How to set Focus to input field after user clicked in Control?

Hello ABAP gurus,

Could you please tell me a method, how ABAP can set the focus back to an input field field after the user double clicked something inside a control?

I want to loose the focus from a Tree Control and set the focus somewhere else to the let the user scan values in a standard GUI input / output field again.

This doesn't work:

CLASS lcl_event_handler IMPLEMENTATION.

...

METHOD on_item_double_click.

...

SET CURSOR FIELD gs_gui_field-matnr.

Thanks alot in advance,

Benjamin