Programming C#, Third Edition

Exporting .NET Components

You can export your .NET class for use with existing COM components, although this is an unusual requirement. The Regasm tool will register the metadata from your component in the System Registry.

Invoke Regasm with the name of the DLL, which must be installed in the GAC (see Chapter 17). For example:

Regasm myAssembly.dll

This will export your component’s metadata to the Registry. For example, you can create a new C# DLL project in which you recreate your four-function calculator, as shown in Example 22-8.

Example 22-8. The four-function calculator in a DLL

using System;
using System.Reflection;

[assembly: AssemblyKeyFile("test.key")]
namespace Programming_CSharp
{
    public class Calculator
    {
        public Calculator( )
        {
            
        }
        public Double Add (Double left, Double right)
        {
            return left + right;
        }
        public Double Subtract (Double left, Double right)
        {
            return left - right;
        }
        public Double Multiply (Double left, Double right)
        {
            return left * right;
        }
        public Double Divide (Double left, Double right)
        {
            return left / right;
        }
    }
}

Save this to a file named Calculator.cs in a project named ProgrammingCSharpDLL. Create a key, compile the program, add it to the GAC, and register it with:

sn -k test.key
csc /t:library /out:ProgrammingCSharpDLL.dll Calculator.cs
gacutil /i ProgrammingCSharpDLL.dll
Regasm ProgrammingCSharpDLL.dll

A quick check of the Registry shows that a ProgID was created for the DLL, as shown in Figure 22-17.

Figure 22-17. The Registry after registering the DLL ...