Hello Dave

Visual Studio does not allow circular dependency. The best practice is to
refactor the app to remove the circular dependency. If you insist on the
demand, one workaround is to use .NET Reflection (see sample 1), the other
one is to use some tricks of csc compiler (see sample 2).

Sample 1 Use .NET Reflection:

1. Add reference "Assembly1.dll" to project Assembly2 in IDE. Then, the
code snippet looks like:
//project Assembly2
namespace Assembly2
{
   public class Class2
   {
       public static string someData1 = "some data 1 in Assembly2.Class2";
       public string someData2 = "some data 2 in Assembly2.Class2";

       public static string SomeMethod1()
       {
           return Assembly1.Class1.someData1;
       }

       public string SomeMethod2()
       {
           Assembly1.Class1 c = new Assembly1.Class1();
           return c.someData2;
       }
   }
}

2. Now, you cannot add reference "Assembly2.dll" to project Assembly1,
which will cause "circular dependency". So, please use reflection to call
the methods of Assembly2 in Assembly1. The code snippet looks like:

namespace Assembly1
{
   public class Class1
   {
       public static string someData1 = "some data 1 in Assembly1.Class1";
       public string someData2 = "some data 2 in Assembly1.Class1";

       public static string SomeMethod1()
       {
           Assembly assembly2 = Assembly.Load("Assembly2");
           Type type = assembly2.GetType("Assembly2.Class2");
           return type.GetField("someData1").GetValue(null) as string;
       }

       public string SomeMethod2()
       {
           Assembly assembly2 = Assembly.Load("Assembly2");
           Type type = assembly2.GetType("Assembly2.Class2");
           object inst = assembly2.CreateInstance("Assembly2.Class2");
           return type.GetField("someData2").GetValue(inst) as string;
       }
   }
}

Sample 2 Use csc.exe to build the app (I do not recommend the trick)

1. Assembly1 and Assembly2  look like:

//project Assembly2
namespace Assembly2
{
   public class Class2
   {
       public static string someData1 = "some data 1 in Assembly2.Class2";
       public string someData2 = "some data 2 in Assembly2.Class2";

       public static string SomeMethod1()
       {
           return Assembly1.Class1.someData1;
       }

       public string SomeMethod2()
       {
           Assembly1.Class1 c = new Assembly1.Class1();
           return c.someData2;
       }
   }
}

namespace Assembly1
{
   public class Class1
   {
       public static string someData1 = "some data 1 in Assembly1.Class1";
       public string someData2 = "some data 2 in Assembly1.Class1";

       public static string SomeMethod1()
       {
           //return Assembly2.Class2.someData1;
           return null;
       }

       public string SomeMethod2()
       {
           //Assembly2.Class2 c = new Assembly2.Class2();
           //return c.someData2;
           return null;
       }
   }
}

Pay attention to Assembly1, here is a trick. I replace "return
Assembly2.Class2.someData1;" with "return null;" in SomeMethods1() and do
similar thing in SomeMethods2().

2. Use the following command to build Assembly1 firstly:
csc .exe /t:library /out: Assembly1\bin\Debug\Assembly1.dll Assembly1\*.cs

3. Build Assembly2:
csc .exe /t:library /out: Assembly2\bin\Debug\Assembly2.dll /reference:
Assembly1\bin\Debug\Assembly1.dll Assembly2\*.cs

4. Uncomment the "return Assembly2.Class2.someData1;" and comment "return
null;" in Assembly1.Class1.SomeMethod1(), and do similar thing in
SomeMethods2(). Now, the code in Assembly1 looks like the following:

namespace Assembly1
{
   public class Class1
   {
       public static string someData1 = "some data 1 in Assembly1.Class1";
       public string someData2 = "some data 2 in Assembly1.Class1";

       public static string SomeMethod1()
       {
           return Assembly2.Class2.someData1;
           //return null;
       }

       public string SomeMethod2()
       {
           Assembly2.Class2 c = new Assembly2.Class2();
           return c.someData2;
           //return null;
       }
   }
}

5. Build Assembly1:
csc .exe /t:library /out: Assembly1\bin\Debug\Assembly1.dll /reference:
Assembly2\bin\Debug\Assembly2.dll Assembly1\*.cs

6. Build the whole app
csc /t:exe /out:App\bin\Debug\App.exe
/reference:Assembly1\bin\Debug\Assembly1.dll,Assembly2\bin\Debug\Assembly2.d
ll App\*.cs

7. Now, the two assemblies reference each other.

Regards,
Jialiang Ge (jialge@online.microsoft.com, remove 'online.')
Microsoft Online Community Support

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Pull the interface out to a second J# project. Let both original
projects reference the interface project.

Cheers,

Maxwell