android手机开发之网络多线程断点续传代码

RandomAccessFile threadfile = new RandomAccessFile("QQWubiSetup.exe ","rwd");

threadfile.seek(2097152);//从文件的什么位置开始写入数据

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string name="hello">Hello World, MainActivity!</string>
    <string name="app_name">Android网络多线程断点下载</string>
    <string name="path">下载路径</string>
    <string name="downloadbutton">下载</string>
    <string name="sdcarderror">SDCard不存在或者写保护</string>
    <string name="success">下载完成</string>
    <string name="error">下载失败</string>
</resources>

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"      package="com.android.downloader"      android:versionCode="1"      android:versionName="1.0">
    <uses-sdk android:minSdkVersion="8" />

    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".MainActivity"
                  android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

    </application>
   
    <!-- 在SDCard中创建与删除文件权限 -->
    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
   
    <!-- 往SDCard写入数据权限 -->
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
   
    <!-- 访问internet权限 -->
    <uses-permission android:name="android.permission.INTERNET"/>

</manifest> 

package com.android.downloader;
import java.io.File;

import com.android.network.DownloadProgressListener;
import com.android.network.FileDownloader;

import android.app.Activity;
import android.os.Bundle;
import android.os.Environment;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity {
    private EditText downloadpathText;
    private TextView resultView;
    private ProgressBar progressBar;
   
    /**
     * 当Handler被创建会关联到创建它的当前线程的消息队列，该类用于往消息队列发送消息
     * 消息队列中的消息由当前线程内部进行处理
     */
    private Handler handler = new Handler(){

        @Override
        public void handleMessage(Message msg) {           
            switch (msg.what) {
            case 1:               
                progressBar.setProgress(msg.getData().getInt("size"));
                float num = (float)progressBar.getProgress()/(float)progressBar.getMax();
                int result = (int)(num*100);
                resultView.setText(result+ "%");
               
                if(progressBar.getProgress()==progressBar.getMax()){
                    Toast.makeText(MainActivity.this, R.string.success, 1).show();
                }
                break;
            case -1:
                Toast.makeText(MainActivity.this, R.string.error, 1).show();
                break;
            }
        }
    };
   
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
       
        downloadpathText = (EditText) this.findViewById(R.id.path);
        progressBar = (ProgressBar) this.findViewById(R.id.downloadbar);
        resultView = (TextView) this.findViewById(R.id.resultView);
        Button button = (Button) this.findViewById(R.id.button);
       
        button.setOnClickListener(new View.OnClickListener() {
           
            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                String path = downloadpathText.getText().toString();
                System.out.println(Environment.getExternalStorageState()+"------"+Environment.MEDIA_MOUNTED);
               
                if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
                    download(path, Environment.getExternalStorageDirectory());
                }else{
                    Toast.makeText(MainActivity.this, R.string.sdcarderror, 1).show();
                }
            }
        });
    }
   
      /**
       * 主线程(UI线程)
       * 对于显示控件的界面更新只是由UI线程负责，如果是在非UI线程更新控件的属性值，更新后的显示界面不会反映到屏幕上
       * @param path
       * @param savedir
       */
    private void download(final String path, final File savedir) {
        new Thread(new Runnable() {           
            @Override
            public void run() {
                FileDownloader loader = new FileDownloader(MainActivity.this, path, savedir, 3);
                progressBar.setMax(loader.getFileSize());//设置进度条的最大刻度为文件的长度
               
                try {
                    loader.download(new DownloadProgressListener() {
                        @Override
                        public void onDownloadSize(int size) {//实时获知文件已经下载的数据长度
                            Message msg = new Message();
                            msg.what = 1;
                            msg.getData().putInt("size", size);
                            handler.sendMessage(msg);//发送消息
                        }
                    });
                } catch (Exception e) {
                    handler.obtainMessage(-1).sendToTarget();
                }
            }
        }).start();
    }
} 

package com.android.service;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DBOpenHelper extends SQLiteOpenHelper {
    private static final String DBNAME = "down.db";
    private static final int VERSION = 1;
   
    public DBOpenHelper(Context context) {
        super(context, DBNAME, null, VERSION);
    }
   
    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("CREATE TABLE IF NOT EXISTS filedownlog (id integer primary key autoincrement, downpath varchar(100), threadid INTEGER, downlength INTEGER)");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS filedownlog");
        onCreate(db);
    }
}

package com.android.service;
import java.util.HashMap;
import java.util.Map;

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

public class FileService {
    private DBOpenHelper openHelper;

    public FileService(Context context) {
        openHelper = new DBOpenHelper(context);
    }
   
    /**
     * 获取每条线程已经下载的文件长度
     * @param path
     * @return
     */
    public Map<Integer, Integer> getData(String path){
        SQLiteDatabase db = openHelper.getReadableDatabase();
        Cursor cursor = db.rawQuery("select threadid, downlength from filedownlog where downpath=?", new String[]{path});
        Map<Integer, Integer> data = new HashMap<Integer, Integer>();
       
        while(cursor.moveToNext()){
            data.put(cursor.getInt(0), cursor.getInt(1));
        }
       
        cursor.close();
        db.close();
        return data;
    }
   
    /**
     * 保存每条线程已经下载的文件长度
     * @param path
     * @param map
     */
    public void save(String path,  Map<Integer, Integer> map){//int threadid, int position
        SQLiteDatabase db = openHelper.getWritableDatabase();
        db.beginTransaction();
       
        try{
            for(Map.Entry<Integer, Integer> entry : map.entrySet()){
                db.execSQL("insert into filedownlog(downpath, threadid, downlength) values(?,?,?)",
                        new Object[]{path, entry.getKey(), entry.getValue()});
            }
            db.setTransactionSuccessful();
        }finally{
            db.endTransaction();
        }
       
        db.close();
    }
   
    /**
     * 实时更新每条线程已经下载的文件长度
     * @param path
     * @param map
     */
    public void update(String path, Map<Integer, Integer> map){
        SQLiteDatabase db = openHelper.getWritableDatabase();
        db.beginTransaction();
       
        try{
            for(Map.Entry<Integer, Integer> entry : map.entrySet()){
                db.execSQL("update filedownlog set downlength=? where downpath=? and threadid=?",
                        new Object[]{entry.getValue(), path, entry.getKey()});
            }
           
            db.setTransactionSuccessful();
        }finally{
            db.endTransaction();
        }
       
        db.close();
    }
   
    /**
     * 当文件下载完成后，删除对应的下载记录
     * @param path
     */
    public void delete(String path){
        SQLiteDatabase db = openHelper.getWritableDatabase();
        db.execSQL("delete from filedownlog where downpath=?", new Object[]{path});
        db.close();
    }
} 

DownloadProgressListener中代码：

package com.android.network;
public interface DownloadProgressListener {
    public void onDownloadSize(int size);
} 

package com.android.network;
import java.io.File;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import com.android.service.FileService;

import android.content.Context;
import android.util.Log;

public class FileDownloader {
    private static final String TAG = "FileDownloader";
    private Context context;
    private FileService fileService;   
   
    /* 已下载文件长度 */
    private int downloadSize = 0;
   
    /* 原始文件长度 */
    private int fileSize = 0;
   
    /* 线程数 */
    private DownloadThread[] threads;
   
    /* 本地保存文件 */
    private File saveFile;
   
    /* 缓存各线程下载的长度*/
    private Map<Integer, Integer> data = new ConcurrentHashMap<Integer, Integer>();
   
    /* 每条线程下载的长度 */
    private int block;
   
    /* 下载路径  */
    private String downloadUrl;
   
    /**
     * 获取线程数
     */
    public int getThreadSize() {
        return threads.length;
    }
   
    /**
     * 获取文件大小
     * @return
     */
    public int getFileSize() {
        return fileSize;
    }
   
    /**
     * 累计已下载大小
     * @param size
     */
    protected synchronized void append(int size) {
        downloadSize += size;
    }
   
    /**
     * 更新指定线程最后下载的位置
     * @param threadId 线程id
     * @param pos 最后下载的位置
     */
    protected synchronized void update(int threadId, int pos) {
        this.data.put(threadId, pos);
        this.fileService.update(this.downloadUrl, this.data);
    }
   
    /**
     * 构建文件下载器
     * @param downloadUrl 下载路径
     * @param fileSaveDir 文件保存目录
     * @param threadNum 下载线程数
     */
    public FileDownloader(Context context, String downloadUrl, File fileSaveDir, int threadNum) {
        try {
            this.context = context;
            this.downloadUrl = downloadUrl;
            fileService = new FileService(this.context);
            URL url = new URL(this.downloadUrl);
            if(!fileSaveDir.exists()) fileSaveDir.mkdirs();
            this.threads = new DownloadThread[threadNum];                   
           
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setConnectTimeout(5*1000);
            conn.setRequestMethod("GET");
            conn.setRequestProperty("Accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*");
            conn.setRequestProperty("Accept-Language", "zh-CN");
            conn.setRequestProperty("Referer", downloadUrl);
            conn.setRequestProperty("Charset", "UTF-8");
            conn.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)");
            conn.setRequestProperty("Connection", "Keep-Alive");
            conn.connect();
            printResponseHeader(conn);
           
            if (conn.getResponseCode()==200) {
                this.fileSize = conn.getContentLength();//根据响应获取文件大小
                if (this.fileSize <= 0) throw new RuntimeException("Unkown file size ");
                       
                String filename = getFileName(conn);//获取文件名称
                this.saveFile = new File(fileSaveDir, filename);//构建保存文件
                Map<Integer, Integer> logdata = fileService.getData(downloadUrl);//获取下载记录
               
                if(logdata.size()>0){//如果存在下载记录
                    for(Map.Entry<Integer, Integer> entry : logdata.entrySet())
                        data.put(entry.getKey(), entry.getValue());//把各条线程已经下载的数据长度放入data中
                }
               
                if(this.data.size()==this.threads.length){//下面计算所有线程已经下载的数据长度
                    for (int i = 0; i < this.threads.length; i++) {
                        this.downloadSize += this.data.get(i+1);
                    }
                   
                    print("已经下载的长度"+ this.downloadSize);
                }
               
                //计算每条线程下载的数据长度
                this.block = (this.fileSize % this.threads.length)==0? this.fileSize / this.threads.length : this.fileSize / this.threads.length + 1;
            }else{
                throw new RuntimeException("server no response ");
            }
        } catch (Exception e) {
            print(e.toString());
            throw new RuntimeException("don't connection this url");
        }
    }
   
    /**
     * 获取文件名
     * @param conn
     * @return
     */
    private String getFileName(HttpURLConnection conn) {
        String filename = this.downloadUrl.substring(this.downloadUrl.lastIndexOf('/') + 1);
       
        if(filename==null || "".equals(filename.trim())){//如果获取不到文件名称
            for (int i = 0;; i++) {
                String mine = conn.getHeaderField(i);
               
                if (mine == null) break;
               
                if("content-disposition".equals(conn.getHeaderFieldKey(i).toLowerCase())){
                    Matcher m = Pattern.compile(".*filename=(.*)").matcher(mine.toLowerCase());
                    if(m.find()) return m.group(1);
                }
            }
           
            filename = UUID.randomUUID()+ ".tmp";//默认取一个文件名
        }
       
        return filename;
    }
   
    /**
     *  开始下载文件
     * @param listener 监听下载数量的变化,如果不需要了解实时下载的数量,可以设置为null
     * @return 已下载文件大小
     * @throws Exception
     */
    public int download(DownloadProgressListener listener) throws Exception{
        try {
            RandomAccessFile randOut = new RandomAccessFile(this.saveFile, "rw");
            if(this.fileSize>0) randOut.setLength(this.fileSize);
            randOut.close();
            URL url = new URL(this.downloadUrl);
           
            if(this.data.size() != this.threads.length){
                this.data.clear();
               
                for (int i = 0; i < this.threads.length; i++) {
                    this.data.put(i+1, 0);//初始化每条线程已经下载的数据长度为0
                }
            }
           
            for (int i = 0; i < this.threads.length; i++) {//开启线程进行下载
                int downLength = this.data.get(i+1);
               
                if(downLength < this.block && this.downloadSize<this.fileSize){//判断线程是否已经完成下载,否则继续下载   
                    this.threads[i] = new DownloadThread(this, url, this.saveFile, this.block, this.data.get(i+1), i+1);
                    this.threads[i].setPriority(7);
                    this.threads[i].start();
                }else{
                    this.threads[i] = null;
                }
            }
           
            this.fileService.save(this.downloadUrl, this.data);
            boolean notFinish = true;//下载未完成
           
            while (notFinish) {// 循环判断所有线程是否完成下载
                Thread.sleep(900);
                notFinish = false;//假定全部线程下载完成
               
                for (int i = 0; i < this.threads.length; i++){
                    if (this.threads[i] != null && !this.threads[i].isFinish()) {//如果发现线程未完成下载
                        notFinish = true;//设置标志为下载没有完成
                       
                        if(this.threads[i].getDownLength() == -1){//如果下载失败,再重新下载
                            this.threads[i] = new DownloadThread(this, url, this.saveFile, this.block, this.data.get(i+1), i+1);
                            this.threads[i].setPriority(7);
                            this.threads[i].start();
                        }
                    }
                }   
               
                if(listener!=null) listener.onDownloadSize(this.downloadSize);//通知目前已经下载完成的数据长度
            }
           
            fileService.delete(this.downloadUrl);
        } catch (Exception e) {
            print(e.toString());
            throw new Exception("file download fail");
        }
        return this.downloadSize;
    }
   
    /**
     * 获取Http响应头字段
     * @param http
     * @return
     */
    public static Map<String, String> getHttpResponseHeader(HttpURLConnection http) {
        Map<String, String> header = new LinkedHashMap<String, String>();
       
        for (int i = 0;; i++) {
            String mine = http.getHeaderField(i);
            if (mine == null) break;
            header.put(http.getHeaderFieldKey(i), mine);
        }
       
        return header;
    }
   
    /**
     * 打印Http头字段
     * @param http
     */
    public static void printResponseHeader(HttpURLConnection http){
        Map<String, String> header = getHttpResponseHeader(http);
       
        for(Map.Entry<String, String> entry : header.entrySet()){
            String key = entry.getKey()!=null ? entry.getKey()+ ":" : "";
            print(key+ entry.getValue());
        }
    }

    private static void print(String msg){
        Log.i(TAG, msg);
    }
}

package com.android.network;
import java.io.File;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;

import android.util.Log;

public class DownloadThread extends Thread {
    private static final String TAG = "DownloadThread";
    private File saveFile;
    private URL downUrl;
    private int block;
   
    /* 下载开始位置  */
    private int threadId = -1;   
    private int downLength;
    private boolean finish = false;
    private FileDownloader downloader;
   
    public DownloadThread(FileDownloader downloader, URL downUrl, File saveFile, int block, int downLength, int threadId) {
        this.downUrl = downUrl;
        this.saveFile = saveFile;
        this.block = block;
        this.downloader = downloader;
        this.threadId = threadId;
        this.downLength = downLength;
    }
   
    @Override
    public void run() {
        if(downLength < block){//未下载完成
            try {
                HttpURLConnection http = (HttpURLConnection) downUrl.openConnection();
                http.setConnectTimeout(5 * 1000);
                http.setRequestMethod("GET");
                http.setRequestProperty("Accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*");
                http.setRequestProperty("Accept-Language", "zh-CN");
                http.setRequestProperty("Referer", downUrl.toString());
                http.setRequestProperty("Charset", "UTF-8");
                int startPos = block * (threadId - 1) + downLength;//开始位置
                int endPos = block * threadId -1;//结束位置
                http.setRequestProperty("Range", "bytes=" + startPos + "-"+ endPos);//设置获取实体数据的范围
                http.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)");
                http.setRequestProperty("Connection", "Keep-Alive");
               
                InputStream inStream = http.getInputStream();
                byte[] buffer = new byte[1024];
                int offset = 0;
                print("Thread " + this.threadId + " start download from position "+ startPos);
                RandomAccessFile threadfile = new RandomAccessFile(this.saveFile, "rwd");
                threadfile.seek(startPos);
               
                while ((offset = inStream.read(buffer, 0, 1024)) != -1) {
                    threadfile.write(buffer, 0, offset);
                    downLength += offset;
                    downloader.update(this.threadId, downLength);
                    downloader.append(offset);
                }
               
                threadfile.close();
                inStream.close();
                print("Thread " + this.threadId + " download finish");
                this.finish = true;
            } catch (Exception e) {
                this.downLength = -1;
                print("Thread "+ this.threadId+ ":"+ e);
            }
        }
    }
   
    private static void print(String msg){
        Log.i(TAG, msg);
    }
   
    /**
     * 下载是否完成
     * @return
     */
    public boolean isFinish() {
        return finish;
    }
   
    /**
     * 已经下载的内容大小
     * @return 如果返回值为-1,代表下载失败
     */
    public long getDownLength() {
        return downLength;
    }
}

   AlarmManager am = (AlarmManager) context
                .getSystemService(Context.ALARM_SERVICE);

        Intent intent = new Intent(
                "com.android.settings.action.REQUEST_POWER_OFF");

        PendingIntent pendingIntent = PendingIntent.getBroadcast(context, 0,
                intent, PendingIntent.FLAG_CANCEL_CURRENT);
        am = (AlarmManager) context
                .getSystemService(Context.ALARM_SERVICE);
        am.set(AlarmManager.RTC_WAKEUP, time, pendingIntent);

        Intent newIntent = new Intent(Intent.ACTION_REQUEST_SHUTDOWN);
        newIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        startActivity(newIntent);

#define ANDROID_ALARM_GET_TIME(type)        ALARM_IOW(4, type, struct timespec)
#define ANDROID_ALARM_SET_RTC               _IOW('a', 5, struct timespec)

/* we define ANDROID_RTC_ALARM_SET for auto power off */
#define ANDROID_RTC_ALARM_SET               _IOW('a', 7, int)

#define ANDROID_ALARM_BASE_CMD(cmd)         (cmd & ~(_IOC(0, 0, 0xf0, 0)))

b) bionic/libc/kernel/common/linux/android_alarm.h

#define ANDROID_RTC_ALARM_SET _IOW('a', 7, int)

#include <mach/pmic.h>

static void android_server_AlarmManagerService_updateRtcAlarm(JNIEnv* env, jobject obj, jint fd, jint seconds)
{
#if HAVE_ANDROID_OS
    int result = ioctl(fd, ANDROID_RTC_ALARM_SET, &seconds);
    LOGE("set rtc alarm to %d later: %sn", seconds, strerror(errno));
    if (result < 0)
    {
        LOGE("Unable to set rtc alarm to %d later: %sn", seconds, strerror(errno));
    }
#endif
}

{"updateRtcAlarm", "(II)V", (void*)android_server_AlarmManagerService_updateRtcAlarm},

    public void setRepeating(int type, long triggerAtTime, long interval,
            PendingIntent operation) {
        if (operation == null) {
            Slog.w(TAG, "set/setRepeating ignored because there is no intent");
            return;
        }
        synchronized (mLock) {
            Alarm alarm = new Alarm();
            alarm.type = type;
            alarm.when = triggerAtTime;
            alarm.repeatInterval = interval;
            alarm.operation = operation;

            // Remove this alarm if already scheduled.
            removeLocked(operation);

            if (localLOGV) Slog.v(TAG, "set: " + alarm);

            int index = addAlarmLocked(alarm);
            if (index == 0) {
                setLocked(alarm);
            }

            // Start to setup auto power on alarm
            if ((alarm.type == AlarmManager.ELAPSED_REALTIME_WAKEUP) &&
                                alarm.operation.getTargetPackage().equals("com.android.settings")) {
                updateRtcAlarm(mDescriptor, (int)((alarm.when - System.currentTimeMillis()) / 1000));
            }
            // End to setup auto power on alarm
        }
    }

      AlarmManager am = (AlarmManager) context
                .getSystemService(Context.ALARM_SERVICE);
        Intent intent = new Intent(
                "com.android.settings.action.REQUEST_POWER_ON");
        PendingIntent pendingIntent = PendingIntent.getBroadcast(context, 0,
                intent, PendingIntent.FLAG_CANCEL_CURRENT);
        am = (AlarmManager) context
                .getSystemService(Context.ALARM_SERVICE);
        am.set(AlarmManager.ELAPSED_REALTIME_WAKEUP, time, pendingIntent);

package com.android.drag;import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Bundle;
import android.util.DisplayMetrics;
import android.view.MotionEvent;
import android.view.View;

/**
 * Android通过手势实现图像拖拽功能
 * @author Administrator
 *
 */
public class DragActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // setContentView(R.layout.main);
        View view = new ImageDragView(this);
       
        setContentView(view);
    }

    class ImageDragView extends View {

        private float x1;
        private float y1;
        private float x2;
        private float y2;

        public ImageDragView(Context context) {
            super(context);
            // TODO Auto-generated constructor stub
        }

        @Override
        public boolean onTouchEvent(MotionEvent event) {
            // TODO Auto-generated method stub

            float size = event.getSize();

            int szi = (int) size;
            int dxi = szi >> 12;
            int dyit = ((1 << 12) - 1);
            int dyi = szi & dyit;

            DisplayMetrics metrics = getResources().getDisplayMetrics();
           
            float dx = metrics.widthPixels * dxi / (float) dyit;
            float dy = metrics.heightPixels * dyi / (float) dyit;

            x1 = event.getX();
            y1 = event.getY();

            x2 = x1 + dx;
            y2 = y1 + dy;

            invalidate();

            return true;
        }

        @Override
        protected void onDraw(Canvas canvas) {
            // TODO Auto-generated method stub
            super.onDraw(canvas);

            float r = (float) Math.sqrt((x1 - x2) * (x1 - x2) + (y1 - y2)
                    * (y1 - y2)) / 2;
            r = 100 >= r ? 100 : r;

            Paint paint = new Paint();
            paint.setColor(Color.RED);
            canvas.drawCircle(x1, y1, r, paint);
        }
    }