autofocus in text fields

We're currently developing an application that targets both Zebra and non-Zebra devices, all with additional hardware scanners. We would like to be able to implement the EMDKManager.IMDKListener interface on a singleton service (not MainActivity class, since this class is going to be used not only by Zebra devices) but the method public void OnOpened(EMDKManager emdkManager) is never called in that service. Could you provide a little sample how this could be done?

What we do is we detect whether the application is running on Zebra device or something different and based on which device was detected, we supply a particular singleton service to dependency injection container.

The main issue we are facing is no autofocus in text fields with the scanner use. So each time we have to touch the field. We would like to use it hands free and always activate the next field after scanner input on the one before.