Visual Studio loses ability to attach to Unity, why?

Visual Studio loses ability to attach to Unity, why? - c#

I'm using Visual Studio with Unity. In general in VS I can simply click "Attach to Unity" and it will build the solution and indeed attach to Unity.
Sometimes, however, a project loses the "ability" to do so, what means that suddenly clicking the button will only build the solution and not attach to Unity.
I really would like to know what's happening there as I'm not aware of doing anything that could result in such a behaviour.
There are some parameters that might have an effect:
it happens only for some Unity projects: a project is either "infected" or it happens never (on my watch)
if it starts happening it will always happen until I reboot the PC (closing VS and Unity is not enough)

For me (Unity 2020.x and VS19) this happens quite often.
Simply close VS and in Unity > Edit > Preferences > External Tools
Click on "Regenerate project files" (you don't need to check anything else, just click the button)
Start VS again, and it should work as normal.

For me "Attach to Unity" disappeared from the toolbar.
But I still have a button in Debug -> Attach Unity Debugger
Hope it will help someone.
Visual Studio Community 2019 16.7
Unity 2020.1.2f1

To prevent this from happening:
When there are compiling errors in your code, don't double click on Unity Debug Log line, which opens VS at the line that threw the error, but it messes with the project files.
Regenerating the project files under Unity > Preferences > External Tools > Regenerate Project Files. Also make sure that Visual Studio is set under external tools, as well as all the Unity dependencies are correctly installed via the Visual Studio installer.
Visual Studio will prompt you to reload the project, optionally rebuild your entire solution in VS and restart both Unity and VS.

Delete all visual studio related files from the project folder. sln, csproj, vs (hidden) folder.. Reopen project with unity hub, edit one of script and all files will be generated and you will see Attach to Unity button again.

This is a quite common issue when using Unity. Me and my colleges have experienced this a couple of times each month. It usually automatically "repairs itself" after restarting VS/Unity or in worst case rebooting the computer.
Now, I've got this problem again with latest VS2019. I've tried:
Generate a new clean project
Rebooting
Regenerated all visual studio files
Reinstall VS 2019 (clean)
Reinstall Unity (It is clean - I'm only using one! editor version)
All the above suggestions
Are there any network-related issue to this or how does the attach to Unity works ? Can I check some log-files related to this?
Last time this happened to me, I needed to reinstall Windows. I might be in that situation again.

I had a similar issue, underneath the file tabs does it say miscellaneous files? To fix it I right clicked the Assembly C-Sharp in the solution explorer and rebuilt the project as shown in the picture.

Normally just restarting visual studio is sufficient, this issue was addressed and fixed by MS in VS around early december. Previously it happened each time you made a new script file.
Make sure you have installed the latest visual studio patch, as well as the "visual studio tools for unity"

I had this issue once, what fixed it for me was reconnecting Visual Studio to Unity Edit > Preferences > External Tools > External Script Editor
Also check the correct version of Visual Studio is listed there.

For Unity 2020.1.1 and above
in VisualStudio19:
go to "Build" -> "Rebuild Solution"

Unity > Edit > Preferences > External Tools > Editor Attaching

In my case (Unity 2020.2, VS Code 1.53.2) Attaching Debug option is missing on Unity.
After restarting my macbook,
Open VS Code
Open Unity
In VSCode-> Run -> Start Debugging
Unity show up to me alert just like below.
I choose Enable debugging for all projects option.
I hope, It will help someone.

Related

Unity script has no IntelliSense when opened in visual studio [duplicate]

When I want to edit C# Unity scripts, they open in Visual Studio. It is supposed to provide auto complete for all Unity related code, but it doesn't work.
Here you can see the missing functionality:
As seen, the transform object does not open the autocomplete menu.
Unity version: 5.5.2f1
Visual studio 2015
Visual Studio Tools for Unity is installed

There is no auto-completion because the script says "Miscellaneous Files" instead of the of the name of the Project. Take a look at the image below that came from the video in your question:
The "Miscellaneous Files" message can happen for many reasons:
It can happen when you open your Unity C# file from another folder instead of opening it from Unity Editor.
This can also happen because Unity crashed while Visual Studio is still open therefore corrupting some files.
It can happen because Unity was closed then re-opened but is no longer connected to Visual Studio. When Visual Studio is opened you get "Miscellaneous Files" and no auto-completion.
This can happen when Visual Studio Tools for unity is not installed.
When you create a script from Unity then quickly open it before Unity finish processing it or before the round icon animation stuff finish animating.
Most of the times, restarting Unity and Visual Studio should fix this.
I can't tell which one is causing the problem but I will cover the most likely solution to fix this.
Fix Part 1:
Download and Install Visual Studio Tools for unity from this link. Do this while Unity and Visual Studio are both closed.
From Unity Editor, go to Edit → Preferences... → External Tools. On the External Script Editor drop down menu, change that to Visual Studio 2015.
Fix Part 2:
If newly created C# files are coming up as Miscellaneous then follow the instruction below:
From Visual Studio, go to Tools → Options... → Tools for Unity → Miscellaneous. Under Show connectivity icon, set it to true then restart Visual Studio.
When you re-start, connection icon should now be available in Visual Studio. Click it then choose the Unity instance to connect to. The red 'x' icon should now turn into a brown checkmark icon. Now, when you create a new C# file in Unity, it should open without saying Miscellaneous.
Fix Part 3:
Still not fixed?
Re-import project then open C# Project.
Close Visual Studio.
From Unity, re-import project by going to Assets → Reimport All.
Now, open the project in Visual Studio by going to Assets → Open C# Project. This will reload the project and fix possible solution file problems.
Fix Part 4:
Still not fixed?
Fix each C# file individually.
Click on Show All Files icon.
Select the script that doesn't do auto-complete then right-click and select Include In Project.
Fix Part 5:
Not fixed yet?
Credit goes to chrisvarnz for this particular solution which seems to have worked for multiple people.
Close Visual Studio
Go your project directory and delete all the generated Visual Studio files.
These are the files extensions to delete:
.csproj
.user
.sln
Example:
Let's say that the name of your Project is called Target_Shoot, these are what the files to delete should look like:
Target_Shoot.csproj
Target_Shoot.Editor.csproj
Target_Shoot.Editor.csproj.user
Target_Shoot.Player.csproj
Target_Shoot.Player.csproj.user
Target_Shoot.sln
Do not delete anything else.
Double click on the script again from Unity which should generate new Visual Studio file then open Visual Studio. This may solve your problem.
Fix Part 6:
If not working, check if you are having this error:
The "GetReferenceNearestTargetFrameworkTask" task was not found
Install Nuget PackageManager from here.
Restart Visual Studio.
See this answer for more information.
Fix Part 7
Make sure all of the projects are loaded.
In Solution Explorer it should tell you # of # projects.
If all of the projects are not showing, right click on "Solution (# of # projects)" and click Load Projects.

Try this,
In Unity Editor Go to Menu, Click on Edit -> Preferences -> External Tools -> External Script Editor. Set it to Visual Studio (your installed version of VS).
Now in Menubar go to Edit -> Project Settings -> Player Settings -> Other Settings -> Under Configuration -> Check API Compatibility Level -> Change it to your installed .Net version. In my case I set it to .Net 4.x
Now if Visual Studio is running already go to Visual Studio, it will ask to reload project. Reload the project. Check if it works, if not close Visual Studio. Now Open cs file from Unity Editor, and now it should work.

I found another way to fix this issue in a more convenient manner:
Select the broken file in Solution Explorer.
Open its Properties.
Switch field "Build Action" from "Compile" to "None".
Then switch it back to "Compile".
This will kill the synchronization between Unity and Visual Studio somehow.
The next time Visual Studio will reload the project, it will prompt a warning.
Just click on "Discard".

If you have done all of the above and still isn't working , just try this:
Note: you should have updated VS.
Goto Unity > edit> preference >External tools> external script editor.
Somehow for me I had not selected "visual studio" for external script editor and it was not working. As soon as i selected this and doubled clicked on c# file from unity it started working.
I hope it helps you too.

Unload and reload the project, in Visual Studio:
right click your project in Solution Explorer
select Unload Project
select Reload Project
Fixed!
I found this solution to work the best (easiest), having run into the problem multiple times.
Source: https://alexdunn.org/2017/04/26/xamarin-tips-fixing-the-highlighting-drop-in-your-xamarin-android-projects/

This page helped me fix the issue.
Fix for Unity disconnected from Visual Studio
In the Unity Editor, select the Edit > Preferences menu.
Select the External Tools tab on the left.
For External Script Editor, Choose the Visual Studio version you have.
Click regenerate Files
You Done

Select project in Visual Studio
Click "Refresh" button

I hit the same issues today using Visual Studio 2017 15.4.5 with Unity 2017.
I was able to fix the issue by right clicking on the project in Visual Studio and changing the target framework from 3.5 to 4.5.
Hope this helps anyone else in a similar scenario.

Two Alternative Options:
Fix 1
#singleton pointed me in this direction. Instead of changing the target in Visual Studio you should change it in Unity since the project is auto-generated.
First delete the auto generated Visual Studio files:
.csproj
.user
.sln
Then from within Unity go to PlayerSettings and under 'Other Settings' change the 'Scripting Runtime Version' from Stable 3.5 to Experimental 4.6.
However, that didn't fix it for me.
Fix 2
I noticed all of the references to Unity related code was marked with a yellow warning. Check your error logs and see if this is the case. In particular see if you get the following error: getreferenceNearestTargetframeworkTask
If so try:
Start Visual Studio Installer again.
On the Build Tools 2017, click Modify,
Ensure that "Nuget targets and build tasks" are ticked. This should become ticked if you click on Universal Windows Platform development.

Update 2020 with Visual Studio Community 2019 and Unity 2019.3:
Open Visual Studio Installer as Administrator, select to modify your current installation and add "Game development for Unity"
If you add a new c# script in Unity now, and open it (automatically) with Visual Studio, it is not described as "Miscellaneous" at the top of the window but with "Assembly-CSharp", and the autocomplete works.

i found my solution by creating the .cs file from visual studio itself instead of unity editor
right click on project folder in solution explorer
add > new item
type "unity" on the search field on the top right
select "CSharp MonoBehaviour"
name your script on the bottom and click Add

In my case, correct .net version was not installed on my PC. I install the .net 3.5 on my pc and that worked for me.

For Windows or macOS:
Download/Install the Visual Studio IDE (with Unity Tools)
When installing, make sure you include installation of
Game development with Unity
Then using Unity (you can double click one of your C# files), open a new C# project and the Visual Studio IDE should open with your new project structure.
From there, you should be able to see what you are looking for.
For example:
For Linux (suggestion):
Try Monodevelop - Additional Information, it provides code completion/hints.

My autocomplete also didn't work because Visual Studio Tools for Unity wasn't installed. So, after you install that, delete the auto generated Visual Studio files. Others said that you open file again and the problem is solved but it's not.
The trick is: instead of normally double-clicking the file, you need to open the C# file from Unity by right click and then "Open C# Project".

The issue I faced was that the C# Project was targeting a different .NET Framework (4.7.2), whereas the Unity project had a different target (.NET 3.5).
I fixed this by changing the target in Unity as-
File -> Build Settings -> Player Settings -> Other Settings -> API
Compatibility Level : Set it to the .NET version you already have
installed (Check your .NET Version here). In my case, it was 4.x
After this, Visual Studio worked perfectly and autocorrect was fixed too.

Try pressing Ctrl + Alt + Space (which toggles between suggestion and standard completion modes)

For some odd reason, the "Game development with Unity" tool can become disabled in Visual Studio.
To fix this..
Open Visual Studio
Go to Extensions → "Manage Extensions" → Installed
Find "Visual Studio 2019 Tools for Unity"
If it is disabled, enable it
Restart VS
Credit to Yuli Levtov's answer on another Thread

The following works for me.
Go to Edit->Preferences->External Tools->External Script Editor Select Scripting Editor

I solved to install the same version of .NET on WIN that was configured in my Unity project. (Player Settings)

Go to Options on the Tools menu and then select Documents in the Environment node. (If Documents does not appear in the list, select Show all settings in the Options dialog box.)
Put a tick on "Miscellaneous files in Solution Explorer" and Click OK. (This option displays the "Miscellaneous Files" node in Solution Explorer. Miscellaneous files are files that are not associated with a project or solution but can appear in Solution Explorer for your convenience if you tick this option.)
Locate your file in the Solution Explorer under "Miscellaneous Files". Then drag and drop your file to where it should belong and voila! This will copy the file to where you drop it. You may now safely delete the older file under Miscellaneous Files folder if you wish to do so
Credits: https://stackoverflow.com/a/47662523/10471480
In case Scripts folder is not visible:
Click on "Show all files" in Solution Explorer
Locate the Scripts folder.
Right Click on Scripts and select "Include in Project"

Keep in mind that if you are using the ReSharper tool, it will override the IntelliSense and show it's own. To change that, on VS, go to Extensions -> ReSharper -> Options -> IntelliSense -> General then choose Visual Studio and not ReSharper.

Before restarting and/or re-installing VS, First try opening any other of your projects to see if Intellisence works, if it does, then issue probably lies with your current project. First, most probable victim would be the NUGET packages with pending updates. To Fix this,
Right click on references
Proceed to Manage NUGET Packages Under NUGET Packages
proceed to updates Install Updates and recheck Intellisence

I tried all of these but ended up finding out that I needed to right-click the solution in Solution Explorer and add existing items and find the C# assembly file in Window's Explorer. There seem to be a bazillion different problems that give you this error, this is likely the most simple solution. If you double click on your script from unity, it does not seem to drag the assembly along.

Another possible fix:
In the project window, click on the Assets folder
Right click, and Create -> C# Script
Double click that, and wait.
For some reason, this work.

None of the above solutions worked for me. However I opened the ProjectName.CSPROJ file and manually added the new file and it worked like charm

What worked me is that I copied all the code inside the broken class and removed that file.
Then, I opened an empty file with the same name and pasted back.
Result: beautiful syntax highlights came back!

"Preferences" -> "External tools" -> set you exteranl tool
Thats one fix. Also for VS you can use ReSharper by JetBrains, but I recommend use Rider. That one is also free for students.
It provides less performance than visual studio, but more than VS+Resharper definitely.
Have a good day, mate)

Try with combination: Ctrl + Alt + Space

one of the above methods are worked for me and I just found a solution to this problem,
1. First, go to the project directory and delete .sln file
2. Second, go to unity and double click your script. Then Visual Studio will be open with an error,
Then click ok and close Visual Studio editor.
Finally, turn off your Windows Defender and then go to your project directory and there will be .csproj file. Just double click and open this from your Visual Studio editor and open the scripts folder inside the assets folder and open the scripts and autocompletion will be working perfectly fine.

These actions solved the problem for my projects in Visual Studio 2022
FIX 1
Solution
Assembly-CSharp (right-click)
Load Entire Dependency Tree
FIX 2
Solution
Assembly-CSharp
References
Double click on any lib to force loading

Visual Studio doesn't autocomplete or show suggestions on unity external dll [duplicate]

When I want to edit C# Unity scripts, they open in Visual Studio. It is supposed to provide auto complete for all Unity related code, but it doesn't work.
Here you can see the missing functionality:
As seen, the transform object does not open the autocomplete menu.
Unity version: 5.5.2f1
Visual studio 2015
Visual Studio Tools for Unity is installed

Try this,
In Unity Editor Go to Menu, Click on Edit -> Preferences -> External Tools -> External Script Editor. Set it to Visual Studio (your installed version of VS).
Now in Menubar go to Edit -> Project Settings -> Player Settings -> Other Settings -> Under Configuration -> Check API Compatibility Level -> Change it to your installed .Net version. In my case I set it to .Net 4.x
Now if Visual Studio is running already go to Visual Studio, it will ask to reload project. Reload the project. Check if it works, if not close Visual Studio. Now Open cs file from Unity Editor, and now it should work.

I found another way to fix this issue in a more convenient manner:
Select the broken file in Solution Explorer.
Open its Properties.
Switch field "Build Action" from "Compile" to "None".
Then switch it back to "Compile".
This will kill the synchronization between Unity and Visual Studio somehow.
The next time Visual Studio will reload the project, it will prompt a warning.
Just click on "Discard".

If you have done all of the above and still isn't working , just try this:
Note: you should have updated VS.
Goto Unity > edit> preference >External tools> external script editor.
Somehow for me I had not selected "visual studio" for external script editor and it was not working. As soon as i selected this and doubled clicked on c# file from unity it started working.
I hope it helps you too.

Unload and reload the project, in Visual Studio:
right click your project in Solution Explorer
select Unload Project
select Reload Project
Fixed!
I found this solution to work the best (easiest), having run into the problem multiple times.
Source: https://alexdunn.org/2017/04/26/xamarin-tips-fixing-the-highlighting-drop-in-your-xamarin-android-projects/

This page helped me fix the issue.
Fix for Unity disconnected from Visual Studio
In the Unity Editor, select the Edit > Preferences menu.
Select the External Tools tab on the left.
For External Script Editor, Choose the Visual Studio version you have.
Click regenerate Files
You Done

Select project in Visual Studio
Click "Refresh" button

I hit the same issues today using Visual Studio 2017 15.4.5 with Unity 2017.
I was able to fix the issue by right clicking on the project in Visual Studio and changing the target framework from 3.5 to 4.5.
Hope this helps anyone else in a similar scenario.

Two Alternative Options:
Fix 1
#singleton pointed me in this direction. Instead of changing the target in Visual Studio you should change it in Unity since the project is auto-generated.
First delete the auto generated Visual Studio files:
.csproj
.user
.sln
Then from within Unity go to PlayerSettings and under 'Other Settings' change the 'Scripting Runtime Version' from Stable 3.5 to Experimental 4.6.
However, that didn't fix it for me.
Fix 2
I noticed all of the references to Unity related code was marked with a yellow warning. Check your error logs and see if this is the case. In particular see if you get the following error: getreferenceNearestTargetframeworkTask
If so try:
Start Visual Studio Installer again.
On the Build Tools 2017, click Modify,
Ensure that "Nuget targets and build tasks" are ticked. This should become ticked if you click on Universal Windows Platform development.

Update 2020 with Visual Studio Community 2019 and Unity 2019.3:
Open Visual Studio Installer as Administrator, select to modify your current installation and add "Game development for Unity"
If you add a new c# script in Unity now, and open it (automatically) with Visual Studio, it is not described as "Miscellaneous" at the top of the window but with "Assembly-CSharp", and the autocomplete works.

i found my solution by creating the .cs file from visual studio itself instead of unity editor
right click on project folder in solution explorer
add > new item
type "unity" on the search field on the top right
select "CSharp MonoBehaviour"
name your script on the bottom and click Add

In my case, correct .net version was not installed on my PC. I install the .net 3.5 on my pc and that worked for me.

For Windows or macOS:
Download/Install the Visual Studio IDE (with Unity Tools)
When installing, make sure you include installation of
Game development with Unity
Then using Unity (you can double click one of your C# files), open a new C# project and the Visual Studio IDE should open with your new project structure.
From there, you should be able to see what you are looking for.
For example:
For Linux (suggestion):
Try Monodevelop - Additional Information, it provides code completion/hints.

My autocomplete also didn't work because Visual Studio Tools for Unity wasn't installed. So, after you install that, delete the auto generated Visual Studio files. Others said that you open file again and the problem is solved but it's not.
The trick is: instead of normally double-clicking the file, you need to open the C# file from Unity by right click and then "Open C# Project".

The issue I faced was that the C# Project was targeting a different .NET Framework (4.7.2), whereas the Unity project had a different target (.NET 3.5).
I fixed this by changing the target in Unity as-
File -> Build Settings -> Player Settings -> Other Settings -> API
Compatibility Level : Set it to the .NET version you already have
installed (Check your .NET Version here). In my case, it was 4.x
After this, Visual Studio worked perfectly and autocorrect was fixed too.

Try pressing Ctrl + Alt + Space (which toggles between suggestion and standard completion modes)

For some odd reason, the "Game development with Unity" tool can become disabled in Visual Studio.
To fix this..
Open Visual Studio
Go to Extensions → "Manage Extensions" → Installed
Find "Visual Studio 2019 Tools for Unity"
If it is disabled, enable it
Restart VS
Credit to Yuli Levtov's answer on another Thread

The following works for me.
Go to Edit->Preferences->External Tools->External Script Editor Select Scripting Editor

I solved to install the same version of .NET on WIN that was configured in my Unity project. (Player Settings)

Go to Options on the Tools menu and then select Documents in the Environment node. (If Documents does not appear in the list, select Show all settings in the Options dialog box.)
Put a tick on "Miscellaneous files in Solution Explorer" and Click OK. (This option displays the "Miscellaneous Files" node in Solution Explorer. Miscellaneous files are files that are not associated with a project or solution but can appear in Solution Explorer for your convenience if you tick this option.)
Locate your file in the Solution Explorer under "Miscellaneous Files". Then drag and drop your file to where it should belong and voila! This will copy the file to where you drop it. You may now safely delete the older file under Miscellaneous Files folder if you wish to do so
Credits: https://stackoverflow.com/a/47662523/10471480
In case Scripts folder is not visible:
Click on "Show all files" in Solution Explorer
Locate the Scripts folder.
Right Click on Scripts and select "Include in Project"

Keep in mind that if you are using the ReSharper tool, it will override the IntelliSense and show it's own. To change that, on VS, go to Extensions -> ReSharper -> Options -> IntelliSense -> General then choose Visual Studio and not ReSharper.

Before restarting and/or re-installing VS, First try opening any other of your projects to see if Intellisence works, if it does, then issue probably lies with your current project. First, most probable victim would be the NUGET packages with pending updates. To Fix this,
Right click on references
Proceed to Manage NUGET Packages Under NUGET Packages
proceed to updates Install Updates and recheck Intellisence

I tried all of these but ended up finding out that I needed to right-click the solution in Solution Explorer and add existing items and find the C# assembly file in Window's Explorer. There seem to be a bazillion different problems that give you this error, this is likely the most simple solution. If you double click on your script from unity, it does not seem to drag the assembly along.

Another possible fix:
In the project window, click on the Assets folder
Right click, and Create -> C# Script
Double click that, and wait.
For some reason, this work.

None of the above solutions worked for me. However I opened the ProjectName.CSPROJ file and manually added the new file and it worked like charm

What worked me is that I copied all the code inside the broken class and removed that file.
Then, I opened an empty file with the same name and pasted back.
Result: beautiful syntax highlights came back!

"Preferences" -> "External tools" -> set you exteranl tool
Thats one fix. Also for VS you can use ReSharper by JetBrains, but I recommend use Rider. That one is also free for students.
It provides less performance than visual studio, but more than VS+Resharper definitely.
Have a good day, mate)

Try with combination: Ctrl + Alt + Space

one of the above methods are worked for me and I just found a solution to this problem,
1. First, go to the project directory and delete .sln file
2. Second, go to unity and double click your script. Then Visual Studio will be open with an error,
Then click ok and close Visual Studio editor.
Finally, turn off your Windows Defender and then go to your project directory and there will be .csproj file. Just double click and open this from your Visual Studio editor and open the scripts folder inside the assets folder and open the scripts and autocompletion will be working perfectly fine.

These actions solved the problem for my projects in Visual Studio 2022
FIX 1
Solution
Assembly-CSharp (right-click)
Load Entire Dependency Tree
FIX 2
Solution
Assembly-CSharp
References
Double click on any lib to force loading

Visual Studio Community 2015 - Unity IntelliSense not showing [duplicate]

When I want to edit C# Unity scripts, they open in Visual Studio. It is supposed to provide auto complete for all Unity related code, but it doesn't work.
Here you can see the missing functionality:
As seen, the transform object does not open the autocomplete menu.
Unity version: 5.5.2f1
Visual studio 2015
Visual Studio Tools for Unity is installed

Try this,
In Unity Editor Go to Menu, Click on Edit -> Preferences -> External Tools -> External Script Editor. Set it to Visual Studio (your installed version of VS).
Now in Menubar go to Edit -> Project Settings -> Player Settings -> Other Settings -> Under Configuration -> Check API Compatibility Level -> Change it to your installed .Net version. In my case I set it to .Net 4.x
Now if Visual Studio is running already go to Visual Studio, it will ask to reload project. Reload the project. Check if it works, if not close Visual Studio. Now Open cs file from Unity Editor, and now it should work.

I found another way to fix this issue in a more convenient manner:
Select the broken file in Solution Explorer.
Open its Properties.
Switch field "Build Action" from "Compile" to "None".
Then switch it back to "Compile".
This will kill the synchronization between Unity and Visual Studio somehow.
The next time Visual Studio will reload the project, it will prompt a warning.
Just click on "Discard".

If you have done all of the above and still isn't working , just try this:
Note: you should have updated VS.
Goto Unity > edit> preference >External tools> external script editor.
Somehow for me I had not selected "visual studio" for external script editor and it was not working. As soon as i selected this and doubled clicked on c# file from unity it started working.
I hope it helps you too.

Unload and reload the project, in Visual Studio:
right click your project in Solution Explorer
select Unload Project
select Reload Project
Fixed!
I found this solution to work the best (easiest), having run into the problem multiple times.
Source: https://alexdunn.org/2017/04/26/xamarin-tips-fixing-the-highlighting-drop-in-your-xamarin-android-projects/

This page helped me fix the issue.
Fix for Unity disconnected from Visual Studio
In the Unity Editor, select the Edit > Preferences menu.
Select the External Tools tab on the left.
For External Script Editor, Choose the Visual Studio version you have.
Click regenerate Files
You Done

Select project in Visual Studio
Click "Refresh" button

I hit the same issues today using Visual Studio 2017 15.4.5 with Unity 2017.
I was able to fix the issue by right clicking on the project in Visual Studio and changing the target framework from 3.5 to 4.5.
Hope this helps anyone else in a similar scenario.

Two Alternative Options:
Fix 1
#singleton pointed me in this direction. Instead of changing the target in Visual Studio you should change it in Unity since the project is auto-generated.
First delete the auto generated Visual Studio files:
.csproj
.user
.sln
Then from within Unity go to PlayerSettings and under 'Other Settings' change the 'Scripting Runtime Version' from Stable 3.5 to Experimental 4.6.
However, that didn't fix it for me.
Fix 2
I noticed all of the references to Unity related code was marked with a yellow warning. Check your error logs and see if this is the case. In particular see if you get the following error: getreferenceNearestTargetframeworkTask
If so try:
Start Visual Studio Installer again.
On the Build Tools 2017, click Modify,
Ensure that "Nuget targets and build tasks" are ticked. This should become ticked if you click on Universal Windows Platform development.

Update 2020 with Visual Studio Community 2019 and Unity 2019.3:
Open Visual Studio Installer as Administrator, select to modify your current installation and add "Game development for Unity"
If you add a new c# script in Unity now, and open it (automatically) with Visual Studio, it is not described as "Miscellaneous" at the top of the window but with "Assembly-CSharp", and the autocomplete works.

i found my solution by creating the .cs file from visual studio itself instead of unity editor
right click on project folder in solution explorer
add > new item
type "unity" on the search field on the top right
select "CSharp MonoBehaviour"
name your script on the bottom and click Add

In my case, correct .net version was not installed on my PC. I install the .net 3.5 on my pc and that worked for me.

For Windows or macOS:
Download/Install the Visual Studio IDE (with Unity Tools)
When installing, make sure you include installation of
Game development with Unity
Then using Unity (you can double click one of your C# files), open a new C# project and the Visual Studio IDE should open with your new project structure.
From there, you should be able to see what you are looking for.
For example:
For Linux (suggestion):
Try Monodevelop - Additional Information, it provides code completion/hints.

My autocomplete also didn't work because Visual Studio Tools for Unity wasn't installed. So, after you install that, delete the auto generated Visual Studio files. Others said that you open file again and the problem is solved but it's not.
The trick is: instead of normally double-clicking the file, you need to open the C# file from Unity by right click and then "Open C# Project".

The issue I faced was that the C# Project was targeting a different .NET Framework (4.7.2), whereas the Unity project had a different target (.NET 3.5).
I fixed this by changing the target in Unity as-
File -> Build Settings -> Player Settings -> Other Settings -> API
Compatibility Level : Set it to the .NET version you already have
installed (Check your .NET Version here). In my case, it was 4.x
After this, Visual Studio worked perfectly and autocorrect was fixed too.

Try pressing Ctrl + Alt + Space (which toggles between suggestion and standard completion modes)

For some odd reason, the "Game development with Unity" tool can become disabled in Visual Studio.
To fix this..
Open Visual Studio
Go to Extensions → "Manage Extensions" → Installed
Find "Visual Studio 2019 Tools for Unity"
If it is disabled, enable it
Restart VS
Credit to Yuli Levtov's answer on another Thread

The following works for me.
Go to Edit->Preferences->External Tools->External Script Editor Select Scripting Editor

I solved to install the same version of .NET on WIN that was configured in my Unity project. (Player Settings)

Go to Options on the Tools menu and then select Documents in the Environment node. (If Documents does not appear in the list, select Show all settings in the Options dialog box.)
Put a tick on "Miscellaneous files in Solution Explorer" and Click OK. (This option displays the "Miscellaneous Files" node in Solution Explorer. Miscellaneous files are files that are not associated with a project or solution but can appear in Solution Explorer for your convenience if you tick this option.)
Locate your file in the Solution Explorer under "Miscellaneous Files". Then drag and drop your file to where it should belong and voila! This will copy the file to where you drop it. You may now safely delete the older file under Miscellaneous Files folder if you wish to do so
Credits: https://stackoverflow.com/a/47662523/10471480
In case Scripts folder is not visible:
Click on "Show all files" in Solution Explorer
Locate the Scripts folder.
Right Click on Scripts and select "Include in Project"

Keep in mind that if you are using the ReSharper tool, it will override the IntelliSense and show it's own. To change that, on VS, go to Extensions -> ReSharper -> Options -> IntelliSense -> General then choose Visual Studio and not ReSharper.

Before restarting and/or re-installing VS, First try opening any other of your projects to see if Intellisence works, if it does, then issue probably lies with your current project. First, most probable victim would be the NUGET packages with pending updates. To Fix this,
Right click on references
Proceed to Manage NUGET Packages Under NUGET Packages
proceed to updates Install Updates and recheck Intellisence

I tried all of these but ended up finding out that I needed to right-click the solution in Solution Explorer and add existing items and find the C# assembly file in Window's Explorer. There seem to be a bazillion different problems that give you this error, this is likely the most simple solution. If you double click on your script from unity, it does not seem to drag the assembly along.

Another possible fix:
In the project window, click on the Assets folder
Right click, and Create -> C# Script
Double click that, and wait.
For some reason, this work.

None of the above solutions worked for me. However I opened the ProjectName.CSPROJ file and manually added the new file and it worked like charm

What worked me is that I copied all the code inside the broken class and removed that file.
Then, I opened an empty file with the same name and pasted back.
Result: beautiful syntax highlights came back!

"Preferences" -> "External tools" -> set you exteranl tool
Thats one fix. Also for VS you can use ReSharper by JetBrains, but I recommend use Rider. That one is also free for students.
It provides less performance than visual studio, but more than VS+Resharper definitely.
Have a good day, mate)

Try with combination: Ctrl + Alt + Space

one of the above methods are worked for me and I just found a solution to this problem,
1. First, go to the project directory and delete .sln file
2. Second, go to unity and double click your script. Then Visual Studio will be open with an error,
Then click ok and close Visual Studio editor.
Finally, turn off your Windows Defender and then go to your project directory and there will be .csproj file. Just double click and open this from your Visual Studio editor and open the scripts folder inside the assets folder and open the scripts and autocompletion will be working perfectly fine.

These actions solved the problem for my projects in Visual Studio 2022
FIX 1
Solution
Assembly-CSharp (right-click)
Load Entire Dependency Tree
FIX 2
Solution
Assembly-CSharp
References
Double click on any lib to force loading

Unity Scripts edited in Visual studio don't provide autocomplete

When I want to edit C# Unity scripts, they open in Visual Studio. It is supposed to provide auto complete for all Unity related code, but it doesn't work.
Here you can see the missing functionality:
As seen, the transform object does not open the autocomplete menu.
Unity version: 5.5.2f1
Visual studio 2015
Visual Studio Tools for Unity is installed

Try this,
In Unity Editor Go to Menu, Click on Edit -> Preferences -> External Tools -> External Script Editor. Set it to Visual Studio (your installed version of VS).
Now in Menubar go to Edit -> Project Settings -> Player Settings -> Other Settings -> Under Configuration -> Check API Compatibility Level -> Change it to your installed .Net version. In my case I set it to .Net 4.x
Now if Visual Studio is running already go to Visual Studio, it will ask to reload project. Reload the project. Check if it works, if not close Visual Studio. Now Open cs file from Unity Editor, and now it should work.

I found another way to fix this issue in a more convenient manner:
Select the broken file in Solution Explorer.
Open its Properties.
Switch field "Build Action" from "Compile" to "None".
Then switch it back to "Compile".
This will kill the synchronization between Unity and Visual Studio somehow.
The next time Visual Studio will reload the project, it will prompt a warning.
Just click on "Discard".

If you have done all of the above and still isn't working , just try this:
Note: you should have updated VS.
Goto Unity > edit> preference >External tools> external script editor.
Somehow for me I had not selected "visual studio" for external script editor and it was not working. As soon as i selected this and doubled clicked on c# file from unity it started working.
I hope it helps you too.

Unload and reload the project, in Visual Studio:
right click your project in Solution Explorer
select Unload Project
select Reload Project
Fixed!
I found this solution to work the best (easiest), having run into the problem multiple times.
Source: https://alexdunn.org/2017/04/26/xamarin-tips-fixing-the-highlighting-drop-in-your-xamarin-android-projects/

This page helped me fix the issue.
Fix for Unity disconnected from Visual Studio
In the Unity Editor, select the Edit > Preferences menu.
Select the External Tools tab on the left.
For External Script Editor, Choose the Visual Studio version you have.
Click regenerate Files
You Done

Select project in Visual Studio
Click "Refresh" button

I hit the same issues today using Visual Studio 2017 15.4.5 with Unity 2017.
I was able to fix the issue by right clicking on the project in Visual Studio and changing the target framework from 3.5 to 4.5.
Hope this helps anyone else in a similar scenario.

Two Alternative Options:
Fix 1
#singleton pointed me in this direction. Instead of changing the target in Visual Studio you should change it in Unity since the project is auto-generated.
First delete the auto generated Visual Studio files:
.csproj
.user
.sln
Then from within Unity go to PlayerSettings and under 'Other Settings' change the 'Scripting Runtime Version' from Stable 3.5 to Experimental 4.6.
However, that didn't fix it for me.
Fix 2
I noticed all of the references to Unity related code was marked with a yellow warning. Check your error logs and see if this is the case. In particular see if you get the following error: getreferenceNearestTargetframeworkTask
If so try:
Start Visual Studio Installer again.
On the Build Tools 2017, click Modify,
Ensure that "Nuget targets and build tasks" are ticked. This should become ticked if you click on Universal Windows Platform development.

Update 2020 with Visual Studio Community 2019 and Unity 2019.3:
Open Visual Studio Installer as Administrator, select to modify your current installation and add "Game development for Unity"
If you add a new c# script in Unity now, and open it (automatically) with Visual Studio, it is not described as "Miscellaneous" at the top of the window but with "Assembly-CSharp", and the autocomplete works.

i found my solution by creating the .cs file from visual studio itself instead of unity editor
right click on project folder in solution explorer
add > new item
type "unity" on the search field on the top right
select "CSharp MonoBehaviour"
name your script on the bottom and click Add

In my case, correct .net version was not installed on my PC. I install the .net 3.5 on my pc and that worked for me.

For Windows or macOS:
Download/Install the Visual Studio IDE (with Unity Tools)
When installing, make sure you include installation of
Game development with Unity
Then using Unity (you can double click one of your C# files), open a new C# project and the Visual Studio IDE should open with your new project structure.
From there, you should be able to see what you are looking for.
For example:
For Linux (suggestion):
Try Monodevelop - Additional Information, it provides code completion/hints.

My autocomplete also didn't work because Visual Studio Tools for Unity wasn't installed. So, after you install that, delete the auto generated Visual Studio files. Others said that you open file again and the problem is solved but it's not.
The trick is: instead of normally double-clicking the file, you need to open the C# file from Unity by right click and then "Open C# Project".

The issue I faced was that the C# Project was targeting a different .NET Framework (4.7.2), whereas the Unity project had a different target (.NET 3.5).
I fixed this by changing the target in Unity as-
File -> Build Settings -> Player Settings -> Other Settings -> API
Compatibility Level : Set it to the .NET version you already have
installed (Check your .NET Version here). In my case, it was 4.x
After this, Visual Studio worked perfectly and autocorrect was fixed too.

Try pressing Ctrl + Alt + Space (which toggles between suggestion and standard completion modes)

For some odd reason, the "Game development with Unity" tool can become disabled in Visual Studio.
To fix this..
Open Visual Studio
Go to Extensions → "Manage Extensions" → Installed
Find "Visual Studio 2019 Tools for Unity"
If it is disabled, enable it
Restart VS
Credit to Yuli Levtov's answer on another Thread

The following works for me.
Go to Edit->Preferences->External Tools->External Script Editor Select Scripting Editor

I solved to install the same version of .NET on WIN that was configured in my Unity project. (Player Settings)

Go to Options on the Tools menu and then select Documents in the Environment node. (If Documents does not appear in the list, select Show all settings in the Options dialog box.)
Put a tick on "Miscellaneous files in Solution Explorer" and Click OK. (This option displays the "Miscellaneous Files" node in Solution Explorer. Miscellaneous files are files that are not associated with a project or solution but can appear in Solution Explorer for your convenience if you tick this option.)
Locate your file in the Solution Explorer under "Miscellaneous Files". Then drag and drop your file to where it should belong and voila! This will copy the file to where you drop it. You may now safely delete the older file under Miscellaneous Files folder if you wish to do so
Credits: https://stackoverflow.com/a/47662523/10471480
In case Scripts folder is not visible:
Click on "Show all files" in Solution Explorer
Locate the Scripts folder.
Right Click on Scripts and select "Include in Project"

Keep in mind that if you are using the ReSharper tool, it will override the IntelliSense and show it's own. To change that, on VS, go to Extensions -> ReSharper -> Options -> IntelliSense -> General then choose Visual Studio and not ReSharper.

Before restarting and/or re-installing VS, First try opening any other of your projects to see if Intellisence works, if it does, then issue probably lies with your current project. First, most probable victim would be the NUGET packages with pending updates. To Fix this,
Right click on references
Proceed to Manage NUGET Packages Under NUGET Packages
proceed to updates Install Updates and recheck Intellisence

I tried all of these but ended up finding out that I needed to right-click the solution in Solution Explorer and add existing items and find the C# assembly file in Window's Explorer. There seem to be a bazillion different problems that give you this error, this is likely the most simple solution. If you double click on your script from unity, it does not seem to drag the assembly along.

Another possible fix:
In the project window, click on the Assets folder
Right click, and Create -> C# Script
Double click that, and wait.
For some reason, this work.

None of the above solutions worked for me. However I opened the ProjectName.CSPROJ file and manually added the new file and it worked like charm

What worked me is that I copied all the code inside the broken class and removed that file.
Then, I opened an empty file with the same name and pasted back.
Result: beautiful syntax highlights came back!

"Preferences" -> "External tools" -> set you exteranl tool
Thats one fix. Also for VS you can use ReSharper by JetBrains, but I recommend use Rider. That one is also free for students.
It provides less performance than visual studio, but more than VS+Resharper definitely.
Have a good day, mate)

Try with combination: Ctrl + Alt + Space

one of the above methods are worked for me and I just found a solution to this problem,
1. First, go to the project directory and delete .sln file
2. Second, go to unity and double click your script. Then Visual Studio will be open with an error,
Then click ok and close Visual Studio editor.
Finally, turn off your Windows Defender and then go to your project directory and there will be .csproj file. Just double click and open this from your Visual Studio editor and open the scripts folder inside the assets folder and open the scripts and autocompletion will be working perfectly fine.

These actions solved the problem for my projects in Visual Studio 2022
FIX 1
Solution
Assembly-CSharp (right-click)
Load Entire Dependency Tree
FIX 2
Solution
Assembly-CSharp
References
Double click on any lib to force loading

VS2015 auto complete function not working

I recently got a new computer but I chose to install VS2015 after reinstalling Unity. I previously used monodevelop but thought I'd give VS a go (partially because it became the default program when opening scripts through Unity and I can't seem to change that).
I am however having a few problems due to the intellisense/auto complete function not working. I've read through a lot of answers on here but nothing seems to help.

My suggestion would be to rebuild your solution files.
From your projects root folder, copy Assets and Project Settings ONLY over to a new directory. From here open up one of your scenes, Unity will import assets and build the scene.
Once open, go to Edit -> Preferences -> External Tools and make sure that Visual Studio 2015 is selected as the External Script Editor and then go Assets -> Sync MonoDevelop Project (Ignore the name MonoDevelop!)
See if that works for you.
Failing that follow the guide here and note what version of Unity you are using as there are different steps for pre 5.2 Getting Started with Visual Studio Tools for Unity
And if that doesn't work, it's going to be a problem with your Visual Studio install. I've had this before even on a new install. So try a re-install as a last resort.

We Keep Coding

C# (C-Sharp) is a programming language developed by Microsoft that runs on the .NET Framework.