Chapter Six. An Introduction to COM Interop

No matter how good the .NET Framework is as a standalone technology, it could not possibly be successful if it did not integrate seamlessly with Microsoft's existing suite of technologies: Win32, COM/COM+/MTS, that is, the technologies formerly known as the DNA architecture. Microsoft has been touting these technologies for years and thousands of organizations and individuals have written millions of lines of code using these technologies. Few organizations have the luxury of halting functional development for six months to a year or more to completely rearchitect their applications to use .NET. Most organizations therefore will take a gradual migration approach, either integrating .NET technologies into their existing architecture, gradually replacing Win32/COM/COM+ (unmanaged) components and subsystems with software written with .NET or building an infrastructure around .NET while continuing to use unmanaged components to implement core functionality. Either of these approaches requires interoperation (Interop), which is Microsoft's word for allowing .NET (managed) applications and components to use unmanaged components and applications and unmanaged components to use managed components. Interoperation in both directions is needed to accommodate different migration strategies.