GraphicsWindow.LastKey

Question

I created this small programm for getting keynames.

TextWindow.show()
GraphicsWindow.Show()

Start()

Sub Start
  GraphicsWindow.KeyDown = onKeyDown
endsub

Sub onKeyDown
  LK = GraphicsWindow.Lastkey
  TextWindow.Writeline(LK)
  Start()  
EndSub

 
It allways douples the resultlines in the TextWindow.

e.g.

Return 
A
A
Back
Back
Back
Back
Space
Space
Space
Space
Space
Space
Space
Space

a.s.o.

What's the reason for that curiosity?

Answer 1

Your recursively calling Start().  So while you press a key, the program continuously calls the GraphicsWindow.LastKey event and writes to the screen.  If you remove the call to Start() in the OnKeyDown subroutine, it will correct your problem.

Answer 2

RushWorks seems to have found the good solution but I'm unsure he have gived the good explaination about it.

The problem is that, when you look at compiled MSIL, GraphicsWindow.KeyDown = onKeyDown is compiled as AddHandler GraphicsWindow.KeyDown, AddressOf onKeyDown, so when you call start, you don't set the onKeyDown event, you add a new listener to this event. This explains why you go a 'Return', two 'A', four 'Back', height 'Space', ....

Maybe this behaviour should be changed because it can confuse users, but it seems to be difficult, unless we use Custom Events (in VB.NET, I don't know if there's any equivalent for C#) but then, it's unusual for 'pure' .NET developers. It's in fact the problem of the old JScript event model (adding 'onXXX' as attribute of an element). This problem was solved using an additional event system, which is not good for a simple language.

I hope I gived a good vision of the 'problem'.

---

Fremy VB & C#

Answer 3

Hi Rushworks and FremyCompany,

Thank you very much !


Horst