Pass message from DLL to GUI

I have created an application which consists of 3 Layers: GUI-BLL-DLL. When 开发者_如何学PythonI am loading a flat file I am doing this in the DLL but I want to show to the user the process through a progress bar in the GUI. So I want to pass the variable LineCounts from the DLL to GUI. I know that I have to use EVENTS, but how. Can someone help me to understant how to implement this event in VB.NET with code example?

Thanks in advance Elias

I suggest you look into using a BackgroundWorker. I presume you'll want to use a background thread to import the text file, and report progress intermittently: http://msdn.microsoft.com/en-us/library/system.componentmodel.backgroundworker.aspx