Android实现简单断点续传和下载到本地功能

compile 'com.loopj.android:android-async-http:1.4.9'

public class MainActivity extends AppCompatActivity {
 protected static final String TAG = "OtherActivity";

 //下载线程的数量
 private final static int threadsize = 3;

 protected static final int SET_MAX = 0;
 public static final int UPDATE_VIEW = 1;


 private ProgressBar pb;
 private Button bt_download;

 private Button bt_pause;
 private TextView tv_info;
 //显示进度和更新进度
 private Handler mHandler = new Handler() {
  public void handleMessage(android.os.Message msg) {
   switch (msg.what) {
    case SET_MAX://设置进度条的最大值
     int filelength = msg.arg1;
     pb.setMax(filelength);
     break;
    case UPDATE_VIEW://更新进度条 和 下载的比率
     int len = msg.arg1;//新下载的长度
     pb.setProgress(pb.getProgress() + len);//设置进度条的刻度

     int max = pb.getMax();//获取进度的最大值
     int progress = pb.getProgress();//获取已经下载的数据量
     // 下载：30 总：100
     int result = (progress * 100) / max;

     tv_info.setText("下载:" + result + "%");

     break;

    default:
     break;
   }
  }

  ;
 };

 String uri = "http://c.hiphotos.baidu.com/image/pic/item/b90e7bec54e736d1e51217c292504fc2d46269f3.jpg";

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  //找到控件
  pb = (ProgressBar) findViewById(R.id.pb);
  tv_info = (TextView) findViewById(R.id.tv_info);

  bt_download = (Button) findViewById(R.id.bt_download);
  bt_pause = (Button) findViewById(R.id.bt_pause);

  //数据的回显
  //确定下载的文件
  String name = getFileName(uri);
  File file = new File(Environment.getExternalStorageDirectory(), name);
  if (file.exists()) {//文件存在回显
   //获取文件的大小
   int filelength = (int) file.length();
   pb.setMax(filelength);
   try {
    //统计原来所有的下载量
    int count = 0;
    //读取下载记录文件
    for (int threadid = 0; threadid