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/*
** Copyright 2012, The Android Open Source Project
**
** Licensed under the Apache License, Version 2.0 (the "License");
** you may not use this file except in compliance with the License.
** You may obtain a copy of the License at
**
** http://www.apache.org/licenses/LICENSE-2.0
**
** Unless required by applicable law or agreed to in writing, software
** distributed under the License is distributed on an "AS IS" BASIS,
** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
** See the License for the specific language governing permissions and
** limitations under the License.
*/
package com.android.server.accessibility;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.accessibility.AccessibilityEvent;
/**
* 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.
*/
interface EventStreamTransformation {
/**
* Receives a motion event. Passed are the event transformed by previous
* transformations and the raw event to which no transformations have
* been applied.
*
* @param event The transformed motion event.
* @param rawEvent The raw motion event.
* @param policyFlags Policy flags for the event.
*/
public void onMotionEvent(MotionEvent event, MotionEvent rawEvent, int policyFlags);
/**
* Receives an accessibility event.
*
* @param event The accessibility event.
*/
public void onAccessibilityEvent(AccessibilityEvent event);
/**
* Sets the next transformation.
*
* @param next The next transformation.
*/
public void setNext(EventStreamTransformation next);
/**
* Clears the internal state of this transformation.
*/
public void clear();
/**
* Destroys this transformation.
*/
public void onDestroy();
}
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