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小牛知识库。