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Openin unity script in visual studio does not work

I'm having issues to get the latest installment of Unity to work along with it's recommended visual studio 2019. I have a fresh instalation of both of them, done by using the unity hub installer. I create a new project, and make a vanilla c# script and try to open it with visual studio. Visual studio opens, yet there is no project opened, no file shown, not even the project browser pops up.
I have googled a bit and the only recommended sugestion I can find is about making sure that the unity package manager has the Visual Studio package installed which it does have, to the latest version. I don't know what else to do.

I managed to figure out my answer. It seems that what I needed to do was to go into Unity -> Edit -> Preferences -> External tools and select Visual Studio 2019 as my code editor. Then make sure that the Generate csproj file was checked. It seems for some unknown reason that unity does not have this option enabled by default, even though I specified in the Unity Hub installer that I want Visual Studio to be my editor, and I would have expected that all the configurations would have been done automatically.

Unity and VS versions do not match, try changing the VS version (Unity Editor->Edit->Preferences->External Tools->External Script Editor);
Delete the ".vs" folder in the project (this folder is hidden by default, you need to open the hidden files to see it. This folder is boldly deleted, and VS will automatically create it after deletion).
Delete the "Assembly-CSharp.csproj", "Assembly-CSharp-Editor.csproj" and ".sln" files. (Boldly delete, after deleting, VS will automatically create)

Visual studio not giving Hints (intellisense) when i opening the c# scripts through unity,

I recently installed unity ,but I didn't install visual studio with it because I already have installed.
I simply opened unity and I goes to Edit > Preferences > External script editor and I selected Visual studio code . But when I opening my scripts, visual studio not giving hints for my c# code.

You probably need to install the appropriate targeting pack for Unity. That article also has some other helpful extensions to install when developing in Unity.

What you could do is just open it and close it.
What i mean by that is go to Assets > Open C# Project
Once VSCode opened, wait for 1 min, try to write something like Rigidbody.
If intellisense is working it will start giving you hints, if it's still not working
Do the process one more time,
You can refer to these pictures where how VSCode tells you whether Intellisense is working or not.
http://imgur.com/gallery/1YiuPA4

You need to install snippets for Unity in VS code.
Open VS code. Go to Extensions(ctrl+shift+X).
In search field you need to write unity
Then click to Unity Code Snippets and install it in window bellow.
Then you will be able to see Intelesence !

How to get intellisense in Visual Studio Code for Unity functions names?

I am following a tutorial about Unity and I see that the instructor has intellisense when writes the method's name.
However I have only intellisense with classes and variables, I mean Unity classes like Rigidbody and my own variables.
I have also read:
Autocompletion not working in Visual studio
How to enable intellisense in Visual Studio 2017 for Unity

Old question, but I had the same problem just recently.
There must have been an issue in your Assembly-CSharp.csproj or project-name.sln files. Most likely to be the .csproj file. If you take a look at it, you will see various references to .dll files.
You can tell Unity (my version: v2019.2.20f1) to create these for you by enabling Edit > Preferences > Generate all .csproj files.
1. Delete both files.
2. Enable .csproj file generation.
3. Double click on a script in Unity.
This fixed my issue.

I would really like to clear things up a bit for everyone trying to get Intellisense working with Visual Studio Code.
First of all I am writing this for Unity 2019.4.14 (edit: also for 2020.3 and 2021.3).
These are the things you MUST do for this to work:
You need Visual Studio Code (duh)
You need .NET SDK. I don't think it matters which version, latest is the best I guess. Make sure you install the SDK, not the runtime.
Check if you have .NET SDK installed by typing dotnet in the VSCode terminal.
You also need The .NET Framework Dev Pack because otherwise VSCode is going to be throwing this error:
The reference assemblies for .NETFramework,Version=v4.7.1 were not found. To resolve this, install the Developer Pack (SDK/Targeting Pack) for this framework version or retarget your application.
In VSCode search for the 'C# for Visual Studio Code' extension and install it
In Unity go to Package Manager and install Visual Studio Code Editor. This will enable Unity to generate proper project files for VSCode. (might be already installed)
In Unity go to Edit -> Preferences -> External Tools and choose VSCode from the dropdown (could be listed as code.cmd) and after you choose it tick all the checkboxes you want in the Generate .csproj files for section. I checked Embedded Packages, Local Packages, and Packages from unknown sources. Click 'Regenerate project files'
Open any C# file from Unity and you should be good to go. (you might need to restart VSCode after regenerating project files in order for this to work)
Now, what about Unity Code Snippets and Debugger for Unity extensions? Well these are useful helper extensions but they have nothing to do with Intellisense. The first is for quickly typing common Unity patterns and the second is for showing Unity Debug warnings and errors as you type instead of saving and going back to Unity and reading the console.
Hope this was of any help.
p.s.
One more note: Visual Studio Code depends on the solution files we generate through Unity for Intellisense to work. This is important because you have to add the entire project folder to VSCode workspace and not just Assets folder or your Scripts folders. If you add only the Assets folder to VSCode it won't be aware of those solution (.sln) files. If you open scripts through Unity it will probably work regardless.

Although the answer by Alex Myers is helps, its not 100% right. Unity Snippets does give you some snippets, and the illusion of typeahead, it's not actually intellisense.
For true intellisense you need to:
install dotnet on your system (https://code.visualstudio.com/docs/languages/dotnet) and,
install the dotnet extension for VSCode (https://marketplace.visualstudio.com/items?itemName=ms-vscode.csharp)
More information can be found here: https://code.visualstudio.com/docs/languages/dotnet
You can test you have dotnet installed by typing dotnet into the terminal within VSCode.
Note In the image below how I get a full method signature, reference counts, and the yellow hint globe. These are only available when using dotnet + extension (and not available when using the snippets)

Note: my solution does not solve intellisense to function names, but this was the first question that come in fixing intellisense more generally in VSCode.
I needed to update the VSCode package in unity.
In Unity, click Window, then Package Manager, then look for Visual Studio Code Editor. Expand it by pressing triangle, and upgrade to the latest version (for me, it was 1.2.0. I restarted VSCode and it worked.
v1.1.4 had a bug that caused this problem, and was not fixed for about 3 months. It is still the default package installed with a new default project, so you have to change this package version to 1.2.0 in every new project, until they update it.

Check out the guide for Unity Development with VS Code. They recommend a few extensions:
Unity Snippets
Debugger for Unity
Unity Tools
I believe the Unity Snippets extension is what you are looking for.

For anyone having the same problem on a Mac, try setting this value in your .vscode/settings.json (or in the user settings instead of the workspace settings)
"omnisharp.useGlobalMono": "always"

For me just in Unity, Edit/Preferences/External Script Editor, and changed it to My_Install_Location\Microsoft VS Code\Code.exe (maybe hit Regenerate Project Files)

Sorry, I don't have good English, but I'll show you what worked for me.
I opened the C # script in Visual Studio Code and looked for the Assembly-CSharp.csproj file, then, on line 16, I changed the following:
<TargetFrameworkVersion> v4.5 </TargetFrameworkVersion>
For:
<TargetFrameworkVersion> v4.5.1 </TargetFrameworkVersion>
This solved the Intellisense issue.

Intellisense is a pure workflow of .Net Environment. So, you need to have .Net 'Developer pack' (not Runtime) installed on your system as it installs all three necessary components below:
.Net framework
.Net Target pack
.net SDK
reference link: https://dotnet.microsoft.com/download/visual-studio-sdks
It is directly installed to a system admin-accessible path, so no need setting it up. Now, you have to tell VS Code which .Net version to use (whichever you have installed).
Your Unity project will have these two files in the root directory:
Assembly-CSharp.csproj
Assembly-CSharp-Editor.csproj
In these both files search for line (probably 16):
<TargetFrameworkVersion>v4.8</TargetFrameworkVersion>
Edit version that you had just installed (I had 4.8). Then reopen VS Code. Now everything should work fine.

I found another solution since none of the other solutions were working for me and i was searching for hours.(07/08/2021):
I got the feeling i found the solution for a lot of people since i reinstalled windows recently and simply downloaded everything needed to start without other problems.
I got the same error with .NET, .NET Core or .NET Framework, here are some screenshots of the errors:
In the error output, it says to install the Developer Pack for this framework version. You can find the version in the .csproj file:
By installing the .NET Framework of this version on the dotnet microsoft site: .NET Framework download list
i fixed the error after reloading VSCode and got my Intellisense working for Unity.
TLDR:
My fix was too install .NET Framework version 4.7.1

If you still can't enable IntelliSense, make sure you have VS Code opened in the same directory as the .sln file (I had mine opened deeper in the Assets before).
Source:
https://code.visualstudio.com/docs/other/unity

Though the question is 2 years old, the problem pops up occasionally, just like happened to me.
I had the issue myself, so this one is possibly the first that should be checked.
"Install .NET Framework 4.6 Targeting Pack"
WHY?
First of all, I work with dotnet core, not the standard, so I don't have standard libraries installed on my computer. When I started trying Unity, and VS Code with it, this was the missing part I wasn't aware of.
When I hit the issue, I searched the net a while and see this question. Took me another while to notice this framework sentence in "Enabling code completion" section of VS Code and Unity page. So I tried and now I am happy I tried.
Just don't forget you need to restart at least VS Code to get the intellisense working.
PS: Framework version may, and will most possibly, be changed depending on what year we are in, and which versions we use. So if "4.6" is not working then you probably need another version.
PS2: If it is Mac you are looking for, follow the same link above and find the same section I mentioned above to get a link for .NET SDK.

Follow these steps:
Go into your Unity project.
Go to Edit.
Go to Projects preferences.
Go to External tools.
In line "External Script Editor" you have to change to "Visual Studio Cummunity 2019..."
then it should work.

VSCode integration with Unity 2017.1: IntelliSense not able to suggest any type of data

I just heard that Unity will be dropping support on MonoDevelop on its 2018.1 version and went to search for an alternative. VSCode was the best option so I downloaded it and installed all suggested Unity extensions. (https://code.visualstudio.com/docs/other/unity)
I also changed my External Script Editor to Code. I've created a new Unity project for testing. The code snippets are working great for unity methods such as Start () and Update () but whenever I try to declare a variable like:
private Rigidbody rb;
The rigid body is not suggested. I decided to test with other data types, the most essentials like int, float, etc. And none of them are suggested either. What could be happening? Why is IntelliSense not working properly? I've already downloaded the C# extension as suggested at https://code.visualstudio.com/docs/editor/intellisense
I'm on a Mac using MacOS Sierra with the most current version of VSCode and Unity 2017.1.
[EDIT] The problem was solved after I reinstalled, MonoDevelop, VisualStudio for Mac, VSCode and all it's extensions and used mad.meesh suggestion of searching the .sln on project opening. I still don't understand why, but it's working.

Old question, but I had the same problem just recently.
There must have been an issue in your Assembly-CSharp.csproj or project-name.sln files. Most likely to be the .csproj file. If you take a look at it, you will see various references to .dll files.
You can tell Unity (my version: v2019.2.20f1) to create these for you by enabling Edit > Preferences > Generate all .csproj files.
Delete both files.
Enable .csproj file generation.
Double click on a script in Unity.
This fixed my issue.

I followed the tutorial from Microsoft for VS Code with Unity and it seemed to finally do the trick... https://code.visualstudio.com/docs/other/unity
Steps I took:
Installed https://dotnet.microsoft.com/download
Installed https://www.mono-project.com/download/stable/
Installed C# extension in VS Code.
Unity > Preferences (cmd + , on Mac) > External Tools (left toolbar) > External Script Editor > Visual Studio Code.
Then this is the trick I found to work after doing all of this... I open up VS Code prior to starting my Unity Project and manually go into the Unity Project folder and open up everything in VS Code FIRST. Then, with that project already open and working in VS Code with Intellisense, I double click the script in Unity and it will open it up in the already opened VS Code editor and have Intellisense already working! Do my normal workflow for the day and close everything down... then when I start up the next time, just be sure to open the project in VS Code FIRST and then VS Code will recognize it's a C# project and initiate Intellisense and all that jazz.
Hope this helps!

Visual studio code auto-complete

I have just downloaded unity and saw that now it supports Visual studio code, I downloaded it and made it the default editor.
After trying to edit a script, it prompted me to download c# extension and I did, but there is no auto-complete for unity functions. How can I get that? I'm on Mac.
Any help is appreciated.

Maybe too late, but for future comers ...
There is an extension now for visual studio code called MonoBehaviour Snippets by Rachod Petchpho.
Press Ctrl+shift+x in the IDE to open extensions panel then search for MonoBehaviour Snippets, install and reload the IDE, now you will find all the autocomplete for the function names and objects just like MonoDevelop.

I had the same situation and I bang my head to the wall for days. There was no solution on the net as there are few people using Unity on linux with Visual Studio Code. I finally removed mono and went to their site and downloaded the Visual Studio build (even though we use Visual Studio Code). Then volaaa. Auto complete and suggestions related to Unity functions were there. Of course after installing the necessary extensions.
https://www.mono-project.com/download/vs/

I had the same problem with Unity + VS Code combo.
I have found an extension called Unity CodeSnippets
I highly recommend to download it. This is much better than any of other snippets collection for VSCode.

Intellisense (Autocompletion) is a pure workflow of .Net Environment. So, you need to have .Net 'Developer pack' (not Runtime) installed on your system as it installs all three necessary components below:
.Net framework
.Net Target pack
.net SDK
reference link: https://dotnet.microsoft.com/download/visual-studio-sdks
It is directly installed to a system admin-accessible path, so no need setting it up. Now, you have to tell VS Code which .Net version to use (whichever you have installed).
Your Unity project will have these two files in the root directory:
Assembly-CSharp.cs
Assembly-CSharp-Editor.cs
In these both files search for line (probably 16):
<TargetFrameworkVersion>v4.8</TargetFrameworkVersion>
Edit version that you had just installed (I had 4.8). Then reopen VS Code. Now everything should work fine.

You can use the unity integration plugin:
https://code.visualstudio.com/Docs/runtimes/unity
Follow the instructions to get set up. It seems a lot of things to do but I think that's the best one.
If you still hit the issue even by using that plugin then follow this issue at their github page.

https://forum.unity.com/threads/cant-get-vscode-to-work-properly-with-unity.538224/
there are people that found a workaround.
unityoracle user said:
"This issue is that Unity Editor expects the file used to launch VSCode to have a specific name. "
and:
"Specifically, creating a symlink named "code" that opens VSCode fixed this issue"

for me, it works by downloading .NET Framework 4.7.1 Developer Pack
here
here is the link

Follow the steps from https://code.visualstudio.com/docs/other/unity
Then in unity editor, set VS Code as the default Script editor:
Edit -> Preferences -> External Tools -> External Script Editor
Right below, set Embedded packages and Local packages to true

i used these methods and it worked
Change in External Tools: Edit -> Preferences :choose " Visual Studio Code"
Open file : Assembly-CSharp-Editor in your project folder and Download the Framework Version that is the same as the version in this file EX: v4.7.1
Open VScode tool - Settings - >code lens and tick.
source from here:
https://www.gamesmobile.one/2022/01/visual-studio-code-auto-complete-with.html

I installed an older version of c# vscode extension, version 1.16.21, and it is working.