How can I modify the referenced project DefineConstains before everything? Or any way to change the condition for referenced project?

[Flithor]

I have a C# project that needs to modify the references (including project references and Nuget packages) of the referenced project itself based on some conditions. I tried to use DefineConstains to do this, but after many attempts, I found it may impossible. The referenced project will always complete all reference-related operations before DefineConstains is modified by main project.
Maybe I'm on the wrong way... Is there any solution to implement it?

This is the example reference tree about the solution:
(not only one project D, there are many, and some of "Project D" has referenced by Project A)

Project A (Custom mark "ExcludeC=true")
└ Project B (#if !ExcludeC /*code*/ #endif remove code used NugetPackage C)
　└ NugetPackage C (Condition by "ExcludeC", if true then exclude this package)
Project D
└ Project B
　└ NugetPackage C (No custom mark "ExcludeC", include it)

[KalleOlaviNiemitalo]

Might be doable by adding another project.

Originally:

• A has a ProjectReference on B
• B has a PackageReference on C
• When referenced from A, you want B to have a PackageReference on D instead of C

Change it so that

• A has a ProjectReference on B2
• B2 imports B
• B has a PackageReference on C with Condition="$(MSBuildProjectName) == 'B'"
• B has a PackageReference on D with Condition="$(MSBuildProjectName) == 'B2'"
• B and B2 are in the same directory, so that relative item specs in B refer to the same files even when imported by B2
• B2 sets BaseIntermediateOutPath so that B2 does not use the same obj directory as B

This way NuGet should be able to restore both B and B2 without overwriting files from the other project.

[Flithor]

If there is a way can set all project DefineConstants before everything will be very nice. But looks there is no way...

[Flithor]

I've found a workaround is that check the SolutionName in condition, it can be work for all project.

[GangWang01]

It sounds like project A and project D are not included in the same solution *.sln though they are listed in the same tree described in your question. There are separate solutions including the projects that rely on custom mark ExcludeC=true and the projects that don't respectively. Is it right?

[Flithor]

Project A is referenced by solution X and project D referenced by solution Y, But solution X need exclude package C.
Conditional by solution name is a final workaround for me, because of this workaround will lead to a new "Things to note" in our work management.
If that's a way to condition by project A will be fine.

[GangWang01]

Global property set from the command line may help to avoid using solution name.
It looks like no way to condition by project A.