Android開發之手勢識別

在播放器中，涉及到手勢識別。所以，今天我們來說一下Android的手勢識別。

我們首先需要站在巨人的肩膀上。引用一些別人的案例和說明。

第一篇：

/kf/201110/109480.html

對於觸摸屏，其原生的消息無非按下、抬起、移動這幾種，我們只需要簡單重載onTouch或者設置觸摸偵聽器setOnTouchListener即可進行處理。不過，為了提高我們的APP的用戶體驗，有時候我們需要識別用戶的手勢，Android給我們提供的手勢識別工具GestureDetector就可以幫上大忙了。

基礎

GestureDetector的工作原理是，當我們接收到用戶觸摸消息時，將這個消息交給GestureDetector去加工，我們通過設置偵聽器獲得GestureDetector處理後的手勢。


GestureDetector提供了兩個偵聽器接口，OnGestureListener處理單擊類消息，OnDoubleTapListener處理雙擊類消息。


OnGestureListener的接口有這幾個：


// 單擊，觸摸屏按下時立刻觸發


abstract boolean onDown(MotionEvent e);


// 抬起，手指離開觸摸屏時觸發(長按、滾動、滑動時，不會觸發這個手勢)


abstract boolean onSingleTapUp(MotionEvent e);


// 短按，觸摸屏按下後片刻後抬起，會觸發這個手勢，如果迅速抬起則不會


abstract void onShowPress(MotionEvent e);


// 長按，觸摸屏按下後既不抬起也不移動，過一段時間後觸發


abstract void onLongPress(MotionEvent e);


// 滾動，觸摸屏按下後移動


abstract boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY);


// 滑動，觸摸屏按下後快速移動並抬起，會先觸發滾動手勢，跟著觸發一個滑動手勢


abstract boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY);


OnDoubleTapListener的接口有這幾個：


// 雙擊，手指在觸摸屏上迅速點擊第二下時觸發


abstract boolean onDoubleTap(MotionEvent e);


// 雙擊的按下跟抬起各觸發一次


abstract boolean onDoubleTapEvent(MotionEvent e);


// 單擊確認，即很快的按下並抬起，但並不連續點擊第二下


abstract boolean onSingleTapConfirmed(MotionEvent e);


有時候我們並不需要處理上面所有手勢，方便起見，Android提供了另外一個類SimpleOnGestureListener實現了如上接口，我們只需要繼承SimpleOnGestureListener然後重載感興趣的手勢即可。

簡單應用

import android.content.Context; 

import android.view.MotionEvent; 

import android.view.GestureDetector.SimpleOnGestureListener; 

import android.widget.Toast; 

 

public class MyGestureListener extends SimpleOnGestureListener { 

 

    private Context mContext; 

     

    MyGestureListener(Context context) { 

        mContext = context; 

    } 

     

    @Override 

    public boolean onDown(MotionEvent e) { 

        Toast.makeText(mContext, "DOWN " + e.getAction(), Toast.LENGTH_SHORT).show(); 

        return false; 

    } 

 

    @Override 

    public void onShowPress(MotionEvent e) { 

        Toast.makeText(mContext, "SHOW " + e.getAction(), Toast.LENGTH_SHORT).show();            

    } 

 

    @Override 

    public boolean onSingleTapUp(MotionEvent e) { 

        Toast.makeText(mContext, "SINGLE UP " + e.getAction(), Toast.LENGTH_SHORT).show(); 

        return false; 

    } 

 

    @Override 

    public boolean onScroll(MotionEvent e1, MotionEvent e2, 

            float distanceX, float distanceY) { 

        Toast.makeText(mContext, "SCROLL " + e2.getAction(), Toast.LENGTH_SHORT).show(); 

        return false; 

    } 

 

    @Override 

    public void onLongPress(MotionEvent e) { 

        Toast.makeText(mContext, "LONG " + e.getAction(), Toast.LENGTH_SHORT).show(); 

    } 

 

    @Override 

    public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, 

            float velocityY) { 

        Toast.makeText(mContext, "FLING " + e2.getAction(), Toast.LENGTH_SHORT).show(); 

        return false; 

    } 

 

    @Override 

    public boolean onDoubleTap(MotionEvent e) { 

        Toast.makeText(mContext, "DOUBLE " + e.getAction(), Toast.LENGTH_SHORT).show(); 

        return false; 

    } 

 

    @Override 

    public boolean onDoubleTapEvent(MotionEvent e) { 

        Toast.makeText(mContext, "DOUBLE EVENT " + e.getAction(), Toast.LENGTH_SHORT).show(); 

        return false; 

    } 

 

    @Override 

    public boolean onSingleTapConfirmed(MotionEvent e) { 

        Toast.makeText(mContext, "SINGLE CONF " + e.getAction(), Toast.LENGTH_SHORT).show(); 

        return false; 

    } 

} 

 

 

我們可以在Activity裡設置手勢識別：

import android.app.Activity; 

import android.os.Bundle; 

import android.view.GestureDetector; 

import android.view.MotionEvent; 

 

public class GestureTestActivity extends Activity { 

    private GestureDetector mGestureDetector; 

 

    @Override 

    public void onCreate(Bundle savedInstanceState) { 

        super.onCreate(savedInstanceState); 

        setContentView(R.layout.main); 

 

        mGestureDetector = new GestureDetector(this, new MyGestureListener(this)); 

    } 

 

    @Override 

    public boolean onTouchEvent(MotionEvent event) { 

        return mGestureDetector.onTouchEvent(event); 

    } 

} 

自定View中使用手勢識別

import android.content.Context; 

import android.util.AttributeSet; 

import android.view.GestureDetector; 

import android.view.MotionEvent; 

import android.view.View; 

 

public class MyView extends View { 

 

    private GestureDetector mGestureDetector; 

 

    public MyView(Context context, AttributeSet attrs) { 

        super(context, attrs); 

 

        mGestureDetector = new GestureDetector(context, new MyGestureListener(context)); 

 

        setLongClickable(true); 

 

        this.setOnTouchListener(new OnTouchListener() { 

 

            public boolean onTouch(View v, MotionEvent event) { 

                return mGestureDetector.onTouchEvent(event); 

            } 

 

        }); 

    } 

} 

 

需要注意的問題：

對於自定義View，使用手勢識別有兩處陷阱可能會浪費你的不少時間。

1：View必須設置longClickable為true，否則手勢識別無法正確工作，只會返回Down, Show, Long三種手勢

2：必須在View的onTouchListener中調用手勢識別，而不能像Activity一樣重載onTouchEvent，否則同樣手勢識別無法正確工作


測試結果


下面是各種操作返回的手勢序列，數值0表示觸摸屏按下，1表示抬起

單擊：down 0, single up 1, single conf 0


短按：down 0, show 0, single up 1


長按：down 0, show 0, long 0


雙擊：down 0, single up 1, double 0, double event 0, down 0, double event 1


滾動：down 0, (show 0), scrool 2...


滑動：down 0, (show 0), scrool 2..., fling 1

手勢滑動在播放器中的應用

我們可以通過手勢的滑動來調節音量，來控制進度。

package com.kankan.anime.player;

import android.app.Activity;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;

import com.kankan.anime.R;
import com.kankan.anime.player.GestureDetector.SimpleOnGestureListener;
import com.kankan.anime.player.local.LocalPlayerActivity;
import com.kankan.anime.util.NetworkHelper;
import com.kankan.anime.util.UIHelper;
import com.kankan.anime.widget.MediaController;
import com.kankan.anime.widget.MediaController.MediaPlayerControl;
import com.kankan.anime.widget.VideoGestureSeekWidget;
import com.kankan.anime.widget.VoiceLightWidget;
import com.kankan.logging.Logger;

public class GestureDelegator {
    private static final Logger LOG = Logger.getLogger(GestureDelegator.class);

    private static final double RADIUS_SLOP = Math.PI * 5 / 24;

    private static final int GESTURE_NONE = 0;
    private static final int GESTURE_VOICE = GESTURE_NONE + 1;
    private static final int GESTURE_LIGHT = GESTURE_VOICE + 1;
    private static final int GESTURE_PROGRESS = GESTURE_LIGHT + 1;
    private static final int MAX_SEEK_TIME = (int) (1.5 * 60);// 屏幕滑動快進，滑動一屏幕是180s

    private VoiceLightWidget mVoiceLightWidget;
    private VideoGestureSeekWidget mSeekWidget;
    private int mCurrentGesture;
    private final MediaController mMediaController;
    private final GestureDetector mGestureDetector;
    private final MediaController.MediaPlayerControl mPlayerController;
    private final Activity mContext;
    private Fragment mFragment;

    private int mDragPos;
    private int mCurrentDeltaScroll;
    private int mScrolledPixPerVideoSecend;
    private int mDeltaAll = 0;
    private boolean mNeedResume;

    public GestureDelegator(Fragment fragment, MediaController mediaController,
            MediaPlayerControl mediaPlayerControl) {
        mMediaController = mediaController;
        mFragment = fragment;
        mContext = fragment.getActivity();
        mPlayerController = mediaPlayerControl;
        mScrolledPixPerVideoSecend = (int) (UIHelper.getScreenWidth(mContext) * 0.7) / MAX_SEEK_TIME;

        mGestureDetector = new GestureDetector(mContext, mGestureListener);

        attachVoiceControllerToActivity();
    }

    private void clearDragPos() {
        mDragPos = 0;
        mDeltaAll = 0;
    }

    public boolean onTouchEvent(MotionEvent ev) {
        if (mMediaController.isShowing() && (mMediaController.isActionInPannel(ev) && !mMediaController.isLocked())) {
            mMediaController.show();

            return true;
        }

        final int action = ev.getAction();
        if (action == MotionEvent.ACTION_UP
                || action == MotionEvent.ACTION_CANCEL) {
            if (mCurrentGesture == GESTURE_PROGRESS) {
                if (mNeedResume) {
                    mPlayerController.start();
                    mNeedResume = !mNeedResume;
                }

                mPlayerController.seekTo(mDragPos);

                clearDragPos();
            }

            if (mCurrentGesture == GESTURE_NONE) {
                if (mMediaController.isLocked()) {
                    if (!mMediaController.isShowing()) {
                        mMediaController.show();
                    } else {
                        mMediaController.hide();
                    }
                } else {
                    if (!mMediaController.isShowing()) {
                        mMediaController.show();
                        mMediaController.showSystemUI();
                    } else {
                        mMediaController.hide();
                        mMediaController.hideSystemUI();
                    }
                }
            }

            if (mMediaController.isShowing() && mCurrentGesture != GESTURE_NONE) {
                mMediaController.fadeOut(1000);
            }
            mCurrentGesture = GESTURE_NONE;
        }

        if (action == MotionEvent.ACTION_MOVE) {
            if (mMediaController.isShowing()) {
                mMediaController.show();
            }
        }
        if (!mMediaController.isLocked()) {
            mGestureDetector.onTouchEvent(ev);
        }

        return true;
    }

    private void attachVoiceControllerToActivity() {
        ViewGroup outFrame = (ViewGroup) mFragment.getView();
        View layer = LayoutInflater.from(mContext).inflate(R.layout.gesture_widget_layer, null);
        mVoiceLightWidget = (VoiceLightWidget) layer.findViewById(R.id.voice_controller);
        mSeekWidget = (VideoGestureSeekWidget) layer.findViewById(R.id.video_seek_controller);
        if (outFrame != null) {
            outFrame.addView(layer);
        }
    }

    private SimpleOnGestureListener mGestureListener = new SimpleOnGestureListener() {

        public boolean onDoubleTap(MotionEvent e) {
            if (mPlayerController.isPlaying()) {
                mPlayerController.pause();
            } else {
                if (mContext instanceof LocalPlayerActivity) {
                    mPlayerController.start();
                } else {
                    NetworkHelper.getInstance().accessNetwork(mContext, new Runnable() {

                        @Override
                        public void run() {
                            mPlayerController.start();
                        }
                    });
                }
            }
            return true;
        };

        public boolean onScroll(MotionEvent e1, MotionEvent e2,
                float distanceX, float distanceY) {
            if (e1 == null || e2 == null) {
                return false;
            }
            float oldX = e1.getX();
            final double distance = Math.sqrt(Math.pow(distanceX, 2)
                    + Math.pow(distanceY, 2));
            int windowWidth = UIHelper.getScreenWidth(mContext);
            final double radius = distanceY / distance;

            if (Math.abs(radius) > RADIUS_SLOP) {
                if (mCurrentGesture != GESTURE_PROGRESS
                        && !mSeekWidget.isVisiable()) {
                    if (oldX > windowWidth / 2) {// TODO右半屏幕處理聲音的邏輯
                        mCurrentGesture = GESTURE_VOICE;
                        onVoiceChange(distanceY, distance);
                    } else {// TODO左半屏幕處理亮度的邏輯
                        mCurrentGesture = GESTURE_LIGHT;
                        onLightChange(distanceY, distance);
                    }
                }
            } else {// TODO 處理視頻進度
                if (mCurrentGesture != GESTURE_VOICE
                        && mCurrentGesture != GESTURE_LIGHT
                        && !mVoiceLightWidget.isVisible()) {
                    onVideoTouchSeek(distanceX, distance);
                }
            }

            return super.onScroll(e1, e2, distanceX, distanceY);
        }
    };

    private void onVoiceChange(float delta, double distance) {
        mSeekWidget.setVisibility(View.GONE);
        mVoiceLightWidget.onVoiceChange(delta, (int) distance);
    }

    private void onLightChange(float delta, double distance) {
        mSeekWidget.setVisibility(View.GONE);
        mVoiceLightWidget.onLightChange(delta, (int) distance,
                mContext.getWindow());
    }

    private void onVideoTouchSeek(float distanceX, double distane) {
        mVoiceLightWidget.setVisibility(View.GONE);

        if (mDragPos == 0 && mCurrentGesture != GESTURE_PROGRESS) {
            mDragPos = mPlayerController.getCurrentPosition();
        }

        if (mPlayerController.isPlaying()) {
            mPlayerController.pause();
            mNeedResume = true;
        }

        mCurrentGesture = GESTURE_PROGRESS;

        mCurrentDeltaScroll += distanceX;
        
        if (Math.abs(mCurrentDeltaScroll) >= mScrolledPixPerVideoSecend) {
            int deltaTime = mCurrentDeltaScroll / mScrolledPixPerVideoSecend;
            mDeltaAll += deltaTime;
            mDragPos = mDragPos - deltaTime * 1000;
            if (mDragPos > mPlayerController.getDuration()) {
                mDragPos = mPlayerController.getDuration();
            }
            if (mDragPos < 0) {
                mDragPos = 0;
                mDeltaAll = 0;
            }

            mCurrentDeltaScroll = 0;
        }

        mSeekWidget.onSeek(mDragPos, mPlayerController.getDuration(), mDeltaAll);
    }
}

最後我們附上

GestureDetector.java文件

package com.kankan.anime.player;

/*
 * 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.
 */

import android.content.Context;
import android.os.Handler;
import android.os.Message;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;

import com.kankan.logging.Logger;

/**
 * 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:
 * 

 * 
Create an instance of the {@code GestureDetector} for your {@link View}
 * 
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.
 * 
 */
public class GestureDetector {
    @SuppressWarnings("unused")
    private static final Logger LOG = Logger.getLogger(GestureDetector.class);

    /**
     * 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.
         * 

         * 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;
        }
    }

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

    /**
     * 解決huawei meit手動隱藏navigationBar導致 doubleTab失效問題
     */
    private float mDoubleTapSlopSquareFactor = 1.3f;

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

    private boolean mIsLongpressEnabled;

    /**
     * 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) {
        if (handler != null) {
            mHandler = new GestureHandler(handler);
        } else {
            mHandler = new GestureHandler();
        }
        mListener = listener;
        if (listener instanceof OnDoubleTapListener) {
            setOnDoubleTapListener((OnDoubleTapListener) listener);
        }
        init(context);
    }

    /**
     * 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,
            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;
        final ViewConfiguration configuration = ViewConfiguration.get(context);
        touchSlop = configuration.getScaledTouchSlop();
        // doubleTapTouchSlop = configuration.getScaledDoubleTapTouchSlop();
        doubleTapTouchSlop = configuration.getScaledTouchSlop();
        doubleTapSlop = configuration.getScaledDoubleTapSlop();
        mMinimumFlingVelocity = configuration.getScaledMinimumFlingVelocity();
        mMaximumFlingVelocity = configuration.getScaledMaximumFlingVelocity();
        mTouchSlopSquare = touchSlop * touchSlop;
        mDoubleTapTouchSlopSquare = doubleTapTouchSlop * doubleTapTouchSlop;
        // mDoubleTapSlopSquare = doubleTapSlop * doubleTapSlop;
        mDoubleTapSlopSquare = (int) (doubleTapSlop * doubleTapSlop * mDoubleTapSlopSquareFactor);
    }

    /**
     * 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();

        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;

        // 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;
                    // 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;

            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) {
                break;
            }
            final float scrollX = mLastFocusX - focusX;
            final float scrollY = mLastFocusY - focusY;

            if (mIsDoubleTapping) {
                // Give the move events of the 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);
                if (distance > mTouchSlopSquare) {
                    handled = mListener.onScroll(mCurrentDownEvent, ev, scrollX, scrollY);
                    mLastFocusX = focusX;
                    mLastFocusY = focusY;
                    mAlwaysInTapRegion = false;
                    mHandler.removeMessages(TAP);
                    mHandler.removeMessages(SHOW_PRESS);
                    mHandler.removeMessages(LONG_PRESS);
                }
                if (distance > mDoubleTapTouchSlopSquare) {
                    mAlwaysInBiggerTapRegion = false;
                }
            } else if ((Math.abs(scrollX) >= 1) || (Math.abs(scrollY) >= 1)) {
                handled = mListener.onScroll(mCurrentDownEvent, ev, scrollX, scrollY);
                mLastFocusX = focusX;
                mLastFocusY = focusY;
            }

            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;
                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;
            mHandler.removeMessages(SHOW_PRESS);
            mHandler.removeMessages(LONG_PRESS);
            break;

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

        return handled;
    }

    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;
        if (mInLongPress) {
            mInLongPress = false;
        }
    }

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

好，Android的手勢識別就到這裡。謝謝。