Android实现文件下载进度显示功能

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"  xmlns:tools="http://schemas.android.com/tools"  android:layout_width="match_parent"  android:layout_height="match_parent"  tools:context="${relativePackage}.${activityClass}" >   <ProgressBar    android:id="@+id/progressBar"    style="?android:attr/progressBarStyleHorizontal"    android:layout_width="match_parent"    android:layout_height="wrap_content"    android:max="100" />   <TextView    android:id="@+id/textView"    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:layout_below="@+id/progressBar"    android:layout_centerHorizontal="true"    android:layout_marginTop="24dp"    android:text="TextView" />   <ImageView    android:id="@+id/imageView"    android:layout_marginTop="24dp"    android:layout_width="match_parent"    android:layout_height="wrap_content"    android:layout_alignParentBottom="true"    android:layout_below="@+id/textView"    android:contentDescription="@string/app_name"    android:src="@drawable/ic_launcher" /> </RelativeLayout>

public class MainActivity extends Activity {   ProgressBar pb;   TextView tv;  ImageView imageView;  int fileSize;    int downLoadFileSize;    String fileEx,fileNa,filename;   //用来接收线程发送来的文件下载量，进行UI界面的更新  private Handler handler = new Handler(){      @Override      public void handleMessage(Message msg)      {//定义一个Handler，用于处理下载线程与UI间通讯     if (!Thread.currentThread().isInterrupted())     {        switch (msg.what)      {         case 0:          pb.setMax(fileSize);       case 1:          pb.setProgress(downLoadFileSize);          int result = downLoadFileSize * 100 / fileSize;          tv.setText(result + "%");          break;         case 2:          Toast.makeText(MainActivity.this, "文件下载完成", Toast.LENGTH_SHORT).show();         FileInputStream fis = null;        try {          fis = new FileInputStream(Environment.getExternalStorageDirectory() + File.separator + "/ceshi/" + filename);        } catch (FileNotFoundException e) {          e.printStackTrace();        }        Bitmap bitmap = BitmapFactory.decodeStream(fis); ///把流转化为Bitmap图        imageView.setImageBitmap(bitmap);        break;            case -1:          String error = msg.getData().getString("error");        Toast.makeText(MainActivity.this, error, Toast.LENGTH_SHORT).show();          break;        }       }       super.handleMessage(msg);      }     };     @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    pb=(ProgressBar)findViewById(R.id.progressBar);    tv=(TextView)findViewById(R.id.textView);    imageView = (ImageView) findViewById(R.id.imageView);    tv.setText("0%");    new Thread(){      public void run(){        try {          //下载文件，参数：第一个URL，第二个存放路径          down_file("http://cdnq.duitang.com/uploads/item/201406/15/20140615203435_ABQMa.jpeg", Environment.getExternalStorageDirectory() + File.separator + "/ceshi/");        } catch (ClientProtocolException e) {          // TODO Auto-generated catch block          e.printStackTrace();        } catch (IOException e) {          // TODO Auto-generated catch block          e.printStackTrace();        }       }      }.start();       }       /**   * 文件下载   * @param url：文件的下载地址   * @param path：文件保存到本地的地址   * @throws IOException   */  public void down_file(String url,String path) throws IOException{      //下载函数         filename=url.substring(url.lastIndexOf("/") + 1);    //获取文件名      URL myURL = new URL(url);    URLConnection conn = myURL.openConnection();      conn.connect();      InputStream is = conn.getInputStream();      this.fileSize = conn.getContentLength();//根据响应获取文件大小      if (this.fileSize <= 0) throw new RuntimeException("无法获知文件大小 ");      if (is == null) throw new RuntimeException("stream is null");    File file1 = new File(path);    File file2 = new File(path+filename);    if(!file1.exists()){      file1.mkdirs();    }    if(!file2.exists()){      file2.createNewFile();    }    FileOutputStream fos = new FileOutputStream(path+filename);      //把数据存入路径+文件名      byte buf[] = new byte[1024];    downLoadFileSize = 0;      sendMsg(0);      do{        //循环读取        int numread = is.read(buf);        if (numread == -1)        {         break;        }        fos.write(buf, 0, numread);        downLoadFileSize += numread;           sendMsg(1);//更新进度条      } while (true);          sendMsg(2);//通知下载完成           try{        is.close();      } catch (Exception ex) {        Log.e("tag", "error: " + ex.getMessage(), ex);      }       }       //在线程中向Handler发送文件的下载量，进行UI界面的更新  private void sendMsg(int flag)    {      Message msg = new Message();      msg.what = flag;      handler.sendMessage(msg);    }       }

<uses-permission android:name="android.permission.INTERNET"/>