使用Android自带的DownloadManager实现下载功能
DownloadManager.Request request = new DownloadManager.Request(Uri.parse(APK_URL));request.setDestinationInExternalPublicDir(DOWNLOAD_FOLDER_NAME, DOWNLOAD_FILE_NAME);request.setTitle(getString(R.string.download_notification_title));request.setDescription("meilishuo desc");request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);request.setVisibleInDownloadsUi(false);// request.allowScanningByMediaScanner();// request.setAllowedNetworkTypes(DownloadManager.Request.NETWORK_WIFI);// request.setShowRunningNotification(false);// request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_HIDDEN);request.setMimeType("application/cn.trinea.download.file");downloadId = downloadManager.enqueue(request);downloadManager.enqueue是加入下载请求到下载管理类中，并且会返回一个下载的ID。
request.setAllowedNetworkTypes(DownloadManager.Request.NETWORK_WIFI);大文件只能在wifi下下载
需要注册一个下载完成的广播，自定义这个广播
class CompleteReceiver extends BroadcastReceiver {@Overridepublic void onReceive(Context context, Intent intent) {/*** get the id of download which have download success, if the id is my id and it's status is successful,* then install it**/long completeDownloadId = intent.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID, -1);if (completeDownloadId == downloadId) {initData();updateView();// if download successful, install apkif (downloadManagerPro.getStatusById(downloadId) == DownloadManager.STATUS_SUCCESSFUL) {String apkFilePath = new StringBuilder(Environment.getExternalStorageDirectory().getAbsolutePath()).append(File.separator).append(DOWNLOAD_FOLDER_NAME).append(File.separator).append(DOWNLOAD_FILE_NAME).toString();install(context, apkFilePath);}}}};这里的intent.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID, -1);的DownloadManager.EXTRA_DOWNLOAD_ID是DownloadManager类里的参数，使用下面方法注册广播
/** register download success broadcast **/registerReceiver(completeReceiver, new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE));用到的IntentFilter是下载完成的Filter
然后会通知这个广播，并且返回的intent里面包含了DownloadManager.EXTRA_DOWNLOAD_ID的参数。
关于DownloadManager的其他用法可以查看api文档
这里再介绍下DownloadManager.Query的用法。
显而易见Query是内部类。有query.setFilterById和query.setFilterByStatus两个方法，
query.setFilterById就是把downloadManager.enqueue返回的id放进去作为查询的条件；
query.setFilterByStatus(DownloadManager.STATUS_FAILED|DownloadManager.STATUS_PENDING|DownloadManager.STATUS_RUNNING|DownloadManager.STATUS_SUCCESSFUL);可以进行拼接查询的条件。
Cursor cur = downloadManager.query(query);
这里用的Query查询Downloads的数据库，但是只可以查询本应用下载的数据，
/** * 使用DownloadManager.Query查询Downloads的DB，但是在stackoverflow中的解释是 * You can’t access this DB from my application. For your own downloads, * use DownloadManager.Query to check on your download status. Data about downloads is not shared to other apps. */
所以要是想通过DownloadManager.Query查询系统所有的下载记录是不可行的。
但是需求有要怎么办呢？
记得ApiDemo里有用户联系人使用Uri的方式查询联系人contacts，进入Root Explore观察com.android.providers.downloads包里的DB数据库内容时，，发现下载的记录里有content://media/external/file/452122
这种内容，所以可以这样获取到下载的文件
Cursor cursor = getContentResolver().query(Uri.parse("content://media/external/file"), null, null, null, null);测试下返回的字段
/*String[] downNames = cursor.getColumnNames();String str = "";for(int i=0;i<downNames.length;i++){str += downNames[i]+",";}*/if(cursor!=null&&cursor.moveToLast()){//cursor.moveToPrevious()String displayname = cursor.getString(cursor.getColumnIndex("_display_name"));String name = cursor.getString(cursor.getColumnIndex("name"));String title = cursor.getString(cursor.getColumnIndex("title"));String description = cursor.getString(cursor.getColumnIndex("description"));String data = cursor.getString(cursor.getColumnIndex("_data"));String bucket = cursor.getString(cursor.getColumnIndex("bucket_display_name"));downloadTip.setText(displayname+","+name+","+title+","+description+","+data+","+bucket);}根据自己需求提取字段。
有时不但是必要的，而且是很有必要的。
