Android系统下载管理DownloadManager功能介绍及使用示例

可运行代码地址可见DownloadManager Demo，效果图如下：




关于下载管理的废话

XHTML

Android网络应用开发中经常需要下载文件，如音乐、应用、系统升级包。一般的要求是统一的管理(暂停、继续、取消)中心、断点续传、并发下载、wifi及3g的不同处理、下载完成后处理、管理中心与应用的交互。可以使用RandomAccessFile和多线程自己实现。三方应用通常要么跳转到浏览器下载，要么勉强实现后却像天天动听、海豚浏览器那样bug百出(鄙视下)。实际上Android下载管理已经提供了功能强大(超乎你的想象)的API供第三方调用，google play、chrome都会调用系统下载管理进行下载。本文就以一个示例着手介绍DownloadManager的使用及丰富功能。

1	Android网络应用开发中经常需要下载文件，如音乐、应用、系统升级包。一般的要求是统一的管理(暂停、继续、取消)中心、断点续传、并发下载、wifi及3g的不同处理、下载完成后处理、管理中心与应用的交互。可以使用RandomAccessFile和多线程自己实现。三方应用通常要么跳转到浏览器下载，要么勉强实现后却像天天动听、海豚浏览器那样bug百出(鄙视下)。实际上Android下载管理已经提供了功能强大(超乎你的想象)的API供第三方调用，googleplay、chrome都会调用系统下载管理进行下载。本文就以一个示例着手介绍DownloadManager的使用及丰富功能。

一、DownloadManager简单介绍

DownloadManager是系统开放给第三方应用使用的类，包含两个静态内部类DownloadManager.Query和DownloadManager.Request。DownloadManager.Request用来请求一个下载，DownloadManager.Query用来查询下载信息，这两个类的具体功能会在后面穿插介绍。DownloadManager的源码可见DownloadManager@Grepcode。

DownloadManager主要提供了下面几个接口：

public long enqueue(Request request)执行下载，返回downloadId，downloadId可用于后面查询下载信息。若网络不满足条件、Sdcard挂载中、超过最大并发数等异常会等待下载，正常则直接下载。

public int remove(long… ids)删除下载，若下载中取消下载。会同时删除下载文件和记录。

public Cursor query(Query query)查询下载信息。

public static Long getRecommendedMaxBytesOverMobile(Context context通过移动网络下载的最大字节数

public String getMimeTypeForDownloadedFile(long id)得到下载的mimeType，如何设置后面会进行介绍

其它：通过查看代码我们可以发现还有个CursorTranslator私有静态内部类。这个类主要对Query做了一层代理。将DownloadProvider和DownloadManager之间做个映射。将DownloadProvider中的十几种状态对应到了DownloadManager中的五种状态，DownloadProvider中的失败、暂停原因转换为了DownloadManager的原因。

二、下载管理示例

下面具体介绍利用DownloadManager进行下载。

1、AndroidManifest中添加权限

Java

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

1 2	<uses-permissionandroid:name="android.permission.INTERNET"/> <uses-permissionandroid:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

网络访问权限是必须的，下载地址为sdcard的话需要添加sdcard写权限。

2、调用DownloadManager.Request开始下载

Java

DownloadManager downloadManager = (DownloadManager)getSystemService(DOWNLOAD_SERVICE);
String apkUrl = "http://img.meilishuo.net/css/images/AndroidShare/Meilishuo_3.6.1_10006.apk";
DownloadManager.Request request = new DownloadManager.Request(Uri.parse(apkUrl));
request.setDestinationInExternalPublicDir("Trinea", "MeiLiShuo.apk");
// request.setTitle("MeiLiShuo");
// request.setDescription("MeiLiShuo desc");
// request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
// request.setAllowedNetworkTypes(DownloadManager.Request.NETWORK_WIFI);
// request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_HIDDEN);
// request.setMimeType("application/cn.trinea.download.file");
long downloadId = downloadManager.enqueue(request);

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DownloadManagerdownloadManager = (DownloadManager)getSystemService(DOWNLOAD_SERVICE); String apkUrl= "http://img.meilishuo.net/css/images/AndroidShare/Meilishuo_3.6.1_10006.apk"; DownloadManager.Requestrequest =new DownloadManager.Request(Uri.parse(apkUrl)); request.setDestinationInExternalPublicDir("Trinea","MeiLiShuo.apk"); // request.setTitle("MeiLiShuo"); // request.setDescription("MeiLiShuo desc"); // request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED); // request.setAllowedNetworkTypes(DownloadManager.Request.NETWORK_WIFI); // request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_HIDDEN); // request.setMimeType("application/cn.trinea.download.file"); longdownloadId =downloadManager.enqueue(request);

上面调用downloadManager的enqueue接口进行下载，返回唯一的downloadId。

DownloadManager.Request除了构造函数的Uri必须外，其他设置都为可选设置。下面逐个介绍下：

request.setDestinationInExternalPublicDir(“Trinea”, “MeiLiShuo.apk”);表示设置下载地址为sd卡的Trinea文件夹，文件名为MeiLiShuo.apk。

setDestinationInExternalPublicDir源码

Java

public Request setDestinationInExternalPublicDir(String dirType, String subPath) {
File file = Environment.getExternalStoragePublicDirectory(dirType);

Xlog.v(XLOGTAG, "setExternalPublicDir: dirType " +
dirType + " subPath " + subPath +
"file" + file);

if (file.exists()) {
if (!file.isDirectory()) {
throw new IllegalStateException(file.getAbsolutePath() +
" already exists and is not a directory");
}
} else {
if (!file.mkdir()) {
throw new IllegalStateException("Unable to create directory: "+
file.getAbsolutePath());
}
}
setDestinationFromBase(file, subPath);
return this;
}

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publicRequest setDestinationInExternalPublicDir(StringdirType,String subPath){ File file= Environment.getExternalStoragePublicDirectory(dirType); Xlog.v(XLOGTAG,"setExternalPublicDir: dirType "+ dirType+ " subPath "+ subPath+ "file"+ file); if(file.exists()){ if(!file.isDirectory()){ thrownew IllegalStateException(file.getAbsolutePath()+ " already exists and is not a directory"); } }else { if(!file.mkdir()){ thrownew IllegalStateException("Unable to create directory: "+ file.getAbsolutePath()); } } setDestinationFromBase(file,subPath); returnthis; }

从源码中我们可以看出下载完整目录为Environment.getExternalStoragePublicDirectory(dirType)。不过file是通过file.mkdir()创建的，这样如果上级目录不存在就会新建文件夹异常。所以下载前我们最好自己调用File的mkdirs方法递归创建子目录，如下：

Java

File folder = new File(folderName);
return (folder.exists() && folder.isDirectory()) ? true : folder.mkdirs();

1 2	Filefolder =new File(folderName); return (folder.exists()&& folder.isDirectory())? true: folder.mkdirs();

否则，会报异常

java.lang.IllegalStateException: Unable to create directory: /storage/sdcard0/Trinea/aa
at android.app.DownloadManager$Request.setDestinationInExternalPublicDir(DownloadManager.java)

1 2	java.lang.IllegalStateException:Unable to createdirectory: /storage/sdcard0/Trinea/aa at android.app.DownloadManager$Request.setDestinationInExternalPublicDir(DownloadManager.java)

其他设置下载路径接口为setDestinationUri，setDestinationInExternalFilesDir，setDestinationToSystemCache。其中setDestinationToSystemCache仅限系统app使用。

request.allowScanningByMediaScanner();表示允许MediaScanner扫描到这个文件，默认不允许。
request.setTitle(“MeiLiShuo”);设置下载中通知栏提示的标题

request.setDescription(“MeiLiShuo desc”);设置下载中通知栏提示的介绍

request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);

表示下载进行中和下载完成的通知栏是否显示。默认只显示下载中通知。VISIBILITY_VISIBLE_NOTIFY_COMPLETED表示下载完成后显示通知栏提示。VISIBILITY_HIDDEN表示不显示任何通知栏提示，这个需要在AndroidMainfest中添加权限android.permission.DOWNLOAD_WITHOUT_NOTIFICATION.

request.setAllowedNetworkTypes(DownloadManager.Request.NETWORK_WIFI);

表示下载允许的网络类型，默认在任何网络下都允许下载。有NETWORK_MOBILE、NETWORK_WIFI、NETWORK_BLUETOOTH三种及其组合可供选择。如果只允许wifi下载，而当前网络为3g，则下载会等待。

request.setAllowedOverRoaming(boolean allow)移动网络情况下是否允许漫游。

request.setMimeType(“application/cn.trinea.download.file”);

设置下载文件的mineType。因为下载管理Ui中点击某个已下载完成文件及下载完成点击通知栏提示都会根据mimeType去打开文件，所以我们可以利用这个属性。比如上面设置了mimeType为application/cn.trinea.download.file，我们可以同时设置某个Activity的intent-filter为application/cn.trinea.download.file，用于响应点击的打开文件。

Java

<intent-filter>
<action android:name="android.intent.action.VIEW" />

<category android:name="android.intent.category.DEFAULT" />

<data android:mimeType="application/cn.trinea.download.file" />
</intent-filter>

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<intent-filter> <actionandroid:name="android.intent.action.VIEW"/> <categoryandroid:name="android.intent.category.DEFAULT"/> <dataandroid:mimeType="application/cn.trinea.download.file"/> </intent-filter>

request.addRequestHeader(String header, String value)

添加请求下载的网络链接的http头，比如User-Agent，gzip压缩等

3 下载进度状态监听及查询

下载进度状态监听代码

Java

class DownloadChangeObserver extends ContentObserver {

public DownloadChangeObserver(){
super(handler);
}

@Override
public void onChange(boolean selfChange) {
updateView();
}

}

public void updateView() {
int[] bytesAndStatus = downloadManagerPro.getBytesAndStatus(downloadId);
handler.sendMessage(handler.obtainMessage(0, bytesAndStatus[0], bytesAndStatus[1],
bytesAndStatus[2]));
}

private DownloadChangeObserver downloadObserver;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.download_manager_demo);
……
downloadObserver = new DownloadChangeObserver();
}

@Override
protected void onResume() {
super.onResume();
/** observer download change **/
getContentResolver().registerContentObserver(DownloadManagerPro.CONTENT_URI, true,
downloadObserver);
}

@Override
protected void onPause() {
super.onPause();
getContentResolver().unregisterContentObserver(downloadObserver);
}

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

classDownloadChangeObserverextends ContentObserver{ publicDownloadChangeObserver(){ super(handler); } @Override publicvoid onChange(booleanselfChange){ updateView(); } } public voidupdateView(){ int[]bytesAndStatus = downloadManagerPro.getBytesAndStatus(downloadId); handler.sendMessage(handler.obtainMessage(0,bytesAndStatus[0],bytesAndStatus[1], bytesAndStatus[2])); } private DownloadChangeObserverdownloadObserver; @Override protectedvoid onCreate(BundlesavedInstanceState){ super.onCreate(savedInstanceState); setContentView(R.layout.download_manager_demo); …… downloadObserver= newDownloadChangeObserver(); } @Override protectedvoid onResume(){ super.onResume(); /** observer download change **/ getContentResolver().registerContentObserver(DownloadManagerPro.CONTENT_URI,true, downloadObserver); } @Override protectedvoid onPause(){ super.onPause(); getContentResolver().unregisterContentObserver(downloadObserver); }

其中我们会监听Uri.parse(“content://downloads/my_downloads”)。然后查询下载状态和进度，发送handler进行更新，handler中处理就是设置进度条和状态等。
其中DownloadManagerPro.getBytesAndStatus的主要代码如下，可直接引入TrineaAndroidCommon@Github(欢迎star和fork^_^)作为你项目的library(如何拉取代码及添加公共库)：

下载进度状态查询代码

Java

public int[] getBytesAndStatus(long downloadId) {
int[] bytesAndStatus = new int[] { -1, -1, 0 };
DownloadManager.Query query = new DownloadManager.Query().setFilterById(downloadId);
Cursor c = null;
try {
c = downloadManager.query(query);
if (c != null && c.moveToFirst()) {
bytesAndStatus[0] = c.getInt(c.getColumnIndexOrThrow(DownloadManager.COLUMN_BYTES_DOWNLOADED_SO_FAR));
bytesAndStatus[1] = c.getInt(c.getColumnIndexOrThrow(DownloadManager.COLUMN_TOTAL_SIZE_BYTES));
bytesAndStatus[2] = c.getInt(c.getColumnIndex(DownloadManager.COLUMN_STATUS));
}
} finally {
if (c != null) {
c.close();
}
}
return bytesAndStatus;
}

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publicint[]getBytesAndStatus(longdownloadId){ int[]bytesAndStatus = newint[]{ -1,-1,0 }; DownloadManager.Queryquery =new DownloadManager.Query().setFilterById(downloadId); Cursorc =null; try{ c= downloadManager.query(query); if(c!= null&& c.moveToFirst()){ bytesAndStatus[0]= c.getInt(c.getColumnIndexOrThrow(DownloadManager.COLUMN_BYTES_DOWNLOADED_SO_FAR)); bytesAndStatus[1]= c.getInt(c.getColumnIndexOrThrow(DownloadManager.COLUMN_TOTAL_SIZE_BYTES)); bytesAndStatus[2]= c.getInt(c.getColumnIndex(DownloadManager.COLUMN_STATUS)); } }finally { if(c!= null){ c.close(); } } returnbytesAndStatus; }

从上面代码可以看出我们主要调用DownloadManager.Query()进行查询。DownloadManager.Query为下载管理对外开放的信息查询类，主要包括以下接口：
setFilterById(long… ids)根据下载id进行过滤

setFilterByStatus(int flags)根据下载状态进行过滤

setOnlyIncludeVisibleInDownloadsUi(boolean value)根据是否在download ui中可见进行过滤。

orderBy(String column, int direction)根据列进行排序，不过目前仅支持DownloadManager.COLUMN_LAST_MODIFIED_TIMESTAMP和DownloadManager.COLUMN_TOTAL_SIZE_BYTES排序。

4 下载成功监听

下载完成后，下载管理会发出DownloadManager.ACTION_DOWNLOAD_COMPLETE这个广播，并传递downloadId作为参数。通过接受广播我们可以打开对下载完成的内容进行操作。代码如下：

下载成功监听

Java

class CompleteReceiver extends BroadcastReceiver {

@Override
public void onReceive(Context context, Intent intent) {
// get complete download id
long completeDownloadId = intent.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID, -1);
// to do here
}
};

private CompleteReceiver completeReceiver;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.download_manager_demo);

…
completeReceiver = new CompleteReceiver();
/** register download success broadcast **/
registerReceiver(completeReceiver,
new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE));
}

@Override
protected void onDestroy() {
super.onDestroy();
unregisterReceiver(completeReceiver);
}

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classCompleteReceiver extends BroadcastReceiver{ @Override publicvoid onReceive(Contextcontext,Intent intent){ // get complete download id longcompleteDownloadId = intent.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID,-1); // to do here } }; privateCompleteReceiver completeReceiver; @Override protectedvoid onCreate(BundlesavedInstanceState){ super.onCreate(savedInstanceState); setContentView(R.layout.download_manager_demo); … completeReceiver= newCompleteReceiver(); /** register download success broadcast **/ registerReceiver(completeReceiver, newIntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE)); } @Override protectedvoid onDestroy(){ super.onDestroy(); unregisterReceiver(completeReceiver); }

5、响应通知栏点击

(1) 响应下载中通知栏点击

点击下载中通知栏提示，系统会对下载的应用单独发送Action为DownloadManager.ACTION_NOTIFICATION_CLICKED广播。intent.getData为content://downloads/all_downloads/29669，最后一位为downloadId。

如果同时下载多个应用，intent会包含DownloadManager.EXTRA_NOTIFICATION_CLICK_DOWNLOAD_IDS这个key，表示下载的的downloadId数组。这里设计到下载管理通知栏的显示机制，会在下一篇具体介绍。

(2) 响应下载完成通知栏点击

下载完后会调用下面代码进行处理，从中我们可以发现系统会调用View action根据mimeType去查询。所以可以利用我们在介绍的DownloadManager.Request的setMimeType函数。

openDownload源码

Java

private void openDownload(Context context, Cursor cursor) {
String filename = cursor.getString(cursor.getColumnIndexOrThrow(Downloads.Impl._DATA));
String mimetype = cursor.getString(cursor.getColumnIndexOrThrow(Downloads.Impl.COLUMN_MIME_TYPE));
Uri path = Uri.parse(filename);
// If there is no scheme, then it must be a file
if (path.getScheme() == null) {
path = Uri.fromFile(new File(filename));
}
Intent activityIntent = new Intent(Intent.ACTION_VIEW);
mimetype = DownloadDrmHelper.getOriginalMimeType(context, filename, mimetype);
activityIntent.setDataAndType(path, mimetype);
activityIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
try {
context.startActivity(activityIntent);
} catch (ActivityNotFoundException ex) {
Log.d(Constants.TAG, "no activity for " + mimetype, ex);
}
}

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privatevoid openDownload(Contextcontext,Cursor cursor){ Stringfilename =cursor.getString(cursor.getColumnIndexOrThrow(Downloads.Impl._DATA)); Stringmimetype =cursor.getString(cursor.getColumnIndexOrThrow(Downloads.Impl.COLUMN_MIME_TYPE)); Uri path= Uri.parse(filename); // If there is no scheme, then it must be a file if(path.getScheme()== null){ path= Uri.fromFile(newFile(filename)); } IntentactivityIntent = newIntent(Intent.ACTION_VIEW); mimetype= DownloadDrmHelper.getOriginalMimeType(context,filename,mimetype); activityIntent.setDataAndType(path,mimetype); activityIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK); try{ context.startActivity(activityIntent); }catch (ActivityNotFoundExceptionex){ Log.d(Constants.TAG,"no activity for " + mimetype,ex); } }

如果界面上过多元素需要更新，且网速较快不断的执行onChange会对页面性能有一定影响。推荐ScheduledExecutorService定期查询，如下:

Java

public static ScheduledExecutorService scheduledExecutorService = Executors.newScheduledThreadPool(3);
Runnable command = new Runnable() {

@Override
public void run() {
updateView();
}
};
scheduledExecutorService.scheduleAtFixedRate(command, 0, 3, TimeUnit.SECONDS);

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publicstatic ScheduledExecutorServicescheduledExecutorService= Executors.newScheduledThreadPool(3); Runnable command= newRunnable(){ @Override publicvoid run(){ updateView(); } }; scheduledExecutorService.scheduleAtFixedRate(command,0,3,TimeUnit.SECONDS);

表示3秒定时刷新