core/java/android/view/GestureDetector.java

/*
 * Copyright (C) 2008 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 android.view;

import static android.util.StatsLog.TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__DEEP_PRESS;
import static android.util.StatsLog.TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__DOUBLE_TAP;
import static android.util.StatsLog.TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__LONG_PRESS;
import static android.util.StatsLog.TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__SCROLL;
import static android.util.StatsLog.TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__SINGLE_TAP;
import static android.util.StatsLog.TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__UNKNOWN_CLASSIFICATION;

import android.annotation.UnsupportedAppUsage;
import android.content.Context;
import android.os.Build;
import android.os.Handler;
import android.os.Message;
import android.os.SystemClock;
import android.util.StatsLog;

/**
 * Detects various gestures and events using the supplied {@link MotionEvent}s.
 * The {@link OnGestureListener} callback will notify users when a particular
 * motion event has occurred. This class should only be used with {@link MotionEvent}s
 * reported via touch (don't use for trackball events).
 *
 * To use this class:
 * <ul>
 *  <li>Create an instance of the {@code GestureDetector} for your {@link View}
 *  <li>In the {@link View#onTouchEvent(MotionEvent)} method ensure you call
 *          {@link #onTouchEvent(MotionEvent)}. The methods defined in your callback
 *          will be executed when the events occur.
 *  <li>If listening for {@link OnContextClickListener#onContextClick(MotionEvent)}
 *          you must call {@link #onGenericMotionEvent(MotionEvent)}
 *          in {@link View#onGenericMotionEvent(MotionEvent)}.
 * </ul>
 */
public class GestureDetector {
    /**
     * The listener that is used to notify when gestures occur.
     * If you want to listen for all the different gestures then implement
     * this interface. If you only want to listen for a subset it might
     * be easier to extend {@link SimpleOnGestureListener}.
     */
    public interface OnGestureListener {

        /**
         * Notified when a tap occurs with the down {@link MotionEvent}
         * that triggered it. This will be triggered immediately for
         * every down event. All other events should be preceded by this.
         *
         * @param e The down motion event.
         */
        boolean onDown(MotionEvent e);

        /**
         * The user has performed a down {@link MotionEvent} and not performed
         * a move or up yet. This event is commonly used to provide visual
         * feedback to the user to let them know that their action has been
         * recognized i.e. highlight an element.
         *
         * @param e The down motion event
         */
        void onShowPress(MotionEvent e);

        /**
         * Notified when a tap occurs with the up {@link MotionEvent}
         * that triggered it.
         *
         * @param e The up motion event that completed the first tap
         * @return true if the event is consumed, else false
         */
        boolean onSingleTapUp(MotionEvent e);

        /**
         * Notified when a scroll occurs with the initial on down {@link MotionEvent} and the
         * current move {@link MotionEvent}. The distance in x and y is also supplied for
         * convenience.
         *
         * @param e1 The first down motion event that started the scrolling.
         * @param e2 The move motion event that triggered the current onScroll.
         * @param distanceX The distance along the X axis that has been scrolled since the last
         *              call to onScroll. This is NOT the distance between {@code e1}
         *              and {@code e2}.
         * @param distanceY The distance along the Y axis that has been scrolled since the last
         *              call to onScroll. This is NOT the distance between {@code e1}
         *              and {@code e2}.
         * @return true if the event is consumed, else false
         */
        boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY);

        /**
         * Notified when a long press occurs with the initial on down {@link MotionEvent}
         * that trigged it.
         *
         * @param e The initial on down motion event that started the longpress.
         */
        void onLongPress(MotionEvent e);

        /**
         * Notified of a fling event when it occurs with the initial on down {@link MotionEvent}
         * and the matching up {@link MotionEvent}. The calculated velocity is supplied along
         * the x and y axis in pixels per second.
         *
         * @param e1 The first down motion event that started the fling.
         * @param e2 The move motion event that triggered the current onFling.
         * @param velocityX The velocity of this fling measured in pixels per second
         *              along the x axis.
         * @param velocityY The velocity of this fling measured in pixels per second
         *              along the y axis.
         * @return true if the event is consumed, else false
         */
        boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY);
    }

    /**
     * The listener that is used to notify when a double-tap or a confirmed
     * single-tap occur.
     */
    public interface OnDoubleTapListener {
        /**
         * Notified when a single-tap occurs.
         * <p>
         * Unlike {@link OnGestureListener#onSingleTapUp(MotionEvent)}, this
         * will only be called after the detector is confident that the user's
         * first tap is not followed by a second tap leading to a double-tap
         * gesture.
         *
         * @param e The down motion event of the single-tap.
         * @return true if the event is consumed, else false
         */
        boolean onSingleTapConfirmed(MotionEvent e);
 
        /**
         * Notified when a double-tap occurs. Triggered on the down event of second tap.
         *
         * @param e The down motion event of the first tap of the double-tap.
         * @return true if the event is consumed, else false
         */
        boolean onDoubleTap(MotionEvent e);

        /**
         * Notified when an event within a double-tap gesture occurs, including
         * the down, move, and up events.
         *
         * @param e The motion event that occurred during the double-tap gesture.
         * @return true if the event is consumed, else false
         */
        boolean onDoubleTapEvent(MotionEvent e);
    }

    /**
     * The listener that is used to notify when a context click occurs. When listening for a
     * context click ensure that you call {@link #onGenericMotionEvent(MotionEvent)} in
     * {@link View#onGenericMotionEvent(MotionEvent)}.
     */
    public interface OnContextClickListener {
        /**
         * Notified when a context click occurs.
         *
         * @param e The motion event that occurred during the context click.
         * @return true if the event is consumed, else false
         */
        boolean onContextClick(MotionEvent e);
    }

    /**
     * A convenience class to extend when you only want to listen for a subset
     * of all the gestures. This implements all methods in the
     * {@link OnGestureListener}, {@link OnDoubleTapListener}, and {@link OnContextClickListener}
     * but does nothing and return {@code false} for all applicable methods.
     */
    public static class SimpleOnGestureListener implements OnGestureListener, OnDoubleTapListener,
            OnContextClickListener {

        public boolean onSingleTapUp(MotionEvent e) {
            return false;
        }

        public void onLongPress(MotionEvent e) {
        }

        public boolean onScroll(MotionEvent e1, MotionEvent e2,
                float distanceX, float distanceY) {
            return false;
        }

        public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,
                float velocityY) {
            return false;
        }

        public void onShowPress(MotionEvent e) {
        }

        public boolean onDown(MotionEvent e) {
            return false;
        }

        public boolean onDoubleTap(MotionEvent e) {
            return false;
        }

        public boolean onDoubleTapEvent(MotionEvent e) {
            return false;
        }

        public boolean onSingleTapConfirmed(MotionEvent e) {
            return false;
        }

        public boolean onContextClick(MotionEvent e) {
            return false;
        }
    }

    @UnsupportedAppUsage
    private int mTouchSlopSquare;
    private int mDoubleTapTouchSlopSquare;
    private int mDoubleTapSlopSquare;
    @UnsupportedAppUsage
    private int mMinimumFlingVelocity;
    private int mMaximumFlingVelocity;

    @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P)
    private static final int LONGPRESS_TIMEOUT = ViewConfiguration.getLongPressTimeout();
    private static final int TAP_TIMEOUT = ViewConfiguration.getTapTimeout();
    private static final int DOUBLE_TAP_TIMEOUT = ViewConfiguration.getDoubleTapTimeout();
    private static final int DOUBLE_TAP_MIN_TIME = ViewConfiguration.getDoubleTapMinTime();

    // constants for Message.what used by GestureHandler below
    private static final int SHOW_PRESS = 1;
    private static final int LONG_PRESS = 2;
    private static final int TAP = 3;

    private final Handler mHandler;
    @UnsupportedAppUsage
    private final OnGestureListener mListener;
    private OnDoubleTapListener mDoubleTapListener;
    private OnContextClickListener mContextClickListener;

    private boolean mStillDown;
    private boolean mDeferConfirmSingleTap;
    private boolean mInLongPress;
    private boolean mInContextClick;
    @UnsupportedAppUsage
    private boolean mAlwaysInTapRegion;
    private boolean mAlwaysInBiggerTapRegion;
    private boolean mIgnoreNextUpEvent;
    // Whether a classification has been recorded by statsd for the current event stream. Reset on
    // ACTION_DOWN.
    private boolean mHasRecordedClassification;

    private MotionEvent mCurrentDownEvent;
    private MotionEvent mCurrentMotionEvent;
    private MotionEvent mPreviousUpEvent;

    /**
     * True when the user is still touching for the second tap (down, move, and
     * up events). Can only be true if there is a double tap listener attached.
     */
    private boolean mIsDoubleTapping;

    private float mLastFocusX;
    private float mLastFocusY;
    private float mDownFocusX;
    private float mDownFocusY;

    private boolean mIsLongpressEnabled;

    /**
     * Determines speed during touch scrolling
     */
    private VelocityTracker mVelocityTracker;

    /**
     * Consistency verifier for debugging purposes.
     */
    private final InputEventConsistencyVerifier mInputEventConsistencyVerifier =
            InputEventConsistencyVerifier.isInstrumentationEnabled() ?
                    new InputEventConsistencyVerifier(this, 0) : null;

    private class GestureHandler extends Handler {
        GestureHandler() {
            super();
        }

        GestureHandler(Handler handler) {
            super(handler.getLooper());
        }

        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case SHOW_PRESS:
                    mListener.onShowPress(mCurrentDownEvent);
                    break;

                case LONG_PRESS:
                    recordGestureClassification(msg.arg1);
                    dispatchLongPress();
                    break;

                case TAP:
                    // If the user's finger is still down, do not count it as a tap
                    if (mDoubleTapListener != null) {
                        if (!mStillDown) {
                            recordGestureClassification(
                                    TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__SINGLE_TAP);
                            mDoubleTapListener.onSingleTapConfirmed(mCurrentDownEvent);
                        } else {
                            mDeferConfirmSingleTap = true;
                        }
                    }
                    break;

                default:
                    throw new RuntimeException("Unknown message " + msg); //never
            }
        }
    }

    /**
     * Creates a GestureDetector with the supplied listener.
     * This variant of the constructor should be used from a non-UI thread 
     * (as it allows specifying the Handler).
     * 
     * @param listener the listener invoked for all the callbacks, this must
     * not be null.
     * @param handler the handler to use
     *
     * @throws NullPointerException if either {@code listener} or
     * {@code handler} is null.
     *
     * @deprecated Use {@link #GestureDetector(android.content.Context,
     *      android.view.GestureDetector.OnGestureListener, android.os.Handler)} instead.
     */
    @Deprecated
    public GestureDetector(OnGestureListener listener, Handler handler) {
        this(null, listener, handler);
    }

    /**
     * Creates a GestureDetector with the supplied listener.
     * You may only use this constructor from a UI thread (this is the usual situation).
     * @see android.os.Handler#Handler()
     * 
     * @param listener the listener invoked for all the callbacks, this must
     * not be null.
     * 
     * @throws NullPointerException if {@code listener} is null.
     *
     * @deprecated Use {@link #GestureDetector(android.content.Context,
     *      android.view.GestureDetector.OnGestureListener)} instead.
     */
    @Deprecated
    public GestureDetector(OnGestureListener listener) {
        this(null, listener, null);
    }

    /**
     * Creates a GestureDetector with the supplied listener.
     * You may only use this constructor from a {@link android.os.Looper} thread.
     * @see android.os.Handler#Handler()
     *
     * @param context the application's context
     * @param listener the listener invoked for all the callbacks, this must
     * not be null. If the listener implements the {@link OnDoubleTapListener} or
     * {@link OnContextClickListener} then it will also be set as the listener for
     * these callbacks (for example when using the {@link SimpleOnGestureListener}).
     *
     * @throws NullPointerException if {@code listener} is null.
     */
    public GestureDetector(Context context, OnGestureListener listener) {
        this(context, listener, null);
    }

    /**
     * Creates a GestureDetector with the supplied listener that runs deferred events on the
     * thread associated with the supplied {@link android.os.Handler}.
     * @see android.os.Handler#Handler()
     *
     * @param context the application's context
     * @param listener the listener invoked for all the callbacks, this must
     * not be null. If the listener implements the {@link OnDoubleTapListener} or
     * {@link OnContextClickListener} then it will also be set as the listener for
     * these callbacks (for example when using the {@link SimpleOnGestureListener}).
     * @param handler the handler to use for running deferred listener events.
     *
     * @throws NullPointerException if {@code listener} is null.
     */
    public GestureDetector(Context context, OnGestureListener listener, Handler handler) {
        if (handler != null) {
            mHandler = new GestureHandler(handler);
        } else {
            mHandler = new GestureHandler();
        }
        mListener = listener;
        if (listener instanceof OnDoubleTapListener) {
            setOnDoubleTapListener((OnDoubleTapListener) listener);
        }
        if (listener instanceof OnContextClickListener) {
            setContextClickListener((OnContextClickListener) listener);
        }
        init(context);
    }
    
    /**
     * Creates a GestureDetector with the supplied listener that runs deferred events on the
     * thread associated with the supplied {@link android.os.Handler}.
     * @see android.os.Handler#Handler()
     *
     * @param context the application's context
     * @param listener the listener invoked for all the callbacks, this must
     * not be null.
     * @param handler the handler to use for running deferred listener events.
     * @param unused currently not used.
     *
     * @throws NullPointerException if {@code listener} is null.
     */
    public GestureDetector(Context context, OnGestureListener listener, Handler handler,
            boolean unused) {
        this(context, listener, handler);
    }

    private void init(Context context) {
        if (mListener == null) {
            throw new NullPointerException("OnGestureListener must not be null");
        }
        mIsLongpressEnabled = true;

        // Fallback to support pre-donuts releases
        int touchSlop, doubleTapSlop, doubleTapTouchSlop;
        if (context == null) {
            //noinspection deprecation
            touchSlop = ViewConfiguration.getTouchSlop();
            doubleTapTouchSlop = touchSlop; // Hack rather than adding a hidden method for this
            doubleTapSlop = ViewConfiguration.getDoubleTapSlop();
            //noinspection deprecation
            mMinimumFlingVelocity = ViewConfiguration.getMinimumFlingVelocity();
            mMaximumFlingVelocity = ViewConfiguration.getMaximumFlingVelocity();
        } else {
            final ViewConfiguration configuration = ViewConfiguration.get(context);
            touchSlop = configuration.getScaledTouchSlop();
            doubleTapTouchSlop = configuration.getScaledDoubleTapTouchSlop();
            doubleTapSlop = configuration.getScaledDoubleTapSlop();
            mMinimumFlingVelocity = configuration.getScaledMinimumFlingVelocity();
            mMaximumFlingVelocity = configuration.getScaledMaximumFlingVelocity();
        }
        mTouchSlopSquare = touchSlop * touchSlop;
        mDoubleTapTouchSlopSquare = doubleTapTouchSlop * doubleTapTouchSlop;
        mDoubleTapSlopSquare = doubleTapSlop * doubleTapSlop;
    }

    /**
     * Sets the listener which will be called for double-tap and related
     * gestures.
     * 
     * @param onDoubleTapListener the listener invoked for all the callbacks, or
     *        null to stop listening for double-tap gestures.
     */
    public void setOnDoubleTapListener(OnDoubleTapListener onDoubleTapListener) {
        mDoubleTapListener = onDoubleTapListener;
    }

    /**
     * Sets the listener which will be called for context clicks.
     *
     * @param onContextClickListener the listener invoked for all the callbacks, or null to stop
     *            listening for context clicks.
     */
    public void setContextClickListener(OnContextClickListener onContextClickListener) {
        mContextClickListener = onContextClickListener;
    }

    /**
     * Set whether longpress is enabled, if this is enabled when a user
     * presses and holds down you get a longpress event and nothing further.
     * If it's disabled the user can press and hold down and then later
     * moved their finger and you will get scroll events. By default
     * longpress is enabled.
     *
     * @param isLongpressEnabled whether longpress should be enabled.
     */
    public void setIsLongpressEnabled(boolean isLongpressEnabled) {
        mIsLongpressEnabled = isLongpressEnabled;
    }

    /**
     * @return true if longpress is enabled, else false.
     */
    public boolean isLongpressEnabled() {
        return mIsLongpressEnabled;
    }

    /**
     * Analyzes the given motion event and if applicable triggers the
     * appropriate callbacks on the {@link OnGestureListener} supplied.
     *
     * @param ev The current motion event.
     * @return true if the {@link OnGestureListener} consumed the event,
     *              else false.
     */
    public boolean onTouchEvent(MotionEvent ev) {
        if (mInputEventConsistencyVerifier != null) {
            mInputEventConsistencyVerifier.onTouchEvent(ev, 0);
        }

        final int action = ev.getAction();

        if (mCurrentMotionEvent != null) {
            mCurrentMotionEvent.recycle();
        }
        mCurrentMotionEvent = MotionEvent.obtain(ev);

        if (mVelocityTracker == null) {
            mVelocityTracker = VelocityTracker.obtain();
        }
        mVelocityTracker.addMovement(ev);

        final boolean pointerUp =
                (action & MotionEvent.ACTION_MASK) == MotionEvent.ACTION_POINTER_UP;
        final int skipIndex = pointerUp ? ev.getActionIndex() : -1;
        final boolean isGeneratedGesture =
                (ev.getFlags() & MotionEvent.FLAG_IS_GENERATED_GESTURE) != 0;

        // Determine focal point
        float sumX = 0, sumY = 0;
        final int count = ev.getPointerCount();
        for (int i = 0; i < count; i++) {
            if (skipIndex == i) continue;
            sumX += ev.getX(i);
            sumY += ev.getY(i);
        }
        final int div = pointerUp ? count - 1 : count;
        final float focusX = sumX / div;
        final float focusY = sumY / div;

        boolean handled = false;

        switch (action & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_POINTER_DOWN:
                mDownFocusX = mLastFocusX = focusX;
                mDownFocusY = mLastFocusY = focusY;
                // Cancel long press and taps
                cancelTaps();
                break;

            case MotionEvent.ACTION_POINTER_UP:
                mDownFocusX = mLastFocusX = focusX;
                mDownFocusY = mLastFocusY = focusY;

                // Check the dot product of current velocities.
                // If the pointer that left was opposing another velocity vector, clear.
                mVelocityTracker.computeCurrentVelocity(1000, mMaximumFlingVelocity);
                final int upIndex = ev.getActionIndex();
                final int id1 = ev.getPointerId(upIndex);
                final float x1 = mVelocityTracker.getXVelocity(id1);
                final float y1 = mVelocityTracker.getYVelocity(id1);
                for (int i = 0; i < count; i++) {
                    if (i == upIndex) continue;

                    final int id2 = ev.getPointerId(i);
                    final float x = x1 * mVelocityTracker.getXVelocity(id2);
                    final float y = y1 * mVelocityTracker.getYVelocity(id2);

                    final float dot = x + y;
                    if (dot < 0) {
                        mVelocityTracker.clear();
                        break;
                    }
                }
                break;

            case MotionEvent.ACTION_DOWN:
                if (mDoubleTapListener != null) {
                    boolean hadTapMessage = mHandler.hasMessages(TAP);
                    if (hadTapMessage) mHandler.removeMessages(TAP);
                    if ((mCurrentDownEvent != null) && (mPreviousUpEvent != null)
                            && hadTapMessage
                            && isConsideredDoubleTap(mCurrentDownEvent, mPreviousUpEvent, ev)) {
                        // This is a second tap
                        mIsDoubleTapping = true;
                        recordGestureClassification(
                                TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__DOUBLE_TAP);
                        // Give a callback with the first tap of the double-tap
                        handled |= mDoubleTapListener.onDoubleTap(mCurrentDownEvent);
                        // Give a callback with down event of the double-tap
                        handled |= mDoubleTapListener.onDoubleTapEvent(ev);
                    } else {
                        // This is a first tap
                        mHandler.sendEmptyMessageDelayed(TAP, DOUBLE_TAP_TIMEOUT);
                    }
                }

                mDownFocusX = mLastFocusX = focusX;
                mDownFocusY = mLastFocusY = focusY;
                if (mCurrentDownEvent != null) {
                    mCurrentDownEvent.recycle();
                }
                mCurrentDownEvent = MotionEvent.obtain(ev);
                mAlwaysInTapRegion = true;
                mAlwaysInBiggerTapRegion = true;
                mStillDown = true;
                mInLongPress = false;
                mDeferConfirmSingleTap = false;
                mHasRecordedClassification = false;

                if (mIsLongpressEnabled) {
                    mHandler.removeMessages(LONG_PRESS);
                    mHandler.sendMessageAtTime(
                            mHandler.obtainMessage(
                                    LONG_PRESS,
                                    TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__LONG_PRESS,
                                    0 /* arg2 */),
                            mCurrentDownEvent.getDownTime()
                                    + ViewConfiguration.getLongPressTimeout());
                }
                mHandler.sendEmptyMessageAtTime(SHOW_PRESS,
                        mCurrentDownEvent.getDownTime() + TAP_TIMEOUT);
                handled |= mListener.onDown(ev);
                break;

            case MotionEvent.ACTION_MOVE:
                if (mInLongPress || mInContextClick) {
                    break;
                }

                final int motionClassification = ev.getClassification();
                final boolean hasPendingLongPress = mHandler.hasMessages(LONG_PRESS);

                final float scrollX = mLastFocusX - focusX;
                final float scrollY = mLastFocusY - focusY;
                if (mIsDoubleTapping) {
                    // Give the move events of the double-tap
                    recordGestureClassification(
                            TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__DOUBLE_TAP);
                    handled |= mDoubleTapListener.onDoubleTapEvent(ev);
                } else if (mAlwaysInTapRegion) {
                    final int deltaX = (int) (focusX - mDownFocusX);
                    final int deltaY = (int) (focusY - mDownFocusY);
                    int distance = (deltaX * deltaX) + (deltaY * deltaY);
                    int slopSquare = isGeneratedGesture ? 0 : mTouchSlopSquare;

                    final boolean ambiguousGesture =
                            motionClassification == MotionEvent.CLASSIFICATION_AMBIGUOUS_GESTURE;
                    final boolean shouldInhibitDefaultAction =
                            hasPendingLongPress && ambiguousGesture;
                    if (shouldInhibitDefaultAction) {
                        // Inhibit default long press
                        final float multiplier = ViewConfiguration.getAmbiguousGestureMultiplier();
                        if (distance > slopSquare) {
                            // The default action here is to remove long press. But if the touch
                            // slop below gets increased, and we never exceed the modified touch
                            // slop while still receiving AMBIGUOUS_GESTURE, we risk that *nothing*
                            // will happen in response to user input. To prevent this,
                            // reschedule long press with a modified timeout.
                            mHandler.removeMessages(LONG_PRESS);
                            final long longPressTimeout = ViewConfiguration.getLongPressTimeout();
                            mHandler.sendMessageAtTime(
                                    mHandler.obtainMessage(
                                            LONG_PRESS,
                                            TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__LONG_PRESS,
                                            0 /* arg2 */),
                                    ev.getDownTime() + (long) (longPressTimeout * multiplier));
                        }
                        // Inhibit default scroll. If a gesture is ambiguous, we prevent scroll
                        // until the gesture is resolved.
                        // However, for safety, simply increase the touch slop in case the
                        // classification is erroneous. Since the value is squared, multiply twice.
                        slopSquare *= multiplier * multiplier;
                    }

                    if (distance > slopSquare) {
                        recordGestureClassification(
                                TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__SCROLL);
                        handled = mListener.onScroll(mCurrentDownEvent, ev, scrollX, scrollY);
                        mLastFocusX = focusX;
                        mLastFocusY = focusY;
                        mAlwaysInTapRegion = false;
                        mHandler.removeMessages(TAP);
                        mHandler.removeMessages(SHOW_PRESS);
                        mHandler.removeMessages(LONG_PRESS);
                    }
                    int doubleTapSlopSquare = isGeneratedGesture ? 0 : mDoubleTapTouchSlopSquare;
                    if (distance > doubleTapSlopSquare) {
                        mAlwaysInBiggerTapRegion = false;
                    }
                } else if ((Math.abs(scrollX) >= 1) || (Math.abs(scrollY) >= 1)) {
                    recordGestureClassification(TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__SCROLL);
                    handled = mListener.onScroll(mCurrentDownEvent, ev, scrollX, scrollY);
                    mLastFocusX = focusX;
                    mLastFocusY = focusY;
                }
                final boolean deepPress =
                        motionClassification == MotionEvent.CLASSIFICATION_DEEP_PRESS;
                if (deepPress && hasPendingLongPress) {
                    mHandler.removeMessages(LONG_PRESS);
                    mHandler.sendMessage(
                            mHandler.obtainMessage(
                                  LONG_PRESS,
                                  TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__DEEP_PRESS,
                                  0 /* arg2 */));
                }
                break;

            case MotionEvent.ACTION_UP:
                mStillDown = false;
                MotionEvent currentUpEvent = MotionEvent.obtain(ev);
                if (mIsDoubleTapping) {
                    // Finally, give the up event of the double-tap
                    recordGestureClassification(
                            TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__DOUBLE_TAP);
                    handled |= mDoubleTapListener.onDoubleTapEvent(ev);
                } else if (mInLongPress) {
                    mHandler.removeMessages(TAP);
                    mInLongPress = false;
                } else if (mAlwaysInTapRegion && !mIgnoreNextUpEvent) {
                    recordGestureClassification(
                            TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__SINGLE_TAP);
                    handled = mListener.onSingleTapUp(ev);
                    if (mDeferConfirmSingleTap && mDoubleTapListener != null) {
                        mDoubleTapListener.onSingleTapConfirmed(ev);
                    }
                } else if (!mIgnoreNextUpEvent) {

                    // A fling must travel the minimum tap distance
                    final VelocityTracker velocityTracker = mVelocityTracker;
                    final int pointerId = ev.getPointerId(0);
                    velocityTracker.computeCurrentVelocity(1000, mMaximumFlingVelocity);
                    final float velocityY = velocityTracker.getYVelocity(pointerId);
                    final float velocityX = velocityTracker.getXVelocity(pointerId);

                    if ((Math.abs(velocityY) > mMinimumFlingVelocity)
                            || (Math.abs(velocityX) > mMinimumFlingVelocity)) {
                        handled = mListener.onFling(mCurrentDownEvent, ev, velocityX, velocityY);
                    }
                }
                if (mPreviousUpEvent != null) {
                    mPreviousUpEvent.recycle();
                }
                // Hold the event we obtained above - listeners may have changed the original.
                mPreviousUpEvent = currentUpEvent;
                if (mVelocityTracker != null) {
                    // This may have been cleared when we called out to the
                    // application above.
                    mVelocityTracker.recycle();
                    mVelocityTracker = null;
                }
                mIsDoubleTapping = false;
                mDeferConfirmSingleTap = false;
                mIgnoreNextUpEvent = false;
                mHandler.removeMessages(SHOW_PRESS);
                mHandler.removeMessages(LONG_PRESS);
                break;

            case MotionEvent.ACTION_CANCEL:
                cancel();
                break;
        }

        if (!handled && mInputEventConsistencyVerifier != null) {
            mInputEventConsistencyVerifier.onUnhandledEvent(ev, 0);
        }
        return handled;
    }

    /**
     * Analyzes the given generic motion event and if applicable triggers the
     * appropriate callbacks on the {@link OnGestureListener} supplied.
     *
     * @param ev The current motion event.
     * @return true if the {@link OnGestureListener} consumed the event,
     *              else false.
     */
    public boolean onGenericMotionEvent(MotionEvent ev) {
        if (mInputEventConsistencyVerifier != null) {
            mInputEventConsistencyVerifier.onGenericMotionEvent(ev, 0);
        }

        final int actionButton = ev.getActionButton();
        switch (ev.getActionMasked()) {
            case MotionEvent.ACTION_BUTTON_PRESS:
                if (mContextClickListener != null && !mInContextClick && !mInLongPress
                        && (actionButton == MotionEvent.BUTTON_STYLUS_PRIMARY
                        || actionButton == MotionEvent.BUTTON_SECONDARY)) {
                    if (mContextClickListener.onContextClick(ev)) {
                        mInContextClick = true;
                        mHandler.removeMessages(LONG_PRESS);
                        mHandler.removeMessages(TAP);
                        return true;
                    }
                }
                break;

            case MotionEvent.ACTION_BUTTON_RELEASE:
                if (mInContextClick && (actionButton == MotionEvent.BUTTON_STYLUS_PRIMARY
                        || actionButton == MotionEvent.BUTTON_SECONDARY)) {
                    mInContextClick = false;
                    mIgnoreNextUpEvent = true;
                }
                break;
        }
        return false;
    }

    private void cancel() {
        mHandler.removeMessages(SHOW_PRESS);
        mHandler.removeMessages(LONG_PRESS);
        mHandler.removeMessages(TAP);
        mVelocityTracker.recycle();
        mVelocityTracker = null;
        mIsDoubleTapping = false;
        mStillDown = false;
        mAlwaysInTapRegion = false;
        mAlwaysInBiggerTapRegion = false;
        mDeferConfirmSingleTap = false;
        mInLongPress = false;
        mInContextClick = false;
        mIgnoreNextUpEvent = false;
    }

    private void cancelTaps() {
        mHandler.removeMessages(SHOW_PRESS);
        mHandler.removeMessages(LONG_PRESS);
        mHandler.removeMessages(TAP);
        mIsDoubleTapping = false;
        mAlwaysInTapRegion = false;
        mAlwaysInBiggerTapRegion = false;
        mDeferConfirmSingleTap = false;
        mInLongPress = false;
        mInContextClick = false;
        mIgnoreNextUpEvent = false;
    }

    private boolean isConsideredDoubleTap(MotionEvent firstDown, MotionEvent firstUp,
            MotionEvent secondDown) {
        if (!mAlwaysInBiggerTapRegion) {
            return false;
        }

        final long deltaTime = secondDown.getEventTime() - firstUp.getEventTime();
        if (deltaTime > DOUBLE_TAP_TIMEOUT || deltaTime < DOUBLE_TAP_MIN_TIME) {
            return false;
        }

        int deltaX = (int) firstDown.getX() - (int) secondDown.getX();
        int deltaY = (int) firstDown.getY() - (int) secondDown.getY();
        final boolean isGeneratedGesture =
                (firstDown.getFlags() & MotionEvent.FLAG_IS_GENERATED_GESTURE) != 0;
        int slopSquare = isGeneratedGesture ? 0 : mDoubleTapSlopSquare;
        return (deltaX * deltaX + deltaY * deltaY < slopSquare);
    }

    private void dispatchLongPress() {
        mHandler.removeMessages(TAP);
        mDeferConfirmSingleTap = false;
        mInLongPress = true;
        mListener.onLongPress(mCurrentDownEvent);
    }

    private void recordGestureClassification(int classification) {
        if (mHasRecordedClassification
                || classification
                    == TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__UNKNOWN_CLASSIFICATION) {
            // Only record the first classification for an event stream.
            return;
        }
        if (mCurrentDownEvent == null || mCurrentMotionEvent == null) {
            // If the complete event stream wasn't seen, don't record anything.
            mHasRecordedClassification = true;
            return;
        }
        StatsLog.write(
                StatsLog.TOUCH_GESTURE_CLASSIFIED,
                getClass().getName(),
                classification,
                (int) (SystemClock.uptimeMillis() - mCurrentMotionEvent.getDownTime()),
                (float) Math.hypot(mCurrentMotionEvent.getRawX() - mCurrentDownEvent.getRawX(),
                                   mCurrentMotionEvent.getRawY() - mCurrentDownEvent.getRawY()));
        mHasRecordedClassification = true;
    }
}