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                Android網路程式設計 --斷點續傳下載檔案
2014年2月28日 2月最後一天
前言：關於斷點續傳下載檔案，這個我好幾個月之前面試的時候就遇到過，那時我確實迷惑了一下，Android開發分兩種，一種是介面開發，一種是研發應用型，面試官問過我屬於哪一種，我記得那次面試對我打擊很大，因為它證明了我對Android還不夠熟悉，水平還不到家，反正感覺被面試官鄙視了。不過到現在我已經不那麼想了，不管是介面開發還是研發應用，靠的都是動手能力

，能做出東西人才是有用之人，面試主要看你對技術有沒有概念，實際開發中誰管你會不會那個技術，反正你給我把效果做出來就行了，做不出東西就給我滾蛋，所以經驗對應屆生來說是一大詬病，所以建議在大學的雛鳥們多動手做點東西出來，而不是死磕大學那些無用的課程。
廢話多了一點，下面我就來介紹本篇部落格的技術要點： HTTP協議，我想上過計算機網路課程的童鞋肯定不陌生，但是誰又能說自己能把它實際運用上了，只有在實際專案開發的時候才會用到。Http算是Android網路中最常用到的網路協議了，客戶端通過http通訊與伺服器進行資料互動，GET方法和POST方法想必是再熟悉不過了，本篇部落格介紹一個比較實用的技術，斷點續傳下載

，光看這個名字就感覺挺高大上，確實是，想實現它需要對http協議有一定的瞭解，並且對多執行緒機制比較熟悉，還有就是Android中非同步更新UI的原理不能讓程式出現卡頓的現象。 在說http斷點續傳之前需要重點了解http協議頭部的Range欄位 Range 

　　 用於請求頭中，指定第一個位元組的位置和最後一個位元組的位置，一般格式：

　　 Range:(unit=first byte pos)-[last byte pos] 

比如你要請求下載一個MP3檔案，url為：http://abv.cn/music/光輝歲月.mp3

你需要通過http傳送get請求，請求頭欄位可能如下

GET /music/%E5%85%89%E8%BE%89%E5%B2%81%E6%9C%88.mp3 HTTP/1.1
Host: abv.cn
Connection: keep-alive
Accept-Encoding: identity;q=1, *;q=0
User-Agent: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.16 50.63 Safari/537.36
Accept: */*
Referer: http://abv.cn/music/%E5%85%89%E8%BE%89%E5%B2%81%E6%9C%88.mp3
Accept-Language: zh-CN,zh;q=0.8,en;q=0.6
Range: bytes=0-// 請求內容位元組範圍 如果直接請求的話，自然位元組從0開始了。 響應頭部欄位： HTTP/1.1 206 Partial Content
Date: Tue, 25 Feb 2014 06:05:26 GMT
Server: Apache/2.4.3 (Unix) OpenSSL/1.0.1c PHP/5.4.7
Last-Modified: Sun, 23 Feb 2014 12:53:00 GMT
ETag: "49aa24-4f31255b92300"
Accept-Ranges: bytes
Content-Length: 4827684// 這個表示檔案大小
Content-Range: bytes 0-4827683/4827684// 檔案位元組範圍
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Content-Type: audio/mpeg

關於其他欄位的含義，我在這裡就不解釋了，自己動手查去，哪個不懂就查哪個。上面很直觀的展示了請求很響應的內容。
那麼斷點續傳的原理就是通過http請求你想下載內容的位元組範圍，假如之前已經下載了一部分，但你有事需要暫停下載，那麼下次下載的時候你接著後面繼續下載就可以了。 但再實際開發中，可能需要下載比較大的檔案，並且不能下載太久，這時候我們需要利用多執行緒來分段下載我們需要的內容。下面是在Android平臺下實現的多執行緒斷點續傳下載： http://download.csdn.net/detail/wwj_748/6975041,原始碼已經給你們準備好了。
程式碼中註釋已經很清楚，小巫在這裡就多說了。 /MultiThreadDownload/src/com/wwj/download/db/DBOpenHelper.java 資料庫幫助類，用於建立儲存下載進度的表

package com.wwj.download.db;import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteOpenHelper;public class DBOpenHelper extends SQLiteOpenHelper { private static final String DBNAME = "eric.db"; private static final int VERSION = 1; public DBOpenHelper(Context context) {  super(context, DBNAME, null, VERSION); } @Override public void onCreate(SQLiteDatabase db) {  // 建立filedownlog表  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); }}

/MultiThreadDownload/src/com/wwj/net/download/FileDownloader.java
檔案下載器

package com.wwj.net.download;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 android.content.Context;import android.util.Log;/** * 檔案下載器 *  */public class FileDownloader { private static final String TAG = "FileDownloader"; private Context context; private FileService fileService; /* 停止下載 */ private boolean exit; /* 已下載檔案長度 */ private int downloadSize = 0; /* 原始檔案長度 */ private int fileSize = 0; /* 執行緒數 */ private DownloadThread[] threads; /* 本地儲存檔案 */ private File saveFile; /* 快取各執行緒下載的長度 */ private Map<Integer, Integer> data = new ConcurrentHashMap<Integer, Integer>(); /* 每條執行緒下載的長度 */ private int block; /* 下載路徑 */ private String downloadUrl; /**  * 獲取執行緒數  */ public int getThreadSize() {  return threads.length; } /**  * 退出下載  */ public void exit() {  this.exit = true; } public boolean getExit() {  return this.exit; } /**  * 獲取檔案大小  *   * @return  */ public int getFileSize() {  return fileSize; } /**  * 累計已下載大小  *   * @param size  */ protected synchronized void append(int size) {  downloadSize += size; } /**  * 更新指定執行緒最後下載的位置  *   * @param threadId  *            執行緒id  * @param pos  *            最後下載的位置  */ protected synchronized void update(int threadId, int pos) {  this.data.put(threadId, pos);  this.fileService.update(this.downloadUrl, threadId, pos); } /**  * 構建檔案下載器  *   * @param downloadUrl  *            下載路徑  * @param fileSaveDir  *            檔案儲存目錄  * @param threadNum  *            下載執行緒數  */ 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()) // 判斷目錄是否存在，如果不存在，建立目錄    fileSaveDir.mkdirs();   this.threads = new DownloadThread[threadNum];// 例項化執行緒陣列   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(); // 連線   printResponseHeader(conn);   if (conn.getResponseCode() == 200) { // 響應成功    this.fileSize = conn.getContentLength();// 根據響應獲取檔案大小    if (this.fileSize <= 0)     throw new RuntimeException("Unkown file size ");    String filename = getFileName(conn);// 獲取檔名稱    this.saveFile = new File(fileSaveDir, filename);// 構建儲存檔案    Map<Integer, Integer> logdata = fileService      .getData(downloadUrl);// 獲取下載記錄    if (logdata.size() > 0) {// 如果存在下載記錄     for (Map.Entry<Integer, Integer> entry : logdata.entrySet())      data.put(entry.getKey(), entry.getValue());// 把各條執行緒已經下載的資料長度放入data中    }    if (this.data.size() == this.threads.length) {// 下面計算所有執行緒已經下載的資料總長度     for (int i = 0; i < this.threads.length; i++) {      this.downloadSize += this.data.get(i + 1);     }     print("已經下載的長度" + this.downloadSize);    }    // 計算每條執行緒下載的資料長度    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");  } } /**  * 獲取檔名  */ private String getFileName(HttpURLConnection conn) {  String filename = this.downloadUrl.substring(this.downloadUrl    .lastIndexOf('/') + 1);  if (filename == null || "".equals(filename.trim())) {// 如果獲取不到檔名稱   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";// 預設取一個檔名  }  return filename; } /**  * 開始下載檔案  *   * @param listener  *            監聽下載數量的變化,如果不需要了解實時下載的數量,可以設定為null  * @return 已下載檔案大小  * @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); // 預分配fileSize大小   randOut.close();   URL url = new URL(this.downloadUrl);   if (this.data.size() != this.threads.length) {// 如果原先未曾下載或者原先的下載執行緒數與現在的執行緒數不一致    this.data.clear();    for (int i = 0; i < this.threads.length; i++) {     this.data.put(i + 1, 0);// 初始化每條執行緒已經下載的資料長度為0    }    this.downloadSize = 0;   }   for (int i = 0; i < this.threads.length; i++) {// 開啟執行緒進行下載    int downLength = this.data.get(i + 1);    if (downLength < this.block      && this.downloadSize < this.fileSize) {// 判斷執行緒是否已經完成下載,否則繼續下載     this.threads[i] = new DownloadThread(this, url,       this.saveFile, this.block, this.data.get(i + 1),       i + 1);     this.threads[i].setPriority(7); // 設定執行緒優先順序     this.threads[i].start();    } else {     this.threads[i] = null;    }   }   fileService.delete(this.downloadUrl);// 如果存在下載記錄，刪除它們，然後重新新增   fileService.save(this.downloadUrl, this.data);   boolean notFinish = true;// 下載未完成   while (notFinish) {// 迴圈判斷所有執行緒是否完成下載    Thread.sleep(900);    notFinish = false;// 假定全部執行緒下載完成    for (int i = 0; i < this.threads.length; i++) {     if (this.threads[i] != null && !this.threads[i].isFinish()) {// 如果發現執行緒未完成下載      notFinish = true;// 設定標誌為下載沒有完成      if (this.threads[i].getDownLength() == -1) {// 如果下載失敗,再重新下載       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);// 通知目前已經下載完成的資料長度   }   if (downloadSize == this.fileSize)    fileService.delete(this.downloadUrl);// 下載完成刪除記錄  } catch (Exception e) {   print(e.toString());   throw new Exception("file download error");  }  return this.downloadSize; } /**  * 獲取Http響應頭欄位  *   * @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; } /**  * 列印Http頭欄位  *   * @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); }}

/MultiThreadDownload/src/com/wwj/net/download/FileService.java

package com.wwj.net.download;import java.util.HashMap;import java.util.Map;import android.content.Context;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import com.wwj.download.db.DBOpenHelper;/** * 業務bean *  */public class FileService { private DBOpenHelper openHelper; public FileService(Context context) {  openHelper = new DBOpenHelper(context); } /**  * 獲取每條執行緒已經下載的檔案長度  *   * @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; } /**  * 儲存每條執行緒已經下載的檔案長度  *   * @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(); } /**  * 實時更新每條執行緒已經下載的檔案長度  *   * @param path  * @param map  */ public void update(String path, int threadId, int pos) {  SQLiteDatabase db = openHelper.getWritableDatabase();  db.execSQL(    "update filedownlog set downlength=? where downpath=? and threadid=?",    new Object[] { pos, path, threadId });  db.close(); } /**  * 當檔案下載完成後，刪除對應的下載記錄  *   * @param path  */ public void delete(String path) {  SQLiteDatabase db = openHelper.getWritableDatabase();  db.execSQL("delete from filedownlog where downpath=?",    new Object[] { path });  db.close(); }}

/MultiThreadDownload/src/com/wwj/net/download/DownloadThread.java
下載執行緒類

package com.wwj.net.download;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; /* 下載開始位置 */ 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) {// 未下載完成   try {    HttpURLConnection http = (HttpURLConnection) downUrl      .openConnection();    http.setConnectTimeout(5 * 1000); // 設定連線超時    http.setRequestMethod("GET"); // 設定請求方法，這裡是“GET”    // 瀏覽器可接受的MIME型別    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"); // 瀏覽器所希望的語言種類，當伺服器能夠提供一種以上的語言版本時要用到    http.setRequestProperty("Referer", downUrl.toString());// 包含一個URL，使用者從該URL代表的頁面出發訪問當前請求的頁面。    http.setRequestProperty("Charset", "UTF-8"); // 字符集    int startPos = block * (threadId - 1) + downLength;// 開始位置    int endPos = block * threadId - 1;// 結束位置    http.setRequestProperty("Range", "bytes=" + startPos + "-"      + endPos);// 設定獲取實體資料的範圍    // 瀏覽器型別，如果Servlet返回的內容與瀏覽器型別有關則該值非常有用。    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"); // 設定為持久連線    // 得到輸入流    InputStream inStream = http.getInputStream();    byte[] buffer = new byte[1024];    int offset = 0;    print("Thread " + this.threadId      + " start download from position " + startPos);    // 隨機訪問檔案    RandomAccessFile threadfile = new RandomAccessFile(      this.saveFile, "rwd");    // 定位到pos位置    threadfile.seek(startPos);    while (!downloader.getExit()      && (offset = inStream.read(buffer, 0, 1024)) != -1) {     // 寫入檔案     threadfile.write(buffer, 0, offset);     downLength += offset; // 累加下載的大小     downloader.update(this.threadId, downLength); // 更新指定執行緒下載最後的位置     downloader.append(offset); // 累加已下載大小    }    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); } /**  * 下載是否完成  *   * @return  */ public boolean isFinish() {  return finish; } /**  * 已經下載的內容大小  *   * @return 如果返回值為-1,代表下載失敗  */ public long getDownLength() {  return downLength; }}

/MultiThreadDownload/src/com/wwj/net/download/DownloadProgressListener.java
下載進度介面

package com.wwj.net.download;public interface DownloadProgressListener { public void onDownloadSize(int size);}

/MultiThreadDownload/src/com/wwj/download/MainActivity.java
介面

package com.wwj.download;import java.io.File;import java.io.UnsupportedEncodingException;import java.net.URLEncoder;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;import com.wwj.net.download.DownloadProgressListener;import com.wwj.net.download.FileDownloader;public class MainActivity extends Activity { private static final int PROCESSING = 1; private static final int FAILURE = -1; private EditText pathText; // url地址 private TextView resultView; private Button downloadButton; private Button stopButton; private ProgressBar progressBar; private Handler handler = new UIHandler(); private final class UIHandler extends Handler {  public void handleMessage(Message msg) {   switch (msg.what) {   case PROCESSING: // 更新進度    progressBar.setProgress(msg.getData().getInt("size"));    float num = (float) progressBar.getProgress()      / (float) progressBar.getMax();    int result = (int) (num * 100); // 計算進度    resultView.setText(result + "%");    if (progressBar.getProgress() == progressBar.getMax()) { // 下載完成     Toast.makeText(getApplicationContext(), R.string.success,       Toast.LENGTH_LONG).show();    }    break;   case FAILURE: // 下載失敗    Toast.makeText(getApplicationContext(), R.string.error,      Toast.LENGTH_LONG).show();    break;   }  } } @Override protected void onCreate(Bundle savedInstanceState) {  super.onCreate(savedInstanceState);  setContentView(R.layout.main);  pathText = (EditText) findViewById(R.id.path);  resultView = (TextView) findViewById(R.id.resultView);  downloadButton = (Button) findViewById(R.id.downloadbutton);  stopButton = (Button) findViewById(R.id.stopbutton);  progressBar = (ProgressBar) findViewById(R.id.progressBar);  ButtonClickListener listener = new ButtonClickListener();  downloadButton.setOnClickListener(listener);  stopButton.setOnClickListener(listener); } private final class ButtonClickListener implements View.OnClickListener {  @Override  public void onClick(View v) {   switch (v.getId()) {   case R.id.downloadbutton: // 開始下載    // http://abv.cn/music/光輝歲月.mp3，可以換成其他檔案下載的連結    String path = pathText.getText().toString();    String filename = path.substring(path.lastIndexOf('/') + 1);    try {     // URL編碼（這裡是為了將中文進行URL編碼）     filename = URLEncoder.encode(filename, "UTF-8");    } catch (UnsupportedEncodingException e) {     e.printStackTrace();    }    path = path.substring(0, path.lastIndexOf("/") + 1) + filename;    if (Environment.getExternalStorageState().equals(      Environment.MEDIA_MOUNTED)) {     // File savDir =     // Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MOVIES);     // 儲存路徑     File savDir = Environment.getExternalStorageDirectory();     download(path, savDir);    } else {     Toast.makeText(getApplicationContext(),       R.string.sdcarderror, Toast.LENGTH_LONG).show();    }    downloadButton.setEnabled(false);    stopButton.setEnabled(true);    break;   case R.id.stopbutton: // 暫停下載    exit();    Toast.makeText(getApplicationContext(),      "Now thread is Stopping!!", Toast.LENGTH_LONG).show();    downloadButton.setEnabled(true);    stopButton.setEnabled(false);    break;   }  }  /*   * 由於使用者的輸入事件(點選button, 觸控式螢幕幕....)是由主執行緒負責處理的，如果主執行緒處於工作狀態，   * 此時使用者產生的輸入事件如果沒能在5秒內得到處理，系統就會報“應用無響應”錯誤。   * 所以在主執行緒裡不能執行一件比較耗時的工作，否則會因主執行緒阻塞而無法處理使用者的輸入事件，   * 導致“應用無響應”錯誤的出現。耗時的工作應該在子執行緒裡執行。   */  private DownloadTask task;  private void exit() {   if (task != null)    task.exit();  }  private void download(String path, File savDir) {   task = new DownloadTask(path, savDir);   new Thread(task).start();  }  /**   *    * UI控制元件畫面的重繪(更新)是由主執行緒負責處理的，如果在子執行緒中更新UI控制元件的值，更新後的值不會重繪到螢幕上   * 一定要在主執行緒裡更新UI控制元件的值，這樣才能在螢幕上顯示出來，不能在子執行緒中更新UI控制元件的值   *    */  private final class DownloadTask implements Runnable {   private String path;   private File saveDir;   private FileDownloader loader;   public DownloadTask(String path, File saveDir) {    this.path = path;    this.saveDir = saveDir;   }   /**    * 退出下載    */   public void exit() {    if (loader != null)     loader.exit();   }   DownloadProgressListener downloadProgressListener = new DownloadProgressListener() {    @Override    public void onDownloadSize(int size) {     Message msg = new Message();     msg.what = PROCESSING;     msg.getData().putInt("size", size);     handler.sendMessage(msg);    }   };   public void run() {    try {     // 例項化一個檔案下載器     loader = new FileDownloader(getApplicationContext(), path,       saveDir, 3);     // 設定進度條最大值     progressBar.setMax(loader.getFileSize());     loader.download(downloadProgressListener);    } catch (Exception e) {     e.printStackTrace();     handler.sendMessage(handler.obtainMessage(FAILURE)); // 傳送一條空訊息物件    }   }  } }}

以上就是所有核心程式碼了，許可權和佈局檔案我就不貼了，自己可以下我提供的demo來看。




           

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