使用Android系统提供的DownloadManager来下载文件

在android2.3以后android系统提供了一个系统组件来供其他app调用来下载东西，使用起来非常方便。

例如我们可以拿来下载app的新版本apk，同时在同时注册一个广播接收器来接收下载完成时DownloadManager发出的的广播，然后自动安装程序。

SDK在API Level 9中加入了DownloadManager服务，可以将长时间的下载任务交给系统，完全由系统管理。

直接看实例代码：

package com.hebaijun.downloadtest; 

import java.io.UnsupportedEncodingException;
import java.net.URLEncoder; 

import android.app.Activity;
import android.app.DownloadManager;
import android.app.DownloadManager.Request;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.SharedPreferences;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.util.Log;
import android.webkit.MimeTypeMap; 

public class DownloadTestActivity extends Activity {
  private DownloadManager downloadManager;
  private SharedPreferences prefs;
  private static final String DL_ID = "downloadId";
  /** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    downloadManager = (DownloadManager)getSystemService(DOWNLOAD_SERVICE);
    prefs = PreferenceManager.getDefaultSharedPreferences(this);
  }
  @Override
  protected void onPause() {
    // TODO Auto-generated method stub
    super.onPause();
    unregisterReceiver(receiver);
  }
  @Override
  protected void onResume() {
    // TODO Auto-generated method stub
    super.onResume();
    if(!prefs.contains(DL_ID)) {
      String url = "http://10.0.2.2/android/film/G3.mp4";
      //开始下载
      Uri resource = Uri.parse(encodeGB(url));
      DownloadManager.Request request = new DownloadManager.Request(resource);
      request.setAllowedNetworkTypes(Request.NETWORK_MOBILE | Request.NETWORK_WIFI);
      request.setAllowedOverRoaming(false);
      //设置文件类型
      MimeTypeMap mimeTypeMap = MimeTypeMap.getSingleton();
      String mimeString = mimeTypeMap.getMimeTypeFromExtension(MimeTypeMap.getFileExtensionFromUrl(url));
      request.setMimeType(mimeString);
      //在通知栏中显示
      request.setShowRunningNotification(true);
      request.setVisibleInDownloadsUi(true);
      //sdcard的目录下的download文件夹
      request.setDestinationInExternalPublicDir("/download/", "G3.mp4");
      request.setTitle("移动G3广告");
      long id = downloadManager.enqueue(request);
      //保存id
      prefs.edit().putLong(DL_ID, id).commit();
    } else {
      //下载已经开始，检查状态
      queryDownloadStatus();
    }  

    registerReceiver(receiver, new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE));
  } 

  /**
   * 如果服务器不支持中文路径的情况下需要转换url的编码。
   * @param string
   * @return
   */
  public String encodeGB(String string)
  {
    //转换中文编码
    String split[] = string.split("/");
    for (int i = 1; i < split.length; i++) {
      try {
        split[i] = URLEncoder.encode(split[i], "GB2312");
      } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
      }
      split[0] = split[0]+"/"+split[i];
    }
    split[0] = split[0].replaceAll("\\+", "%20");//处理空格
    return split[0];
  } 

  private BroadcastReceiver receiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
      //这里可以取得下载的id，这样就可以知道哪个文件下载完成了。适用与多个下载任务的监听
      Log.v("intent", ""+intent.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID, 0));
      queryDownloadStatus();
    }
  };  

  private void queryDownloadStatus() {
    DownloadManager.Query query = new DownloadManager.Query();
    query.setFilterById(prefs.getLong(DL_ID, 0));
    Cursor c = downloadManager.query(query);
    if(c.moveToFirst()) {
      int status = c.getInt(c.getColumnIndex(DownloadManager.COLUMN_STATUS));
      switch(status) {
      case DownloadManager.STATUS_PAUSED:
        Log.v("down", "STATUS_PAUSED");
      case DownloadManager.STATUS_PENDING:
        Log.v("down", "STATUS_PENDING");
      case DownloadManager.STATUS_RUNNING:
        //正在下载，不做任何事情
        Log.v("down", "STATUS_RUNNING");
        break;
      case DownloadManager.STATUS_SUCCESSFUL:
        //完成
        Log.v("down", "下载完成");
        break;
      case DownloadManager.STATUS_FAILED:
        //清除已下载的内容，重新下载
        Log.v("down", "STATUS_FAILED");
        downloadManager.remove(prefs.getLong(DL_ID, 0));
        prefs.edit().clear().commit();
        break;
      }
    }
  }
}

最后需要的权限是：

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

如果需要隐藏下载工具的提示和显示，修改代码：

request.setShowRunningNotification(false);
request.setVisibleInDownloadsUi(false);

加入下面的权限：

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

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持我们。