Visual Studio Does not recognize System.Linq

Question

I created this program and C# and it worked correctly a few weeks ago. Now, I copied all of this code to a another project I am working on. I added it to a brand new C# Class inside of the project I am working on. Visual Studio didn't recognize the assembly references that say "not found" in the comments.

This is just bizarre since they were found in the previous program. Does anyone know why Visual Studio can't find these assembly references.

using System;

using System.Collections.Generic;

using System.Linq;    //not found
using System.Text;
using XML_Creator;     //not found
using System.Xml.Linq; //not found
using System.IO;

Do you have `System.Xml.Linq.dll` referenced in your new project? — Nathan A, Jul 09 '14 at 17:17
@user3670048 The question would be: which target version of the .NET framework is the project using? — Adriano Carneiro, Jul 09 '14 at 17:21
yeah.. you are right.. Target framework.. because it does not work with versions below 3.5. — fabricio, Jul 09 '14 at 17:22

score 19 · Accepted Answer · answered Jul 09 '14 at 17:16

19

An educated guess: It's probably the .NET framework target version of the new project.

System.Linq was introduced on .NET Framework 3.5.

Go to Project -> Properties -> Application and check the Target Framework property. It's probably a target framework prior to 3.5

answered Jul 09 '14 at 17:16

Adriano Carneiro

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This might not actually be the case. My target framework in the project properties was showing 4.0, but I am working in a Web project and the Web.config didn't have a "targetFramework" attribute on the tag. Adding 'targetFramework="4.0"', closing the project, and reopening it fixed it for me. You can also toggle the properties to 3.5 and back to 4.0, but it takes more time. – Daved Nov 05 '15 at 18:41

score 18 · Answer 2 · answered Sep 23 '16 at 02:47

18

You need to add refrence to system.Core.

answered Sep 23 '16 at 02:47

Edwin O.

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Why System.Core.dll rather than System.Linq.dll? – xr280xr Jul 22 '19 at 16:12
@xr280xr If you are still curious, it's because the System.Linq namespace definition is actually in the System.Core assembly (in System.Core.dll). – Joey Jan 06 '20 at 16:24
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In VS2019 (.NET 4.7.X), this reference cannot be (explicitly) added, it fails with "A reference to 'System.Core' could not be added. This component is already automatically referenced by the build system" – LCC Apr 17 '20 at 11:27
Completely new Clean MVC project .net 4.8, gives me this error too. I tried just about everything in here. Coincidentally; if I make a new MVC project in VB, I dont get missing Linq error. Go figure – Christian Mar 10 '21 at 22:19
There are tons of reasons, why one has to stick to .NET framework, instead of Core, typically it's out of his/her hands. In addition to that, you cannot change a .NET framework to Core without quite some work. So even though this might work, it's not very helpful, IMHO. – Oak_3260548 Dec 16 '21 at 06:49

score 10 · Answer 3 · answered Jul 09 '14 at 17:59

10

Step 1) Go to your Project Solution Explorer and Select References
Step 2) Right click it on References and Select Add Reference... a form will appear
Step 3) Search linq on Search bar
Step 4) Now Select/tick the System.XML.Linq checkbox
Step 5) Click Ok

answered Jul 09 '14 at 17:59

Durre

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Somebody already mentioned this...but I when I do this there is no search bar...and I cannot find System.XML.linq – tennis779 Jul 09 '14 at 18:13
7

You need a reference to **System.Core** for **Linq** to work in .Net framework 4 – Durre Jul 09 '14 at 18:27
You just Saved my day – nkigen Apr 02 '17 at 12:19

score 4 · Answer 4 · answered Nov 05 '17 at 08:28

4

If your file is in App_Code folder, try moving it to another folder. For me its solved the problem.

answered Nov 05 '17 at 08:28

Ammar

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score 3 · Answer 5 · answered Jul 09 '14 at 17:24

3

You need to right click on the solution in Solution Explorer and add a reference to System.Xml.Linq and/or System.Linq in Project Properties.

This has hit me several times - I see it a lot with System.Configuration as well. (For some reason those two references seem to be particularly picky)

answered Jul 09 '14 at 17:24

Tim

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Well now I am running into the problem that System.Linq and System.XML.Linq isn't in the browser ... :( – tennis779 Jul 09 '14 at 17:29
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Please note that System.Linq namespace is in the System.Core assembly, not System.Xml.Linq – Adriano Carneiro Jul 09 '14 at 17:31
This did work, I thought I was using the 4.0 framework, when it was set to 2.0... so this didn't show System.XML.Linq – tennis779 Jul 09 '14 at 19:08

Shriram Panchal · Answer 6 · 2015-10-25T01:47:05.263

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For me I tried this and worked:

PROJECT==>Add Reference ==> Browse ==> C:\Windows\winsxs\x86_netfx35linq-system.core_31bf3856ad364e35_6.1.7601.17514_none_6161fc35ed136622\System.core.dll

Or

you can simply find the System.core.dll using windows search on Os System Drive

edited Oct 25 '15 at 01:47

answered Oct 25 '15 at 01:23

Shriram Panchal

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score 0 · Answer 7 · answered Aug 27 '15 at 02:31

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I had a similar issue. I upgraded my asp.net project to .NET Framework 4.5.x and it worked. I did tried 4.5.1 first and then later 4.5.0 and both seem to be helping.

answered Aug 27 '15 at 02:31

Amit

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Visual Studio Does not recognize System.Linq

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