure Web Site). I have tried to set it up from Azure portal itself, it did create a new build definition, but it fails to build ASP.NET 5. I have found a guide how to do this, but it never really worked for me, I get errors like this e.g.
Error parsing solution file at C:\a\1\s\Frontend\src\Frontend\Frontend.xproj: Exception has been thrown by the target of an invocation.
Predefined type 'System.Void' is not defined or imported
Another problem is that it seems it really takes a lot of time to install dnvm, get packages, etc. So all in all it's a pain to make it work.
So are there real alternatives for that or more importantly is Microsoft is planning to implement something like a Build ASP.NET 5, Deploy ASP.NET to Azure and such to make it easy as I suppose it's easy with the current ASP.NET 4 apps. I really hope that it will be an option soon since it's quite impossible to work with current build system.
For "System.Void" issue, please check the runtime version in "global.json" file and make sure it is consistent with the dependencies in "project.json" file.
For dnvm install issue, since AspNet5 runtime environment isn't installed on VSTS Hosted Build Agent for now and the different users may use different runtime versions, it requires the user to add a "PreBuild" PowerShell step to read the runtime version in "global.json" file and then install it. If you can make sure that you will always only use one version (For example: 1.0.0-rc1-update1), you can deploy your own build agent and install "1.0.0-rc1-update1" on it, then you can skip the dnvm installation during the build process.
Take a look on http://riffer.eu/wordpress/?p=112. There I have a solution vor asp.net core RC_1.
Amazingly you need only two powershell scripts - there is no compiling / visual studio necessary.
for some reason I am getting an error "cannot read config file" when trying to set the SetExpressCheckout, I have copied across the web config settings, but for some reason I cannot read them, the error isn't very helpful other than what I have mentioned.
I am using mvc4, and to be honest I have had a problem reading the web.config in the past..
any suggestions would be much appreciated.
Just looked at this... thought it might help someone. Looked at the Inner Exception, saw it was looking for the Log4Net dll... so I gave it to the app and hey ho. It worked.
I had a similar problem and ended up getting both the core and merchant sdk source from GitHub. Change the SpecificVersion=True to False for the log4net reference in the core sdk and re-build it. I also re-targeted both for .net 4.0 so I re-built the merchant sdk with a reference to the new core sdk. Import both of these new dll's to your main project and you should be good to go. I had to change the config in 1 place for the section handler.
<section name="paypal" type="PayPal.Manager.SDKConfigHandler, PayPalCoreSDK"/>
since the Assembly name does not have the underscores if built from source (vs downloaded or added via NuGet).
A bit of explanation:
I was already using log4net version 1.11 before adding the sdk. The sdk was looking specifically for version 1.10. these 2 versions have a different public key, so 'simple' binding redirection won't work. If you have a reference to a different version of log4net (for example using ninject logging extensions requires min version 2.11 so these 2 ninject and the paypal sdk, are incompatible off the shelf).
so the root of the problem was actually caused by the dll version issues but manifested as a Configuration exception. check the inner exceptions and see what you get.
ok, just a quick update, I think it must be something to do with MVC, I have created a new empty asp project, copied the sdk config details across, created the same function call as I have in my mvc code, and called it from a simple asp button... and it works ??
does anyone have any ideas why I am getting an error in an mvc4 project, and not in a simple asp project ??
any help or ideas would be much appreciated.
I am trying to get started with the OpenAuth features of MVC4 as described here:
http://pluralsight.com/training/Player?author=scott-allen&name=mvc4-building-m7-security&mode=live&clip=9&course=mvc4-building
I already did start over again a couple of times in order not to miss anything, but even though I am choosing the right template (Internet Application) there is no AuthConfig.cs.
Nor do I find documentation what to do to get the required tasks done manually.
I am pretty sure this is a pretty dumb question, but maybe I don't find the answer because it is so obvious...
thx
I followed these steps:
Open File/New/Project
Select ASP.NET MVC 4 web Application
Then Select internet Application
Once the project was created there should be a AuthConfig.cs file within App_Start folder
unbelievable.. I used the RC Version of Visual Studio and even though I reinstalled MVC4 from scratch the recent version including the openauth extensions wasn't properly available.
Following the same steps on the regular Visual Studio Installation did the trick...
Installation of NServiceBus was smooth and straightforward. No issues there.
Now, I'm trying to play with a sample solution to see what happens behind the screens. Just trying to follow instructions here - http://docs.particular.net/samples/
And I get this error when creating an endpoint.
Reinstalled the VS add-in. Restarted VS 2010. No luck.
Any ideas?
It seems like you don't have the ASP NET MVC 3 project type installed on your environment. Please try installing ASP.Net MVC from http://www.asp.net/mvc/mvc3
If you have tried to install it using the Web Platform Installer Tool, be sure that you installed the right version and product (At least for me, it's easy to pick the wrong one with so many similar named products).