//創(chuàng)建下載任務(wù),downloadUrl就是下載鏈接
DownloadManager.Request request = new DownloadManager.Request(Uri.parse(downloadUrl));
//指定下載路徑和下載文件名
request.setDestinationInExternalPublicDir("/download/", fileName);
//獲取下載管理器
DownloadManager downloadManager= (DownloadManager) mContext.getSystemService(Context.DOWNLOAD_SERVICE);
//將下載任務(wù)加入下載隊列，否則不會進行下載
downloadManager.enqueue(request); 

 //使用系統(tǒng)下載器下載
private void downloadAPK(String versionUrl, String versionName) {
    //創(chuàng)建下載任務(wù)
    DownloadManager.Request request = new DownloadManager.Request(Uri.parse(versionUrl));
    request.setAllowedOverRoaming(false);//漫游網(wǎng)絡(luò)是否可以下載

    //設(shè)置文件類型，可以在下載結(jié)束后自動打開該文件
    MimeTypeMap mimeTypeMap = MimeTypeMap.getSingleton();
    String mimeString = mimeTypeMap.getMimeTypeFromExtension(MimeTypeMap.getFileExtensionFromUrl(versionUrl));
    request.setMimeType(mimeString);

    //在通知欄中顯示，默認就是顯示的
    request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE);
    request.setVisibleInDownloadsUi(true);

    //sdcard的目錄下的download文件夾，必須設(shè)置
    request.setDestinationInExternalPublicDir("/download/", versionName);
    //request.setDestinationInExternalFilesDir(),也可以自己制定下載路徑

    //將下載請求加入下載隊列
    downloadManager = (DownloadManager) mContext.getSystemService(Context.DOWNLOAD_SERVICE);
    //加入下載隊列后會給該任務(wù)返回一個long型的id，
    //通過該id可以取消任務(wù)，重啟任務(wù)等等，看上面源碼中框起來的方法
    mTaskId = downloadManager.enqueue(request);

    //注冊廣播接收者，監(jiān)聽下載狀態(tài)
    mContext.registerReceiver(receiver,
        new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE));
  } 

   //廣播接受者，接收下載狀態(tài)
  private BroadcastReceiver receiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
      checkDownloadStatus();//檢查下載狀態(tài)
    }
  }; 

 //檢查下載狀態(tài)
  private void checkDownloadStatus() {
    DownloadManager.Query query = new DownloadManager.Query();
    query.setFilterById(mTaskId);//篩選下載任務(wù)，傳入任務(wù)ID，可變參數(shù)
    Cursor c = downloadManager.query(query);
    if (c.moveToFirst()) {
      int status = c.getInt(c.getColumnIndex(DownloadManager.COLUMN_STATUS));
      switch (status) {
        case DownloadManager.STATUS_PAUSED:
          MLog.i(">>>下載暫停");
        case DownloadManager.STATUS_PENDING:
          MLog.i(">>>下載延遲");
        case DownloadManager.STATUS_RUNNING:
          MLog.i(">>>正在下載");
          break;
        case DownloadManager.STATUS_SUCCESSFUL
          MLog.i(">>>下載完成");
          //下載完成安裝APK
          //downloadPath = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getAbsolutePath() + File.separator + versionName;
          installAPK(new File(downloadPath));
          break;
        case DownloadManager.STATUS_FAILED:
          MLog.i(">>>下載失敗");
          break;
      }
    }
  } 

   //下載到本地后執(zhí)行安裝
  protected void installAPK(File file) {
    if (!file.exists()) return;
    Intent intent = new Intent(Intent.ACTION_VIEW);
    Uri uri = Uri.parse("file://" + file.toString());
    intent.setDataAndType(uri, "application/vnd.android.package-archive");
    //在服務(wù)中開啟activity必須設(shè)置flag,后面解釋
    intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
    mContext.startActivity(intent);
  }