Exposing C# Objects to COM
Just as an RCW proxy wraps a COM object when you access it from C#, code that accesses a C# object as a COM object must do so through a proxy as well. When your C# object is marshaled out to COM, the runtime creates a COM Callable Wrapper (CCW). The CCW follows the same lifetime rules as other COM objects, and as long as it is alive, a CCW maintains a traceable reference to the object it wraps. This keeps the object alive when the garbage collector is run.
The following example shows how you can export both a class and an interface
from C# and control the Global Unique Identifiers (GUIDs) and Dispatch IDs
(DISPIDs) assigned. After compiling IRunInfo
and
StackSnapshot
, you can
register both using RegAsm.exe.
// IRunInfo.cs // Compile with: // csc /t:library IRunInfo.cs using System; using System.Runtime.InteropServices; [GuidAttribute("aa6b10a2-dc4f-4a24-ae5e-90362c2142c1")] public interface IRunInfo { [DispId(1)] string GetRunInfo(); } // StackSnapshot.cs // compile with csc /t:library /r:IRunInfo.dll StackSnapShot.cs using System; using System.Runtime.InteropServices; using System.Diagnostics; [GuidAttribute("b72ccf55-88cc-4657-8577-72bd0ff767bc")] public class StackSnapshot : IRunInfo { public StackSnapshot() { st = new StackTrace(); } [DispId(1)] public string GetRunInfo() { return st.ToString(); } private StackTrace st; }
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