Question

Can someone explain this to me?

In Visual Studio 2010, create a VB.net Windows Forms App. Add 2 forms: Form1 and Form2. In the Form1 Load event type Form2.Close(). Now if we look in the method definition Close() is not a static (shared) method. So how is this possible to compile or to work at run time.

Furthermore, do the same thing in C# and Form2.Close(); doesn’t compile.

What’s going on? Why is this possible in VB.net and what is actually happening when that line of code is executed?

Answer 1

You’ve discovered a VB.NET-ism called "default instance".

The compiler is actually emitting this:

My.Forms.Form2.Close();

There is a nice writeup of that feature here:

The default instance is an object of that type that the VB application framework creates and manages for you.

…

If you use the default instance then you don’t need to invoke a constructor explicitly. You simply access the default instance directly via the My.Forms object