Visual Studio 2008项目组织，用于可执行文件和程序集

Question

I am having a problem setting up the following in Visual Studio 2008: a parent project which includes the entrypoint Main() method class and which declares an interface, and a child project which has classes that implement the interface declared in the parent project.

I have specified that Parent's Output type is a Console application, and Child's Output type is a Class library. In Child I have add a reference to the Parent as a project, and specified that Child depends on Parent and that the build order should be Parent, then Child.

The build succeeds, and as far I can tell, the right things show up in the Child/bin/debug directory: Parent.exe and Child.dll.

However, if I run Parent.exe, then at the point when it should load a class from the Child.dll, it fails with the error message:

exception executing operation System.TypeLoadException: Could not load type 'Child.some.class' from assembly 'Parent, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.

I guess I'm confused as to how to get the Parent and Child projects to play together. I plan on having more child projects that use the same framework that is set up in the Parent, and so I do not want to move the entrypoint class down into the Child project. If I try to specify that the Child project is also a Console application, then the build process fails because there is no Main() entrypoint class in the child (even though the Parent project is included as a reference).

Any help would be welcome! Thanks, Martin

Answer 1

Generally you want to reverse your hierarchy: your .exe project should depend on your satellite assembly projects (what you're calling "Child"). Then, to use the types in your satellite assembly, you want to add a reference from your .exe project to your assembly project. Do this by right-clicking the .exe project in the Solution Explorer of VS, then do Add Reference ... click the Projects tab and choose the assembly project.

Edit: If you want to setup a "framework" for the overall project (either by defining interfaces or base classes) then I'd start by doing so in a single, core assembly; put those definitions in something like MyProject.Core.dll. Then your "implementing" projects / assemblies would have a reference to your MyProject.Core project. With all this said, you maybe looking for something like an IOC / DI framework. See Ninject , StructureMap , Castle Windsor , etc.

Answer 2

You want to avoid circular dependencies.

If you wish to keep the interface and implementasiton separate, then define the interface in a third assembly (class library) that is used by the "child" assembly (class library), then use both the interface and implementation from the application.

Answer 3

So in the fine tradition of answering one's own questions, I worked out that in order to call GetType() successfully, I have to specify the correct assembly. Each project is compiled into its own assembly ( Application.exe , Interface.dll , and Implementation.dll ). So in order to instantiate the implementation class within the Application Main() class, I have to call:

Type actionType = Type.GetType("ImplementationClass", "Implementation", true);

It seems a little hokey, but at least it works.