第8章? 深入理解ContentService 和 AccountManagerService

提示這兩個(gè)Service的難度都不大，它們?cè)谠O(shè)計(jì)結(jié)構(gòu)上有較大的相似性，在內(nèi)容上也有一定的關(guān)聯(lián)。另外，作為本書(shū)最后一章，筆者照例會(huì)留一些難度適中的問(wèn)題或知識(shí)點(diǎn)供讀者自行分析研究。

提示在設(shè)計(jì)模式中，通知機(jī)制對(duì)應(yīng)的模式是Observer模式，即觀察者模式。

public void run() {

?? ......

??ContentService.main(context,

???????????????????factoryTest == SystemServer.FACTORY_TEST_LOW_LEVEL);

?? ......

}

public static IContentService main(Contextcontext, boolean factoryTest) {

? ?//構(gòu)造ContentService實(shí)例

??ContentService service = new ContentService(context, factoryTest);

?? //將ContentService注冊(cè)到ServiceManager中，其注冊(cè)名叫“content”

??ServiceManager.addService(ContentResolver.CONTENT_SERVICE_NAME,

??????????????????????????????? ?service);

?? returnservice;

}

ContentService(Context context, booleanfactoryTest) {

?? ?mContext = context;

???mFactoryTest = factoryTest;

?? ?getSyncManager(); //獲取同步服務(wù)管理對(duì)象，接下來(lái)看它的代碼

}

private SyncManager getSyncManager() {

???synchronized(mSyncManagerLock) {

???? try {

??????????//創(chuàng)建一個(gè)SyncManager實(shí)例，它是ContentService中負(fù)責(zé)數(shù)據(jù)同步服務(wù)的

??????????//主力成員。留待8.4節(jié)再詳細(xì)分析它

???????????if (mSyncManager == null) mSyncManager = new

??????????????????????????????????????? SyncManager(mContext,mFactoryTest);

?????? }......

???????????return mSyncManager;

???? }

}

public final void registerContentObserver(Uri uri,

??????????? booleannotifyForDescendents,ContentObserver observer){

? /*

? ?注意registerContentObserver傳遞的參數(shù)，其中：

?? uri是客戶端設(shè)置的它所需要監(jiān)聽(tīng)的數(shù)據(jù)項(xiàng)的地址，用Uri來(lái)表示

?? notifyForDescendents：如果該值為true，則所有地址包含此uri的數(shù)據(jù)項(xiàng)發(fā)生變化時(shí)

?? 都會(huì)觸發(fā)通知。否則只有完全符合該uri地址的數(shù)據(jù)項(xiàng)發(fā)生變化時(shí)才會(huì)觸發(fā)通知。以文件夾和

?? 其中的文件為例，若uri指向某文件夾，則需設(shè)置notifyForDescendents為true。即該文件

?? 夾下的任何文件發(fā)生變化，都需要通知監(jiān)聽(tīng)者。

?? observer是客戶端設(shè)置的監(jiān)聽(tīng)對(duì)象。當(dāng)數(shù)據(jù)項(xiàng)發(fā)生變化時(shí)，該對(duì)象的onChange函數(shù)將被調(diào)用

? */

? try {???

???????????/*

????????????調(diào)用ContentService的registerContentObserver函數(shù)，其第三個(gè)參數(shù)是

??????????? ?observer.getContentObserver的返回值，它是什么呢？

???????????*/

???????????getContentService().registerContentObserver(uri,

?????????????????????????????????? notifyForDescendents,

????? ?????????????????????????????observer.getContentObserver());

??????? } ......

?}

注意IContentObserver.java由aidl處理IContentObserver.aidl生成，其位置在out/targer/common/obj/JAVA_LIBRARIES/framework_intermediates/src/core/java/android/database/IContentObserver.java中。

public void registerContentObserver(Uri uri,boolean notifyForDescendents,

????? ?????????IContentObserver observer) {

?? ??......

???synchronized (mRootNode) {

????//ContentService要做的事情其實(shí)很簡(jiǎn)單，就是保存uri和observer的對(duì)應(yīng)關(guān)系到

???? //其內(nèi)部變量mRootNode中

????mRootNode.addObserverLocked(uri, observer, notifyForDescendents,

????????????????????mRootNode, Binder.getCallingUid(),

???????????????????Binder.getCallingPid());

?}

public int update(Uri uri, ContentValuesinitialValues, String userWhere,

????????? ???????????String[] whereArgs) {

?? int count;

?? int match= URI_MATCHER.match(uri);

??DatabaseHelper database = getDatabaseForUri(uri);

?? //找到對(duì)應(yīng)的數(shù)據(jù)庫(kù)對(duì)象

??SQLiteDatabase db = database.getWritableDatabase();

?? ......

? ?synchronized (sGetTableAndWhereParam) {

????getTableAndWhere(uri, match, userWhere, sGetTableAndWhereParam);

???? switch(match) {

????? ???......

???? ???case VIDEO_MEDIA:

???? ???case VIDEO_MEDIA_ID:{

??? ??????ContentValues values = newContentValues(initialValues);

??? ??????values.remove(ImageColumns.BUCKET_ID);

????? ????values.remove(ImageColumns.BUCKET_DISPLAY_NAME);

?????? ???......//調(diào)用SQLiteDatabase的update函數(shù)更新數(shù)據(jù)庫(kù)

?????? ???count =db.update(sGetTableAndWhereParam.table, values,

???????????????????????????????sGetTableAndWhereParam.where, whereArgs);

?????? ??.......

?? ??????}......//其他處理

???? }......//synchronized處理結(jié)束

?? ?if (count > 0 &&!db.inTransaction()) //調(diào)用notifyChange觸發(fā)通知

??????? getContext().getContentResolver().notifyChange(uri,null);

?? returncount;

}

public void notifyChange(Uri uri, ContentObserverobserver) {

???? //在一般情況下，observer參數(shù)為null。調(diào)用另一個(gè)notifyChange函數(shù)，直接來(lái)看它

????notifyChange(uri, observer, true);

?}

public void notifyChange(Uri uri, ContentObserverobserver,

????????????????????????? ?????boolean syncToNetwork) {

? //第三個(gè)參數(shù)syncToNetwork用于控制是否需要發(fā)起一次數(shù)據(jù)同步請(qǐng)求

? try {

?????? //調(diào)用ContentService的notifyChange函數(shù)

????? ?getContentService().notifyChange(

?????????????uri, observer == null ? null : observer.getContentObserver(),

?????????????observer != null && observer.deliverSelfNotifications(),

?????????????syncToNetwork);

??????? } ......

}

public void notifyChange(Uri uri, IContentObserverobserver,

?????boolean observerWantsSelfNotifications, boolean syncToNetwork) {

? longidentityToken = clearCallingIdentity();

? try {

?????????ArrayList<ObserverCall> calls = newArrayList<ObserverCall>();

????????? //從根節(jié)點(diǎn)開(kāi)始搜索需要通知的觀察者，結(jié)果保存在calls數(shù)組中

?????????synchronized (mRootNode) {

???????????????mRootNode.collectObserversLocked(uri, 0, observer,

?????????????????????????????? observerWantsSelfNotifications,calls);

????????? }

????????final int numCalls = calls.size();

???????? for(int i=0; i<numCalls; i++) {

??????????????ObserverCall oc = calls.get(i);

??????????????try {

???????????????????/*

???????????????????? 調(diào)用客戶端IContentObserver Bn端，即ContentObserver

??? ?????????????????內(nèi)部類(lèi)Transport的onChange函數(shù)。最后再由Transport調(diào)用

???????????????????? 客戶端提供的ContentObserver子類(lèi)的onChange函數(shù)

??????????????????*/

???????????????????oc.mObserver.onChange(oc.mSelfNotify);

???????????????} ......//異常處理

???????????}

???????????if (syncToNetwork) {

???????????????SyncManager syncManager = getSyncManager();

???????????????if (syncManager != null) {

???????????????????//發(fā)起一次同步請(qǐng)求，相關(guān)內(nèi)容留待8.4節(jié)再分析

???????????????????syncManager.scheduleLocalSync(null,

????????????????????????????????????????? ?uri.getAuthority());

???????????????}

???????????}

??????? }finally {

???????????restoreCallingIdentity(identityToken);

??????? }

??? }

private static class Proxy implementsandroid.database.IContentObserver {

???? privateandroid.os.IBinder mRemote;

???? ......

???? publicvoid onChange(boolean selfUpdate)

????????? ????????????throws android.os.RemoteException {

??????? android.os.Parcel_data = android.os.Parcel.obtain();

??????? try{

?????????? _data.writeInterfaceToken(DESCRIPTOR);

?????????? _data.writeInt(((selfUpdate)? (1) : (0)));

??????????//調(diào)用客戶端1的ContentObserver Bn端的onChange函數(shù)

?????????? mRemote.transact(Stub.TRANSACTION_onChange,_data, null,

??????????????????????????? ????????????android.os.IBinder.FLAG_ONEWAY);

????? ??} finally {

??????????? _data.recycle();

???? ???}

???? }

???? ......

}

public booleanonPreferenceTreeClick(PreferenceScreen preferenceScreen,

??????????????????????????? ?Preference preference) {

?

?? ......

?? if(preference == mMtp) {

????????mUsbManager.setCurrentFunction(UsbManager.USB_FUNCTION_MTP,true);

???????updateToggles(UsbManager.USB_FUNCTION_MTP);

?? } else if(preference == mPtp) {

????????mUsbManager.setCurrentFunction(UsbManager.USB_FUNCTION_PTP, true);

??????? ?updateToggles(UsbManager.USB_FUNCTION_PTP);

?? }

?? returntrue;

?}

public void onClick(DialogInterface dialog, intwhich) {

??if (which == DialogInterface.BUTTON_POSITIVE){

???????mOkClicked = true;

?????? //設(shè)置Settings數(shù)據(jù)庫(kù)ADB對(duì)應(yīng)的數(shù)據(jù)項(xiàng)值為1

???????Settings.Secure.putInt(getActivity().getContentResolver(),

???????????????????Settings.Secure.ADB_ENABLED, 1);

?? } else

???????mEnableAdb.setChecked(false);//界面更新

?}

private class AdbSettingsObserver extendsContentObserver {

?? ......

?? publicvoid onChange(boolean selfChange) {

?????? ?//從數(shù)據(jù)庫(kù)中取出對(duì)應(yīng)項(xiàng)的值

?????? ?boolean enable =(Settings.Secure.getInt(mContentResolver,

????????????????????????????Settings.Secure.ADB_ENABLED, 0) > 0);

??????????//發(fā)送MSG_ENABLE_ADB消息，UsbDeviceManager將處理此消息

????????? ?mHandler.sendMessage(MSG_ENABLE_ADB, enable);

???? }

}

? ......

??//注冊(cè)AccountManagerService到ServiceManager，服務(wù)名為“account”

??ServiceManager.addService(Context.ACCOUNT_SERVICE,

????????????????????????????????????newAccountManagerService(context));

public AccountManagerService(Context context) {

?? //調(diào)用另外一個(gè)構(gòu)造函數(shù)，其第三個(gè)參數(shù)將構(gòu)造一個(gè)AccountAuthenticatorCache對(duì)象，它是

?? //什么呢？見(jiàn)下文分析

???this(context,context.getPackageManager(),

????????????new? AccountAuthenticatorCache(context));

}

public AccountAuthenticatorCache(Context context){

? /*

? ACTION_AUTHENTICATOR_INTENT值為"android.accounts.AccountAuthenticator"

? AUTHENTICATOR_META_DATA_NAME值為"android.accounts.AccountAuthenticator"

? AUTHENTICATOR_ATTRIBUTES_NAME值為"account-authenticator"

? */

??super(context,

?????????? AccountManager.ACTION_AUTHENTICATOR_INTENT,

??????????AccountManager.AUTHENTICATOR_META_DATA_NAME,

??????????AccountManager.AUTHENTICATOR_ATTRIBUTES_NAME, sSerializer);

?}

public RegisteredServicesCache(Context context,String interfaceName,

???????????????????????????????????? StringmetaDataName, String attributeName,

????????????????????????????XmlSerializerAndParser<V>serializerAndParser) {

??? mContext= context;

?? ?//保存?zhèn)鬟f進(jìn)來(lái)的參數(shù)

???mInterfaceName = interfaceName;

???mMetaDataName = metaDataName;

???mAttributesName = attributeName;

???mSerializerAndParser = serializerAndParser;

?

??? FiledataDir = Environment.getDataDirectory();

??? FilesystemDir = new File(dataDir, "system");

???//syncDir指向/data/system/registered_service目錄

??? FilesyncDir = new File(systemDir, "registered_services");

??? //下面這個(gè)文件指向syncDir目錄下的android.accounts.AccountAuthenticator.xml

???mPersistentServicesFile = new AtomicFile(new File(syncDir,

????????????????????????????????????????? interfaceName+ ".xml"));

??? //生成服務(wù)信息

???generateServicesMap();

?

??? finalBroadcastReceiver receiver = new BroadcastReceiver() {

??????public void onReceive(Context context1, Intent intent) {

?????????generateServicesMap();

???????? }

??? };

??? //注冊(cè)Package安裝、卸載和更新等廣播監(jiān)聽(tīng)者

???mReceiver = new AtomicReference<BroadcastReceiver>(receiver);

?? ?IntentFilter intentFilter = newIntentFilter();

???intentFilter.addAction(Intent.ACTION_PACKAGE_ADDED);

???intentFilter.addAction(Intent.ACTION_PACKAGE_CHANGED);

???intentFilter.addAction(Intent.ACTION_PACKAGE_REMOVED);

???intentFilter.addDataScheme("package");

???mContext.registerReceiver(receiver, intentFilter);

?? ?IntentFilter sdFilter = new IntentFilter();

???sdFilter.addAction(Intent.ACTION_EXTERNAL_APPLICATIONS_AVAILABLE);

???sdFilter.addAction(Intent.ACTION_EXTERNAL_APPLICATIONS_UNAVAILABLE);

???mContext.registerReceiver(receiver, sdFilter);

}

void generateServicesMap() {

?? //獲取PackageManager接口，用來(lái)和PackageManagerService交互

??PackageManager pm = mContext.getPackageManager();

??ArrayList<ServiceInfo<V>> serviceInfos = newArrayList<ServiceInfo<V>>();

?? /*

?? 在本例中，查詢(xún)PKMS中滿足Intent Action為"android.accounts.AccountAuthenticator"

?? 的服務(wù)信息。由以下代碼可知，這些信息指的是Service中聲明的MetaData信息

?? */

??List<ResolveInfo> resolveInfos = pm.queryIntentServices(

???????????????new Intent(mInterfaceName),PackageManager.GET_META_DATA);

?

?? for(ResolveInfo resolveInfo : resolveInfos) {

????? try {

??????????/*

??????????? 調(diào)用parserServiceInfo函數(shù)解析從PKMS中獲得的MetaData信息，該函數(shù)

?????????? ?返回的是一個(gè)模板類(lèi)對(duì)象。就本例而言，這個(gè)函數(shù)返回一個(gè)

??????????? ServiceInfo<AccountAuthenticator>類(lèi)型的對(duì)象

??????????*/

??????????ServiceInfo<V> info = parseServiceInfo(resolveInfo);

??????????serviceInfos.add(info);

???????? }

???? ?}

?

???synchronized (mServicesLock) {

?????? if(mPersistentServices == null)

???????????readPersistentServicesLocked();

??????mServices = Maps.newHashMap();

??????StringBuilder changes = new StringBuilder();

?????? ......//檢查mPersistentServices保存的服務(wù)信息和當(dāng)前從PKMS中取出來(lái)的PKMS

????? //信息，判斷是否有變化，如果有變化，需要通知監(jiān)聽(tīng)者。讀者可自行閱讀這段代碼，

???? //注意其中uid的作用

???????mPersistentServicesFileDidNotExist = false;

???? }

?}

private ServiceInfo<V>parseServiceInfo(ResolveInfo service)

?????????? ??????????throws XmlPullParserException, IOException {

??android.content.pm.ServiceInfo si = service.serviceInfo;

??ComponentName componentName = new ComponentName(si.packageName, si.name);

?

??PackageManager pm = mContext.getPackageManager();

?

??XmlResourceParser parser = null;

?? try {

??????? //解析MetaData信息

???????parser = si.loadXmlMetaData(pm, mMetaDataName);

???????AttributeSet attrs = Xml.asAttributeSet(parser);

?

??????? inttype;

???????......

?

????? StringnodeName = parser.getName();

????? //調(diào)用子類(lèi)實(shí)現(xiàn)的parseServiceAttributes得到一個(gè)真實(shí)的對(duì)象，在本例中它是

????? //AuthenticatorDescription。注意，傳遞給parseServiceAttributes的第一個(gè)

????? //參數(shù)代表MetaData中的resource信息。詳細(xì)內(nèi)容見(jiàn)下文的圖例

???? V v=parseServiceAttributes(

???????????????????? pm.getResourcesForApplication(si.applicationInfo),

????????????????????si.packageName, attrs);

?

??? finalandroid.content.pm.ServiceInfo serviceInfo = service.serviceInfo;

??? finalApplicationInfo applicationInfo = serviceInfo.applicationInfo;

??? finalint uid = applicationInfo.uid;

??? returnnew ServiceInfo<V>(v, componentName, uid);

? ?} ...... finally {

???????????if (parser != null) parser.close();

??? }

?}

提示uid是在為PackageManagerService解析APK文件時(shí)賦予APK的。讀者不妨自行閱讀frameworks/base/services/java/com/android/server/pm/Settings.java中的newUserIdLPw函數(shù)。

public AccountManagerService(Context context,PackageManager packageManager,

???????????IAccountAuthenticatorCache authenticatorCache) {

?

??? mContext= context;

???mPackageManager = packageManager;

?

??synchronized (mCacheLock) {

????? //此數(shù)據(jù)庫(kù)文件對(duì)應(yīng)為/data/system/accounts.db

?????mOpenHelper = new DatabaseHelper(mContext);

?? }

?

??mMessageThread = new HandlerThread("AccountManagerService");

??mMessageThread.start();

??mMessageHandler = new MessageHandler(mMessageThread.getLooper());

?

??mAuthenticatorCache = authenticatorCache;

?? //為AccountAuthenticatorCache設(shè)置一個(gè)監(jiān)聽(tīng)者，一旦AAS服務(wù)發(fā)生變化，

??//AccountManagerService需要做對(duì)應(yīng)處理

??mAuthenticatorCache.setListener(this, null /* Handler */);

?

??sThis.set(this);

?? //監(jiān)聽(tīng)ACTION_PACKAGE_REMOVED廣播

??IntentFilter intentFilter = new IntentFilter();

??intentFilter.addAction(Intent.ACTION_PACKAGE_REMOVED);

??intentFilter.addDataScheme("package");

??mContext.registerReceiver(new BroadcastReceiver() {

?? publicvoid onReceive(Context context1, Intent intent) {

???????purgeOldGrants();

???? }

?? },intentFilter);

? ?/*

??? accounts.db數(shù)據(jù)庫(kù)中有一個(gè)grants表，用于存儲(chǔ)授權(quán)信息，該信息用于保存哪些Package

?? ?有權(quán)限獲取賬戶信息。下面的函數(shù)將根據(jù)grants表中的數(shù)據(jù)查詢(xún)PKMS，以判斷這些

?? ?Package是否還存在。如果系統(tǒng)中已經(jīng)不存在這些Package，則grants表需要更新

? */

? ?purgeOldGrants();

?? /*

??accounts.db中有一個(gè)accounts表，該表中存儲(chǔ)了賬戶類(lèi)型和賬戶名。其中，賬戶類(lèi)型

?? 就是AuthenticatorDescription中的accountType，它和具體應(yīng)用有關(guān)。下面這個(gè)

?? 函數(shù)將比較accounts表中的內(nèi)容與AccountAuthenticatorCache中服務(wù)的信息，如果

?? AccountAuthenticatorCache已經(jīng)不存在對(duì)應(yīng)賬戶類(lèi)型的服務(wù)，則需要?jiǎng)h除accounts表

?? 中的對(duì)應(yīng)項(xiàng)

? */

??validateAccountsAndPopulateCache();

?}

public AccountManagerFuture<Bundle>addAccount(

?? finalString accountType,

?? finalString authTokenType,

?? finalString[] requiredFeatures,

?? finalBundle addAccountOptions,

?? finalActivity activity,

?? AccountManagerCallback<Bundle>callback,

?? Handlerhandler)

public AccountManagerFuture<Bundle>addAccount(final String accountType,

???? finalString authTokenType, final String[] requiredFeatures,

???? finalBundle addAccountOptions, final Activity activity,

????AccountManagerCallback<Bundle> callback, Handler handler) {

??? if(accountType == null) //accountType不能為null

??????????? thrownew IllegalArgumentException("accountType is null");

?? finalBundle optionsIn = new Bundle();

?? if(addAccountOptions != null)//保存客戶端傳入的addAccountOptions

??????optionsIn.putAll(addAccountOptions);

?

??optionsIn.putString(KEY_ANDROID_PACKAGE_NAME,

??????????????????????? mContext.getPackageName());

??? //構(gòu)造一個(gè)匿名類(lèi)對(duì)象，該類(lèi)繼承自AmsTask，并實(shí)現(xiàn)了doWork函數(shù)。addAccount返回前

??? //將調(diào)用該對(duì)象的start函數(shù)

??? returnnew AmsTask(activity, handler, callback) {

????? publicvoid doWork() throws RemoteException {

???????????//mService用于和AccountManagerService通信

???????????mService.addAcount(mRespo