How do I pass a variables as data with gtkd signals ?

[huangyy via Digitalmars-d-learn]

I want to write a small program with gtkd. I need to use 
Signals.connectData to transfer an int type parameter to the 
callback function. I don't know how to write it. I hope someone 
can help me. It would be best if you can provide a sample code. 
Thank!