add Frame Handler
Registers FrameHandler which will receive preview frames from camera.
Note, that handlers can intercept frame by returning true
from FrameHandler.handleFrame. In such case no other handler will receive callbacks for current frame. Therefore, order in which handlers are added matters.
All callbacks are invoked from the worker thread, so it is safe to perform "heavy" operations.
Parameters
frame Handler
handler which will receive preview frames. Must not be null
. If it was already registered before, nothing happens.