Reactor这个词译成汉语还真没有什么合适的，很多地方叫反应器模式，但更多好像就直接叫reactor模式了，其实我觉着叫应答者模式更好理解一些。通过了解，这个模式更像一个侍卫，一直在等待你的召唤，或者叫召唤兽。

并发系统常使用reactor模式，代替常用的多线程的处理方式，节省系统的资源，提高系统的吞吐量。

先用比较直观的方式来介绍一下这种方式的优点，通过和常用的多线程方式比较一下，可能更好理解。

以一个餐饮为例，每一个人来就餐就是一个事件，他会先看一下菜单，然后点餐。就像一个网站会有很多的请求，要求服务器做一些事情。处理这些就餐事件的就需要我们的服务人员了。

在多线程处理的方式会是这样的：

一个人来就餐，一个服务员去服务，然后客人会看菜单，点菜。 服务员将菜单给后厨。

二个人来就餐，二个服务员去服务……

五个人来就餐，五个服务员去服务……

这个就是多线程的处理方式，一个事件到来，就会有一个线程服务。很显然这种方式在人少的情况下会有很好的用户体验，每个客人都感觉自己是VIP，专人服务的。如果餐厅一直这样同一时间最多来5个客人，这家餐厅是可以很好的服务下去的。

来了一个好消息，因为这家店的服务好，吃饭的人多了起来。同一时间会来10个客人，老板很开心，但是只有5个服务员，这样就不能一对一服务了，有些客人就要没有人管了。老板就又请了5个服务员，现在好了，又能每个人都受VIP待遇了。

越来越多的人对这家餐厅满意，客源又多了，同时来吃饭的人到了20人，老板高兴不起来了，再请服务员吧，占地方不说，还要开工钱，再请人就攒不到钱了。怎么办呢？老板想了想，10个服务员对付20个客人也是能对付过来的，服务员勤快点就好了，伺候完一个客人马上伺候另外一个，还是来得及的。综合考虑了一下，老板决定就使用10个服务人员的线程池啦~~~

但是这样有一个比较严重的缺点就是，如果正在接受服务员服务的客人点菜很慢，其他的客人可能就要等好长时间了。有些火爆脾气的客人可能就等不了走人了。

Reactor如何处理这个问题呢：

老板后来发现，客人点菜比较慢，大部服务员都在等着客人点菜，其实干的活不是太多。老板能当老板当然有点不一样的地方，终于发现了一个新的方法，那就是：当客人点菜的时候，服务员就可以去招呼其他客人了，等客人点好了菜，直接招呼一声“服务员”，马上就有个服务员过去服务。嘿嘿，然后在老板有了这个新的方法之后，就进行了一次裁员，只留了一个服务员！这就是用单个线程来做多线程的事。

实际的餐馆都是用的Reactor模式在服务。一些设计的模型其实都是从生活中来的。

Reactor模式主要是提高系统的吞吐量，在有限的资源下处理更多的事情。

在单核的机上，多线程并不能提高系统的性能，除非在有一些阻塞的情况发生。否则线程切换的开销会使处理的速度变慢。就像你一个人做两件事情，1、削一个苹果。2、切一个西瓜。那你可以一件一件的做，我想你也会一件一件的做。如果这个时候你使用多线程，一会儿削苹果，一会切西瓜，可以相像究竟是哪个速度快。这也就是说为什么在单核机上多线程来处理可能会更慢。

但当有阻碍操作发生时，多线程的优势才会显示出来，现在你有另外两件事情去做，1、削一个苹果。2、烧一壶开水。我想没有人会去做完一件再做另一件，你肯定会一边烧水，一边就把苹果削了。

Source: http://daimojingdeyu.iteye.com/blog/828696

转载博客,相当感谢博主

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package com.xiaxing.slidingdrawer;

import java.util.ArrayList;

import android.content.Context;
import android.util.Log;
import android.view.KeyEvent;
import android.view.LayoutInflater;
import android.view.MotionEvent;
import android.view.SurfaceView;
import android.view.View;
import android.view.ViewGroup;
import android.view.animation.Animation;
import android.view.animation.TranslateAnimation;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.FrameLayout;
import android.widget.ListView;
import android.widget.TextView;

import com.xiaxing.slidingdrawer.R;

public class LeftListView implements View.OnClickListener {
    public static final int DIRECTION_LEFT = 0;
    public static final int DIRECTION_RIGHT = 1;
    public static final int DIRECTION_UP = 2;
    public static final int DIRECTION_DOWN = 3;

    private static final String TAG = "xiaxing";
    private Context mContext;
    private final LayoutInflater mInflater;

    private ListView mAchivementList;
    private ListView mFriendList;

    private AchivementAdapter mAchivementAdapter;
    private FriendAdapter mFriendAdapter;

    private boolean mIsVisible = true;

    private Button mAchivementBtn;
    private Button mFriendBtn;

    private boolean mIsFriendListVisable = false;
    
    private FrameLayout mContainer;

    public interface OnVisibilityChangedListener {
        public void onVisibilityChanged(boolean visbility);
    }

    public LeftListView(Context context, FrameLayout rootView) {
        mContext = context;
        mInflater = (LayoutInflater)mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        mContainer = rootView;
        if (this.mContainer == null) 
            Log.e("xiaxing", "mContainer is null");
        mInflater.inflate(R.layout.anyclock_layout_achivement_list, mContainer);
        mFriendList = (ListView)(mContainer.findViewById(R.id.friend_view));
        mAchivementList = (ListView)(mContainer.findViewById(R.id.achivement_view));
        mAchivementBtn = (Button)(mContainer.findViewById(R.id.btn_achivement));
        mAchivementBtn.setOnClickListener(this);
        mFriendBtn = (Button)(mContainer.findViewById(R.id.btn_friend));
        mFriendBtn.setOnClickListener(this);
    }

    public boolean isVisible() {
        return mIsVisible;
    }

    public void testPreference() {
        ArrayList<String> list = new ArrayList<String>();

        for (int i = 0, n = 10; i < n; ++i) {
            list.add("item");
        }

        mFriendAdapter = new FriendAdapter(mContext, list);
        mFriendList.setAdapter(mFriendAdapter);
        mFriendList.setOnItemClickListener(mFriendAdapter);

        mAchivementAdapter = new AchivementAdapter(mContext, list);
        mAchivementList.setAdapter(mAchivementAdapter);
        mAchivementList.setOnItemClickListener(mAchivementAdapter);

    }
    
    public void processTouchEvent(MotionEvent event) {
        Log.v(TAG, "LeftListView onTouch");
//        mContainer.onTouchEvent(event);
        this.mContainer.dispatchTouchEvent(event);
    }

    private class FriendAdapter extends BaseAdapter
            implements OnItemClickListener {
        private final ArrayList<String> mPreferences;

        public FriendAdapter(Context context, ArrayList<String> preferences) {
            mPreferences = preferences;
        }

        public void onItemClick(
                AdapterView<?> parent, View view, int position, long id) {
            // Preference preference = mPreferences.get(position);
            // TODO::
            Log.v(TAG, "MainMenuAdapter -- " + "onItemClick :  " + position);

        }

        public View getView(int position, View convertView, ViewGroup parent) {

            convertView = inflateIfNeed(convertView, R.layout.anyclock_content_achivement_item, parent, false);

            TextView musictime = (TextView)convertView.findViewById(R.id.grid_music_time);
            musictime.setText("20120000");

            TextView musicname = (TextView)convertView.findViewById(R.id.grid_music_name);
            musicname.setText("好友名称");

            TextView artist = (TextView)convertView.findViewById(R.id.grid_music_artist);
            artist.setText("你是我的好友吗");

            return convertView;
        }

        @Override
        public boolean areAllItemsEnabled() {
            return false;
        }

        // @Override
        // public boolean isEnabled(int position) {
        // Preference preference = mPreferences.get(position);
        // return !(preference instanceof PreferenceGroup);
        // }

        public int getCount() {
            return mPreferences.size();
        }

        public Object getItem(int position) {
            return null;
        }

        public long getItemId(int position) {
            return position;
        }

        // @Override
        // public int getItemViewType(int position) {
        // Preference pref = mPreferences.get(position);
        // if (pref instanceof PreferenceGroup)
        // return 0;
        // if (pref instanceof ListPreference)
        // return 1;
        // throw new IllegalStateException();
        // }

        @Override
        public int getViewTypeCount() {
            // we have two types, see getItemViewType()
            return 2;
        }

        @Override
        public boolean hasStableIds() {
            return true;
        }

        @Override
        public boolean isEmpty() {
            return mPreferences.isEmpty();
        }
    }

    private class AchivementAdapter extends BaseAdapter
            implements OnItemClickListener {
        private final ArrayList<String> mPreferences;

        public AchivementAdapter(Context context, ArrayList<String> preferences) {
            mPreferences = preferences;
        }

        public void onItemClick(
                AdapterView<?> parent, View view, int position, long id) {
            // Preference preference = mPreferences.get(position);
            // TODO::
            Log.v(TAG, "MainMenuAdapter -- " + "onItemClick :  " + position);

        }

        public View getView(int position, View convertView, ViewGroup parent) {

            convertView = inflateIfNeed(convertView, R.layout.anyclock_content_achivement_item, parent, false);

            TextView musictime = (TextView)convertView.findViewById(R.id.grid_music_time);
            musictime.setText("20120000");

            TextView musicname = (TextView)convertView.findViewById(R.id.grid_music_name);
            musicname.setText("成就名称");

            TextView artist = (TextView)convertView.findViewById(R.id.grid_music_artist);
            artist.setText("成就说明：早起的鸟儿啊？？？");

            return convertView;
        }

        @Override
        public boolean areAllItemsEnabled() {
            return false;
        }

        // @Override
        // public boolean isEnabled(int position) {
        // Preference preference = mPreferences.get(position);
        // return !(preference instanceof PreferenceGroup);
        // }

        public int getCount() {
            return mPreferences.size();
        }

        public Object getItem(int position) {
            return null;
        }

        public long getItemId(int position) {
            return position;
        }

        // @Override
        // public int getItemViewType(int position) {
        // Preference pref = mPreferences.get(position);
        // if (pref instanceof PreferenceGroup)
        // return 0;
        // if (pref instanceof ListPreference)
        // return 1;
        // throw new IllegalStateException();
        // }

        @Override
        public int getViewTypeCount() {
            // we have two types, see getItemViewType()
            return 2;
        }

        @Override
        public boolean hasStableIds() {
            return true;
        }

        @Override
        public boolean isEmpty() {
            return mPreferences.isEmpty();
        }
    }

    private View inflateIfNeed(
            View view, int resource, ViewGroup root, boolean attachToRoot) {
        if (view != null)
            return view;
        return mInflater.inflate(resource, root, attachToRoot);
    }

    public static Animation slideOut(View view, int to) {
        view.setVisibility(View.INVISIBLE);
        Animation anim;
        switch (to) {
            case DIRECTION_LEFT:
                anim = new TranslateAnimation(0, -view.getWidth() + 20, 0, 0);
                break;
            case DIRECTION_RIGHT:
                anim = new TranslateAnimation(0, view.getWidth(), 0, 0);
                break;
            case DIRECTION_UP:
                anim = new TranslateAnimation(0, 0, 0, -view.getHeight());
                break;
            case DIRECTION_DOWN:
                anim = new TranslateAnimation(0, 0, 0, view.getHeight());
                break;
            default:
                throw new IllegalArgumentException(Integer.toString(to));
        }
        anim.setDuration(500);
        view.startAnimation(anim);
        return anim;
    }

    public static Animation slideIn(View view, int from) {
        view.setVisibility(View.VISIBLE);
        Animation anim;
        switch (from) {
            case DIRECTION_LEFT:
                anim = new TranslateAnimation(-view.getWidth(), 0, 0, 0);
                break;
            case DIRECTION_RIGHT:
                anim = new TranslateAnimation(view.getWidth(), 0, 0, 0);
                break;
            case DIRECTION_UP:
                anim = new TranslateAnimation(0, 0, -view.getHeight(), 0);
                break;
            case DIRECTION_DOWN:
                anim = new TranslateAnimation(0, 0, view.getHeight(), 0);
                break;
            default:
                throw new IllegalArgumentException(Integer.toString(from));
        }
        anim.setDuration(500);
        view.startAnimation(anim);
        return anim;
    }

    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub
        if (v.equals(mFriendBtn)) {
            Log.v(TAG, "mAchivementBtn clicked");
            slideIn(mFriendList, DIRECTION_RIGHT);
            mIsFriendListVisable = true;
        } else if (v.equals(mAchivementBtn)) {
            if (mIsFriendListVisable) {
                slideOut(mFriendList, DIRECTION_RIGHT);
                mIsFriendListVisable = false;
            }
            Log.v(TAG, "mFriendBtn clicked");
        }
    }
}

package com.xiaxing.slidingdrawer;

import com.xiaxing.slidingdrawer.R;

import android.os.Bundle;
import android.app.Activity;
import android.util.Log;
import android.view.GestureDetector;
import android.view.Menu;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.View.OnTouchListener;
import android.widget.FrameLayout;
import android.widget.ImageView;

public class MainActivity extends Activity implements OnClickListener, OnTouchListener {
    private LeftListView mAchivementList;
    private ImageView mGripBtn;
    private View mListView;
    private boolean mIsListViewVisale = false;

    private GestureDetector mGestureDetector;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main_activity);
        findViewById(R.id.viewtag).setOnTouchListener(this);
    }

    @SuppressWarnings("deprecation")
    @Override
    public void onStart() {
        super.onStart();
        showAchivementList();
        mGestureDetector = new GestureDetector(new MyGestureListener());
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }

    public void showAchivementList() {
        if (mAchivementList == null) {
            FrameLayout fl = (FrameLayout)findViewById(R.id.mainview);
            mAchivementList = new LeftListView(this, fl);
            mAchivementList.testPreference();
        }
    }

    @Override
    public void onClick(View view) {
        // TODO Auto-generated method stub
        if (view.getId() == mGripBtn.getId()) {
            Log.v("xiaxing", "main activity onClick");
            if (mIsListViewVisale) {
                LeftListView.slideIn(mListView, LeftListView.DIRECTION_LEFT);
                mIsListViewVisale = false;
            } else {
                LeftListView.slideOut(mListView, LeftListView.DIRECTION_LEFT);
                mIsListViewVisale = true;
            }
        }
    }
    
    @Override
    public boolean onTouch(View v, MotionEvent event) {
        mAchivementList.processTouchEvent(event);
        return mGestureDetector.onTouchEvent(event);
    }

    
    private int verticalMinDistance = 120;
    private int minVelocity = 0;

    private class MyGestureListener extends GestureDetector.SimpleOnGestureListener {

        @Override
        public boolean onDown(MotionEvent arg0) {
            // TODO Auto-generated method stub
//            Log.v("xiaxing", "onDown 1");
//            if (mIsListViewVisale)
//                return true;
//            else
//                return false;
            
            return true;
        }

        public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
            Log.v("xiaxing", "onFling");
            if (e1.getX() - e2.getX() > verticalMinDistance && Math.abs(velocityX) > minVelocity) {
                Log.v("xiaxing", "onFling 2");
                if (!mIsListViewVisale) {
                    LeftListView.slideOut(mListView, LeftListView.DIRECTION_LEFT);
                    mIsListViewVisale = false;    
                }
                
            } else if (e2.getX() - e1.getX() > verticalMinDistance && Math.abs(velocityX) > minVelocity) {
                Log.v("xiaxing", "onFling 1");
                if (mIsListViewVisale) {
                    LeftListView.slideIn(mListView, LeftListView.DIRECTION_LEFT);
                    mIsListViewVisale = false;
                }
            }
            
            return true;
            
        }

        @Override
        public void onLongPress(MotionEvent arg0) {
            // TODO Auto-generated method stub
            Log.v("xiaxing", "onLongPress 2");

        }

        @Override
        public boolean onScroll(MotionEvent arg0, MotionEvent arg1, float arg2, float arg3) {
            // TODO Auto-generated method stub
            Log.v("xiaxing", "onScroll 1");
            return true;
        }

        @Override
        public void onShowPress(MotionEvent arg0) {
            // TODO Auto-generated method stub
            Log.v("xiaxing", "onShowPress 2");

        }

        @Override
        public boolean onSingleTapUp(MotionEvent arg0) {
            // TODO Auto-generated method stub
            Log.v("xiaxing", "onSingleTapUp 2");
            return true;
        }
    }

}

package com.xiaxing.slidingdrawer;

import android.view.View;
import android.view.animation.Animation;
import android.view.animation.TranslateAnimation;

public class Util {
    private static final String TAG = "Util";
    public static final int DIRECTION_LEFT = 0;
    public static final int DIRECTION_RIGHT = 1;
    public static final int DIRECTION_UP = 2;
    public static final int DIRECTION_DOWN = 3;
    
    public static Animation slideOut(View view, int to) {
        view.setVisibility(View.INVISIBLE);
        Animation anim;
        switch (to) {
            case DIRECTION_LEFT:
                anim = new TranslateAnimation(0, -view.getWidth(), 0, 0);
                break;
            case DIRECTION_RIGHT:
                anim = new TranslateAnimation(0, view.getWidth(), 0, 0);
                break;
            case DIRECTION_UP:
                anim = new TranslateAnimation(0, 0, 0, -view.getHeight());
                break;
            case DIRECTION_DOWN:
                anim = new TranslateAnimation(0, 0, 0, view.getHeight());
                break;
            default:
                throw new IllegalArgumentException(Integer.toString(to));
        }
        anim.setDuration(500);
        view.startAnimation(anim);
        return anim;
    }

    public static Animation slideIn(View view, int from) {
        view.setVisibility(View.VISIBLE);
        Animation anim;
        switch (from) {
            case DIRECTION_LEFT:
                anim = new TranslateAnimation(-view.getWidth(), 0, 0, 0);
                break;
            case DIRECTION_RIGHT:
                anim = new TranslateAnimation(view.getWidth(), 0, 0, 0);
                break;
            case DIRECTION_UP:
                anim = new TranslateAnimation(0, 0, -view.getHeight(), 0);
                break;
            case DIRECTION_DOWN:
                anim = new TranslateAnimation(0, 0, view.getHeight(), 0);
                break;
            default:
                throw new IllegalArgumentException(Integer.toString(from));
        }
        anim.setDuration(500);
        view.startAnimation(anim);
        return anim;
    }
    
    public static boolean equals(Object a, Object b) {
        return (a == b) || (a == null ? false : a.equals(b));
    }
    
    public static <T> T checkNotNull(T object) {
        if (object == null) throw new NullPointerException();
        return object;
    }
}

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/main_layout"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:background="@android:color/black" >

    <RelativeLayout
        android:id="@+id/main_panel"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:layout_toLeftOf="@+id/btn_gripper_hide"
        android:background="#ffffff00" >

        <FrameLayout
            android:id="@+id/list_view"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:layout_marginLeft="10dp"
            android:layout_marginRight="10dp"
            android:layout_toEndOf="@+id/btn_list"
            android:background="@android:color/black" >

            <ListView
                android:id="@+id/friend_view"
                android:layout_width="fill_parent"
                android:layout_height="fill_parent" />

            <ListView
                android:id="@+id/achivement_view"
                android:layout_width="fill_parent"
                android:layout_height="fill_parent" />
        </FrameLayout>

        <LinearLayout
            android:id="@+id/btn_list"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_alignParentBottom="true"
            android:background="@android:color/black"
            android:orientation="horizontal" >

            <Button
                android:id="@+id/btn_achivement"
                android:layout_width="fill_parent"
                android:layout_height="fill_parent"
                android:layout_weight="1"
                android:text="成就" />

            <Button
                android:id="@+id/btn_friend"
                android:layout_width="fill_parent"
                android:layout_height="fill_parent"
                android:layout_weight="1"
                android:text="好友" />

            <Button
                android:id="@+id/btn_more"
                android:layout_width="fill_parent"
                android:layout_height="fill_parent"
                android:layout_weight="1"
                android:text="更多" />
        </LinearLayout>
    </RelativeLayout>

    <ImageView
        android:id="@+id/btn_gripper_hide"
        android:layout_width="20dp"
        android:layout_height="fill_parent"
        android:layout_alignParentRight="true" />

    <ImageView
        android:id="@+id/touch_mask"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:layout_alignParentRight="true" />

</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal"
    android:paddingTop="0dip"
    android:background="@android:color/black" >

    <FrameLayout
        android:layout_width="70dip"
        android:layout_height="70dip"
        android:layout_gravity="left"
        android:gravity="right"
        android:paddingBottom="5dip"
        android:paddingLeft="5dip"
        android:paddingRight="5dip"
        android:paddingTop="5dip" >

        <ImageView
            android:id="@+id/grid_item_img"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_gravity="center"
            android:scaleType="centerCrop"
            android:src="/blog_article/@drawable/anyshare_content_music_grid_item_bg/index.html" />

        <ImageView
            android:id="@+id/grid_item_shared"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_gravity="center"
            android:background="#77e0e0e0"
            android:visibility="invisible" />
    </FrameLayout>

    <FrameLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_gravity="left|center_vertical"
        android:gravity="left|center_vertical" >

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_gravity="left|center_vertical"
            android:layout_marginRight="40dip"
            android:gravity="left|center_vertical"
            android:orientation="vertical" >

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:orientation="horizontal" >

                <TextView
                    android:id="@+id/grid_music_name"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_marginTop="0dip"
                    android:layout_weight="1"
                    android:gravity="left|center_vertical"
                    android:singleLine="true"
                    android:textColor="#ff7c7c7c"
                    android:textSize="18sp" />

                <TextView
                    android:id="@+id/grid_music_time"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_gravity="right|center_vertical"
                    android:layout_weight="0"
                    android:gravity="right"
                    android:singleLine="true"
                    android:textColor="#ff7c7c7c"
                    android:textSize="13sp" />
            </LinearLayout>

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:orientation="horizontal" >

                <TextView
                    android:id="@+id/grid_music_artist"
                    android:layout_width="0dip"
                    android:layout_height="wrap_content"
                    android:layout_gravity="left|center_vertical"
                    android:layout_weight="1"
                    android:gravity="left"
                    android:singleLine="true"
                    android:maxLines="2"
                    android:textColor="#ff7c7c7c"
                    android:textSize="13sp" />
            </LinearLayout>
        </LinearLayout>

        <ImageView
            android:id="@+id/grid_item_check"
            android:layout_width="30dip"
            android:layout_height="30dip"
            android:layout_gravity="right|center_vertical"
            android:paddingBottom="0dip"
            android:paddingRight="10dip"
            android:src="/blog_article/@drawable/anyshare_photo_check_on/index.html" />
    </FrameLayout>

</LinearLayout>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/main_layout"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:background="@android:color/black" >

    <FrameLayout
        android:id="@+id/mainview"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" />

    <ImageView
        android:id="@+id/viewtag"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:layout_alignParentRight="true" />

</RelativeLayout>