What is the Guid attribute that appears above classes in C#?

Question

I\'ve picked up some C# code recently and one of the classes has a Guid attribute present above it. I don\'t understand what this is or what it\'s used for.

Can some

Answer 1

You might want to take a look at the ComVisibleAttribute class to learn more about the ways you can make managed classes available to unmanaged code.

The [Guid] is the exact equivalent to the .NET Type.AssemblyQualifiedName. Like

System.Object, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5561934e089

With the obvious distinction that the .NET type name is easier to read by a human. It is necessary to allow a program to discover what DLL needs to be loaded to use a type. In the .NET case, the assemblies are (usually) found by enumerating the GAC. It is file based.

COM however uses the registry. After that assembly whose source code you looked at gets built and registered then you can find back the [Guid] in the registry. Fire up regedit.exe and navigate to HKLM\Software\Classes\CLSID\{guid}. You'll see the registration key values that the runtime uses to load the CLR and the assembly.