PDFNet Xamarin: How can i get position of view on PDF and re-calculate when zoom and move

[Kien Vuong]

Hi, I'm using fullversion of PDFNet. I used it for my Xamarin project. I want to add a view as overlay on top of PDF view. And when i moved or zoom that view must at the correct position.
I had googled and found some way like use onScrollChanged and onScale. But in the Tool of PdfViewCtrl i just found few listener like onMove, onUp, onScaleBegin, onLongPress and onSingleTap.
I don't know how to used another listener.
Please tell me the way or give me some example.
Thank you!