On StackOverflow, someone asks how to detect the GUI Window Created/Closed Event, which Unity3D does not ship an off-the-shelf solution.
Below is my solution to this problem: to use property setter to handle this. Here is the sample code:
Using Vuforia’s Unity package it is easy to develop an AR based application. The full tutorials can be found in Vuforia’s web page: Getting Started with the Unity Extension. Here is the outline: