RAD Studio for Microsoft .NET - Embarcadero Technologies

1.2 Developing Applications with RAD Studio for Microsoft .NET Using COM Interop in Managed
your forms as you would with any .NET component.
The following topics are covered in this overview:
• Introduction to the terminology of COM Interop. If you are already familiar with these concepts, you can skip directly to the
section on RAD Studio IDE features and tools for COM/Interop.
• Introduction to some of the .NET Framework SDK tools for working with COM/Interop.
• Using COM Interop Assemblies in the IDE.
COM Interop Overview
Seamless interoperability is achieved through stand-in objects called Runtime Callable Wrappers (RCW). The RCW is a layer of
communication between your managed application, and the actual unmanaged COM server.
COM Interop Terminology
The .NET Framework has a rich collection of terms and three-letter acronyms. This section will help you understand the
terminology you will encounter when reading other COM Interop literature.
Metadata
In the context of .NET and COM, metadata is a term used to mean type information. In COM, type information can be stored in a
variety of ways. For instance, a C++ header file is a language-specific container for type information. A type library is also a
container for type information, but being a binary format, type libraries are language neutral. Unlike the COM development model
where type libraries are not required, language neutral metadata is mandatory for all .NET assemblies. Every assembly is
self-describing; its metadata contains complete type information, including private types and private class members.
Custom Attributes
Developers often tag program entities (such as classes and their methods) with descriptive attributes such as static, private,
protected, and public. In the .NET Framework, you can tag any entity, including classes, properties, methods, and even
assemblies themselves, with an attribute of your own design and meaning. Custom attributes are expressed in source code, and
are processed by the compiler. At the end of the build process, custom attributes are emitted into the output assembly just like all
metadata.
Reflection
A unique characteristic of the .NET Framework is that type information is not lost during the compilation process. Instead, all
metadata, including custom attributes, is emitted by the compiler into the final output assembly. Metadata is available at runtime,
through .NET Reflection services. The .NET Framework SDK provides a reflection tool called ildasm that allows the developer
to open any .NET assembly, and inspect the types declared therein. Such reflection tools often allow programmers to directly
view the IL code generated by the compiler. The RAD Studio IDE contains its own integrated reflection tool, in the form of the
meta data explorer tool that appears when you open a .NET assembly.
Global Assembly Cache
In COM, components can be deployed anywhere on the user's machine. Usually, a component's installation script records its
location in the system registry. Command-line tools such as regsvr32 and tregsvr can also add and remove COM components
from the registry. Registration of components is required in COM programming, even if the components are not intended to be
shared by multiple applications.
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