EventStreamTransformationpublic interface EventStreamTransformation | Interface for classes that can handle and potentially transform a stream of
motion and accessibility events. Instances implementing this interface are
ordered in a sequence to implement a transformation chain. An instance may
consume, modify, and generate events. It is responsible to deliver the
output events to the next transformation in the sequence set via
{@link #setNext(EventStreamTransformation)}.
Note that since instances implementing this interface are transformations
of the event stream, an instance should work against the event stream
potentially modified by previous ones. Hence, the order of transformations
is important.
It is a responsibility of each handler that decides to react to an event
sequence and prevent any subsequent ones from performing an action to send
the appropriate cancel event given it has delegated a part of the events
that belong to the current gesture. This will ensure that subsequent
transformations will not be left in an inconsistent state and the applications
see a consistent event stream.
For example, to cancel a {@link KeyEvent} the handler has to emit an event
with action {@link KeyEvent#ACTION_UP} with the additional flag
{@link KeyEvent#FLAG_CANCELED}. To cancel a {@link MotionEvent} the handler
has to send an event with action {@link MotionEvent#ACTION_CANCEL}.
It is a responsibility of each handler that received a cancel event to clear its
internal state and to propagate the event to the next one to enable subsequent
transformations to clear their internal state.
It is a responsibility for each transformation to start handling events only
after an event that designates the start of a well-formed event sequence.
For example, if it received a down motion event followed by a cancel motion
event, it should not handle subsequent move and up events until it gets a down. |
|
