The type or namespace name 'UI' does not exist in the namespace 'UnityEngine'

[EyeDev44]

The error

Unnecessary using directive. [Assembly-CSharp]csharp(CS8019)
The type or namespace name 'UI' does not exist in the namespace 'UnityEngine' (are you missing an assembly reference?) [Assembly-CSharp]csharp(CS0234)

Appears sometimes after updating project unity version or after reopening project.
I use VSCode. To fix this. I need every time to:

1. Delete .sln in explorer
2. Change default code editor to VS2019
3. Open code from the editor menu with VS
4. Wait untill libraries will be resolved
5. Change editor back
6. Open project code with VSCode.

[isaacnorman]

Did you find any other fix to this? I don’t want to install VS just to prevent this error.

[Kurt-Dekker]

It’s likely the above can simply be accomplished straight from Unity with Assets → Open C# Project. That resolves like 99% of issues quite cleanly, assuming you have your software installed properly.

Here’s my standard blurb for fixing Visual Studio.

This may help you with intellisense and possibly other Visual Studio integration problems:

Sometimes the fix is as simple as doing Assets → Open C# Project from Unity. Other times it requires more.

Intellisense Not Working with Visual Studio (Fix)

Likely, if you have appeared here to this page you are having the problem I had for the past hour or so. Intellisense is not working in Visual Studio. Well lucky for you, I figured out the solution to fix this issue after searching the entire web. So you don’t have to search the web anymore, I will tell you how I fixed the issue. Step 1: Close Visual Studio Step 2: In Unity, go to Edit < Preferences < External Tools (left part of the Window) Step 3: In External Tools go to the part that sa…

Also, try update the VSCode package inside of Unity: Window → Package Manager → Search for Visual Studio Code Editor → Press the Update button

Also, this: No suggestions in Vscode

And here are some more notes:

UnityEngine.UI is now a package:

Where did the UI option in the create menu go?

I get that too. Try either MORE coffee, or LESS coffee. I can never decide which. Meanwhile, at some point in the course of Unity version releases, the UnityEngine.UI module was moved to be a package in the Package Mangler, and this might cause what you are seeing. Go sniff about in the Package Mangler (Window → Package Mangler) and it should be in there. Use caution because there’s a few similarly-named packages. The one you want is just called “Unity UI” [7290742--882043--Screen Shot 202…

Annoying possible issue circa October 2021:

UnityEditor.UI.csproj not found

Hi! I got this one solved but here it is for others <3 In Unity 2020.3.19f with AR project I created a Script and after opening it I got a warning window that said something like "One or more packages were not loaded" and in the output of Visual Studio (2019) there was a message "D:/..directoryPathToProject../UnityEditor.UI.csproj could not be leaded". Based on another post in the forum this should work for Visual Studio Code as well. My solution: In Unity go to Window > Package Manager > …

[isaacnorman]

I just installed VS and followed your steps, but still have the issue.

Edit: this was in reply to the original post.

[isaacnorman]

@Kurt-Dekker

It’s likely the above can simply be accomplished straight from Unity with Assets → Open C# Project. That resolves like 99% of issues quite cleanly, assuming you have your software installed properly.

Here’s my standard blurb for fixing Visual Studio.

This may help you with intellisense and possibly other Visual Studio integration problems:

Sometimes the fix is as simple as doing Assets → Open C# Project from Unity. Other times it requires more.

https://discussions.unity.com/t/778503

Also, try update the VSCode package inside of Unity: Window → Package Manager → Search for Visual Studio Code Editor → Press the Update button

Also, this: https://discussions.unity.com/t/805330/7

And here are some more notes:

UnityEngine.UI is now a package:

https://discussions.unity.com/t/846906/2

Annoying possible issue circa October 2021:

https://discussions.unity.com/t/857386

Thanks for replying.

I’m on latest unity (2021.2.3f1). Latest packages for UI (1.0.0), VS Code. Everything works fine, intellisense etc. The only problem I have is that somehow the reference to UnityEngine.UI isn’t being picked up by VS code somehow. This means I get lots of warnings about any script files that references UI stuff.

I’ve tried reimporting assets in unity. I’ve tried the OP steps to install VS, then regenerate for VS. I’m not familiar with using VS but I could open a script, see now errors and UI code completion seemed fine.

If you google for the issue, there are so many results, so this must be a common problem, I’m just not finding a fix that works.

Maybe I should start a new post with all the details.

[isaacnorman]

I just downgraded the VS Code package (closed unity, edited the manifest.json) - went to 1.1.2 by random. Reloaded unity. Deleted sln and csproj. Then I regenerated proj files in unity (where you pick external editor) and opened vs code. All working fine.

I think there’s a bug in newer versions of the vs code cs proj generation. I’ll see if I can report a bug somewhere…