I was talking about MusicBee's side... Essentially, when there are any events for a window - mouse movement, key presses, you name it -, they are put into a queue. The program typically contains a loop that calls the Windows API to take an event from that queue and send it to the window's WindowProc. "Posting" a message to a window means that you put a user-defined event into that queue; eventually, the window's WindowProc will be called with that event, and if it knows how to process it, stuff happens... or it will just silently ignore your message.
Regarding Eclipse... maybe these help:http://emonic.sourceforge.net/html/usage.html
- Emonic is a C#/.NET 2.0 plugin for Eclipse, the link explains how it's set up.http://monodevelop.com/
- Not based on Eclipse. Mono is the opensource implementation of C#/.NET, so this should work just as well with the "real" .NET CLR.Visual Studio 2010 Express
- a free version of Visual Studio. It's a bit crippled (lacks certain refactoring features, you can't manually attach the debugger to random processes, etc.), but otherwise unlimited (no restriction on code size, all .NET features available, and no limitations on how you can license or sell your code/program).
MusicBeeInterface.cs contains all the definitions and constants used by MusicBee. (All these enums, delegates and structs are members of the MusicBeePlugin.Plugin class.)
TestCSharpDll.cs contains the rest of the class MusicBeePlugin.Plugin, notably the various well-known methods called by MusicBee to communicate with your plugin, as well as a bit of example code that illustrates how messages are sent to MusicBee and how MusicBee's notifications are handled.
Properties\AssemblyInfo.cs is auto-generated (and auto-modified) by Visual Studio and contains a bunch of attributes that define the product name, description, copyright, version etc. strings embedded into the DLL file.