Can you give me a hint or some sample code to turn off a layer on the current drawing?
This really needs some new methods to turn layers on and off in a simple manner. However, you have access to all the sections, tables and entities of a loaded drawing and you can modify anything directly. To turn layers on and off you can do something like this:
Yxxf D; // loaded drawing
YxxfTblLayer layer =
if (layer != null) // layer found
layer.aci = -Math.abs(layer.aci); // negative color means layer is off
Take a look at the Javadoc for Yxxf (the drawing), YxxfSecTables (the tables section) and YxxfTblLayer (the layer table) for more info and other methods that might be useful.