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Android example source code file (GestureDetector.java)

This example Android source code file (GestureDetector.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" TM.

Java - Android tags/keywords

android, content, deprecated, double_tap_timeout, gesturedetector, gesturehandler, long_press, longpress_timeout, motionevent, ondoubletaplistener, ongesturelistener, os, override, runtimeexception, show_press, unknown, velocitytracker

The GestureDetector.java Android example source code

/*
 * 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 android.content.Context;
import android.os.Build;
import android.os.Handler;
import android.os.Message;

/**
 * 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.
 * </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.
         *
         * @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);
    }

    /**
     * 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} and {@link OnDoubleTapListener} but does
     * nothing and return {@code false} for all applicable methods.
     */
    public static class SimpleOnGestureListener implements OnGestureListener, OnDoubleTapListener {
        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;
        }
    }

    // TODO: ViewConfiguration
    private int mBiggerTouchSlopSquare = 20 * 20;

    private int mTouchSlopSquare;
    private int mDoubleTapSlopSquare;
    private int mMinimumFlingVelocity;
    private int mMaximumFlingVelocity;

    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();

    // 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;
    private final OnGestureListener mListener;
    private OnDoubleTapListener mDoubleTapListener;

    private boolean mStillDown;
    private boolean mInLongPress;
    private boolean mAlwaysInTapRegion;
    private boolean mAlwaysInBiggerTapRegion;

    private MotionEvent mCurrentDownEvent;
    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 mLastMotionY;
    private float mLastMotionX;

    private boolean mIsLongpressEnabled;
    
    /**
     * True if we are at a target API level of >= Froyo or the developer can
     * explicitly set it. If true, input events with > 1 pointer will be ignored
     * so we can work side by side with multitouch gesture detectors.
     */
    private boolean mIgnoreMultitouch;

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

    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:
                dispatchLongPress();
                break;
                
            case TAP:
                // If the user's finger is still down, do not count it as a tap
                if (mDoubleTapListener != null && !mStillDown) {
                    mDoubleTapListener.onSingleTapConfirmed(mCurrentDownEvent);
                }
                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 UI thread (this is the usual situation).
     * @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.
     *
     * @throws NullPointerException if {@code listener} is null.
     */
    public GestureDetector(Context context, OnGestureListener listener) {
        this(context, listener, null);
    }

    /**
     * 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 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     
     *
     * @throws NullPointerException if {@code listener} is null.
     */
    public GestureDetector(Context context, OnGestureListener listener, Handler handler) {
        this(context, listener, handler, context != null &&
                context.getApplicationInfo().targetSdkVersion >= Build.VERSION_CODES.FROYO);
    }
    
    /**
     * 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 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
     * @param ignoreMultitouch whether events involving more than one pointer should
     * be ignored.
     *
     * @throws NullPointerException if {@code listener} is null.
     */
    public GestureDetector(Context context, OnGestureListener listener, Handler handler,
            boolean ignoreMultitouch) {
        if (handler != null) {
            mHandler = new GestureHandler(handler);
        } else {
            mHandler = new GestureHandler();
        }
        mListener = listener;
        if (listener instanceof OnDoubleTapListener) {
            setOnDoubleTapListener((OnDoubleTapListener) listener);
        }
        init(context, ignoreMultitouch);
    }

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

        // Fallback to support pre-donuts releases
        int touchSlop, doubleTapSlop;
        if (context == null) {
            //noinspection deprecation
            touchSlop = ViewConfiguration.getTouchSlop();
            doubleTapSlop = ViewConfiguration.getDoubleTapSlop();
            //noinspection deprecation
            mMinimumFlingVelocity = ViewConfiguration.getMinimumFlingVelocity();
            mMaximumFlingVelocity = ViewConfiguration.getMaximumFlingVelocity();
        } else {
            final ViewConfiguration configuration = ViewConfiguration.get(context);
            touchSlop = configuration.getScaledTouchSlop();
            doubleTapSlop = configuration.getScaledDoubleTapSlop();
            mMinimumFlingVelocity = configuration.getScaledMinimumFlingVelocity();
            mMaximumFlingVelocity = configuration.getScaledMaximumFlingVelocity();
        }
        mTouchSlopSquare = touchSlop * touchSlop;
        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;
    }

    /**
     * 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) {
        final int action = ev.getAction();
        final float y = ev.getY();
        final float x = ev.getX();

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

        boolean handled = false;

        switch (action & MotionEvent.ACTION_MASK) {
        case MotionEvent.ACTION_POINTER_DOWN:
            if (mIgnoreMultitouch) {
                // Multitouch event - abort.
                cancel();
            }
            break;

        case MotionEvent.ACTION_POINTER_UP:
            // Ending a multitouch gesture and going back to 1 finger
            if (mIgnoreMultitouch && ev.getPointerCount() == 2) {
                int index = (((action & MotionEvent.ACTION_POINTER_INDEX_MASK)
                        >> MotionEvent.ACTION_POINTER_INDEX_SHIFT) == 0) ? 1 : 0;
                mLastMotionX = ev.getX(index);
                mLastMotionY = ev.getY(index);
                mVelocityTracker.recycle();
                mVelocityTracker = VelocityTracker.obtain();
            }
            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;
                    // 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);
                }
            }

            mLastMotionX = x;
            mLastMotionY = y;
            if (mCurrentDownEvent != null) {
                mCurrentDownEvent.recycle();
            }
            mCurrentDownEvent = MotionEvent.obtain(ev);
            mAlwaysInTapRegion = true;
            mAlwaysInBiggerTapRegion = true;
            mStillDown = true;
            mInLongPress = false;
            
            if (mIsLongpressEnabled) {
                mHandler.removeMessages(LONG_PRESS);
                mHandler.sendEmptyMessageAtTime(LONG_PRESS, mCurrentDownEvent.getDownTime()
                        + TAP_TIMEOUT + LONGPRESS_TIMEOUT);
            }
            mHandler.sendEmptyMessageAtTime(SHOW_PRESS, mCurrentDownEvent.getDownTime() + TAP_TIMEOUT);
            handled |= mListener.onDown(ev);
            break;

        case MotionEvent.ACTION_MOVE:
            if (mInLongPress || (mIgnoreMultitouch && ev.getPointerCount() > 1)) {
                break;
            }
            final float scrollX = mLastMotionX - x;
            final float scrollY = mLastMotionY - y;
            if (mIsDoubleTapping) {
                // Give the move events of the double-tap
                handled |= mDoubleTapListener.onDoubleTapEvent(ev);
            } else if (mAlwaysInTapRegion) {
                final int deltaX = (int) (x - mCurrentDownEvent.getX());
                final int deltaY = (int) (y - mCurrentDownEvent.getY());
                int distance = (deltaX * deltaX) + (deltaY * deltaY);
                if (distance > mTouchSlopSquare) {
                    handled = mListener.onScroll(mCurrentDownEvent, ev, scrollX, scrollY);
                    mLastMotionX = x;
                    mLastMotionY = y;
                    mAlwaysInTapRegion = false;
                    mHandler.removeMessages(TAP);
                    mHandler.removeMessages(SHOW_PRESS);
                    mHandler.removeMessages(LONG_PRESS);
                }
                if (distance > mBiggerTouchSlopSquare) {
                    mAlwaysInBiggerTapRegion = false;
                }
            } else if ((Math.abs(scrollX) >= 1) || (Math.abs(scrollY) >= 1)) {
                handled = mListener.onScroll(mCurrentDownEvent, ev, scrollX, scrollY);
                mLastMotionX = x;
                mLastMotionY = y;
            }
            break;

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

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

                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;
            mVelocityTracker.recycle();
            mVelocityTracker = null;
            mIsDoubleTapping = false;
            mHandler.removeMessages(SHOW_PRESS);
            mHandler.removeMessages(LONG_PRESS);
            break;
        case MotionEvent.ACTION_CANCEL:
            cancel();
        }
        return handled;
    }

    private void cancel() {
        mHandler.removeMessages(SHOW_PRESS);
        mHandler.removeMessages(LONG_PRESS);
        mHandler.removeMessages(TAP);
        mVelocityTracker.recycle();
        mVelocityTracker = null;
        mIsDoubleTapping = false;
        mStillDown = false;
        if (mInLongPress) {
            mInLongPress = false;
        }
    }

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

        if (secondDown.getEventTime() - firstUp.getEventTime() > DOUBLE_TAP_TIMEOUT) {
            return false;
        }

        int deltaX = (int) firstDown.getX() - (int) secondDown.getX();
        int deltaY = (int) firstDown.getY() - (int) secondDown.getY();
        return (deltaX * deltaX + deltaY * deltaY < mDoubleTapSlopSquare);
    }

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

Other Android examples (source code examples)

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