dotnet build not finding Xamarin - xamarin

Question

When running dotnet build in my project, I have the following error:
/path/to/repo/Toolkit/My.Company.Toolkit.Platform.Android/My.Company.Toolkit.Platform.Android.csproj(91,3): error MSB4019: The imported project "/usr/local/share/dotnet/sdk/7.0.102/Xamarin/Android/Xamarin.Android.CSharp.targets" was not found. Confirm that the expression in the Import declaration "/usr/local/share/dotnet/sdk/7.0.102//Xamarin/Android/Xamarin.Android.CSharp.targets" is correct, and that the file exists on disk.
/path/to/repo/Toolkit/My.Company.Toolkit.Platform.iOS/My.Company.Toolkit.Platform.iOS.csproj(195,3): error MSB4019: The imported project "/usr/local/share/dotnet/sdk/7.0.102/Xamarin/iOS/Xamarin.iOS.CSharp.targets" was not found. Confirm that the expression in the Import declaration "/usr/local/share/dotnet/sdk/7.0.102//Xamarin/iOS/Xamarin.iOS.CSharp.targets" is correct, and that the file exists on disk.
I confirm that /usr/local/share/dotnet/sdk/7.0.102/Xamarin/iOS/Xamarin.iOS.CSharp.targets does not exist.
But I don't know how to install it there.
The reference to Xamarin is defined in the csproj like this <Import Project="$(MSBuildExtensionsPath)\Xamarin\Android\Xamarin.Android.CSharp.targets" />.
When I build from Visual Studio I have no issues. And if I try to re-install Xamarin, it says it is already installed.
I am on MacOS.
[UPDATE]
I uninstalled everything (Visual Studio, SDKs/Runtime, dotnet, etc).
Installed just Visual Studio 2022 for Mac.
➜ ~ dotnet --info
.NET SDK:
Version: 7.0.102
Commit: 4bbdd14480
Runtime Environment:
OS Name: Mac OS X
OS Version: 13.1
OS Platform: Darwin
RID: osx.13-arm64
Base Path: /usr/local/share/dotnet/sdk/7.0.102/
Host:
Version: 7.0.2
Architecture: arm64
Commit: d037e070eb
.NET SDKs installed:
6.0.405 [/usr/local/share/dotnet/sdk]
7.0.102 [/usr/local/share/dotnet/sdk]
.NET runtimes installed:
Microsoft.AspNetCore.App 6.0.13 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 7.0.2 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.NETCore.App 6.0.13 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 7.0.2 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Other architectures found:
None
Environment variables:
Not set
global.json file:
Not found
Learn more:
https://aka.ms/dotnet/info
Download .NET:
https://aka.ms/dotnet/download
Now if I try to build the project in the terminal I still have the same error. But if I try to build it from Visual Studio I have a different error.
I have this error in the build output
Target RazorGenerateComponentDeclaration:
/usr/local/share/dotnet/dotnet exec "/Users/redacted/Library/Caches/VisualStudio/17.0/MSBuild/36265_3/Sdks/Microsoft.NET.Sdk.Razor/build/netstandard2.0/../../tools/netcoreapp3.0/rzc.dll" generate
-s
/Users/redacted/Developer/repositories/bcee/Toolkit/MyCompany.Toolkit.Platform.Web/_Imports.razor
-r
_Imports.razor
-o
/Users/redacted/Developer/repositories/bcee/Toolkit/MyCompany.Toolkit.Platform.Web/obj/Debug/netstandard2.1/RazorDeclaration/_Imports.razor.g.cs
-k
component
-p
/Users/redacted/Developer/repositories/bcee/Toolkit/MyCompany.Toolkit.Platform.Web
-t
obj/Debug/netstandard2.1/MyCompany.Toolkit.Platform.Web.RazorComponents.declaration.json
-v
3.0
-c
Default
--root-namespace
MyCompany.Toolkit.Web
--csharp-language-version
8.0
--generate-declaration
The application to execute does not exist: '/Users/redacted/Library/Caches/VisualStudio/17.0/MSBuild/36265_3/Sdks/Microsoft.NET.Sdk.Razor/build/netstandard2.0/../../tools/netcoreapp3.0/rzc.dll'
/Users/redacted/Library/Caches/VisualStudio/17.0/MSBuild/36265_3/Sdks/Microsoft.NET.Sdk.Razor/build/netstandard2.0/Microsoft.NET.Sdk.Razor.Component.targets(106,5): error : rzc generate exited with code 129.
Done building target "RazorGenerateComponentDeclaration" in project "MyCompany.Toolkit.Platform.Web.csproj" -- FAILED.
Done building project "MyCompany.Toolkit.Platform.Web.csproj" -- FAILED.
Build FAILED.
The tools directory does not exists.

Answer 1

At fisrt, you said:
When I build from Visual Studio I have no issues.
The cause should be when you build from the Visual Studio. The framework your project used is .netstandard 2.0. You can check the project.csproj file and the SDK in the /usr/local/share/dotnet/sdk.
In addition, you can check this case which has the similar error as yours. According to it, if the .net version is not compatible with the xamarin will also get this error. dotnet/sdk/7.0.102 should be the .net 7 which is compatible with the .net maui not the xamarin. So you can't use the dotnet build the project.
You can try to find the right value of the MSBuildExtensionsPath and set it in the android and ios .csproj file according to this case which is about set the project's MSBuildExtensionsPath.
Finally, you can try the solution in this case which has the same error message.

Answer 2

The Xamarin tool chain was built upon Mono, so everything you triggered in VS for Mac is kindly processed by MSBuild for Mono (at Mac terminal you can use msbuild --version to learn more).
dotnet build, however, was designed exclusively for .NET Core based projects, so by default it won't be able to handle Xamarin projects, but only .NET MAUI.
As legacy Xamarin projects are going away soon, you should start to migrate to MAUI as soon as you can,
https://dotnet.microsoft.com/en-us/platform/support/policy/xamarin