ContentProvider源码分析（原）
一、前言
getContentResolver().delete();
1、通过getContentResolver()得到需要的ContentProvider对象；
2、通过delete()操作，将ContentProvider中的数据删除；
下面我们就开启此次漫长的旅程。
二、getContentResolver
看标题，我们是要得到一个ContentResolver的对象，这就产生了两个疑问：1、ContentResolver对象与ContentProvider有什么关系？
2、我们是如何得到ContentProvider中的内容呢？
为了解答这两个问题，我们需要从代码的最源头开始分析：
2.1、ContentResolver与ContentProvider的关系
先来看看得到ContentResolver的过程： @ContextImpl.java
public ContentResolver getContentResolver() {
return mContentResolver;
}
final void init(Resources resources, ActivityThread mainThread, UserHandle user) {
mPackageInfo = null;
mBasePackageName = null;
mResources = resources;
mMainThread = mainThread;
//mContentResolver被初始化为ApplicationContentResolver对象
mContentResolver = new ApplicationContentResolver(this, mainThread, user);
mUser = user;
}
private static final class ApplicationContentResolver extends ContentResolver {
public ApplicationContentResolver( Context context, ActivityThread mainThread, UserHandle user) { }
protected IContentProvider acquireProvider(Context context, String auth) { }
protected IContentProvider acquireExistingProvider(Context context, String auth) { }
public boolean releaseProvider(IContentProvider provider) { }
protected IContentProvider acquireUnstableProvider(Context c, String auth) { }
public boolean releaseUnstableProvider(IContentProvider icp) { }
public void unstableProviderDied(IContentProvider icp) { }
}
@ContentResolver.java
public abstract class ContentResolver { }
那么我们是如何最终得到ContentProvider的呢？
2.2、如何通过ContentResolver得到ContentProvider
下面我们来解答第二个疑问，我们是 如何通过ContentResolver去查询到ContentProvider中的内容呢？虽然我们知道这两者从继承关系上并没有什么联系，但是ContentResolver的内部却出现了我们熟悉的一些方法，包括：
public final Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {}
public final int delete(Uri url, String where, String[] selectionArgs){}
public final int update(Uri uri, ContentValues values, String where, String[] selectionArgs) {}
public final Uri insert(Uri url, ContentValues values){}
回到最初的调用地点，当我们需要通过ContentProvider去delete一项数据时，就会调用getContentResolver().delete()方法，上面分析道， getContentResolver()得到的就是ApplicationContentResolver的对象，而ApplicationContentResolver又继承自ContentResolver。因此，delete的操作就落在ContentResolver中：
@ContentResolver.java
public final int delete(Uri url, String where, String[] selectionArgs)
{
IContentProvider provider = acquireProvider(url);
try {
int rowsDeleted = provider.delete(url, where, selectionArgs);
} catch (RemoteException e) {
} finally {
}
}
public final IContentProvider acquireProvider(Uri uri) {
//安全确认
if (!SCHEME_CONTENT.equals(uri.getScheme())) {
return null;
}
final String auth = uri.getAuthority();
if (auth != null) {
//继续调用
return acquireProvider(mContext, auth);
}
return null;
}
protected abstract IContentProvider acquireProvider(Context c, String name);
@ContextImpl.java
private static final class ApplicationContentResolver extends ContentResolver {
//果然找到了acquireProvider方法
protected IContentProvider acquireProvider(Context context, String auth) {
return mMainThread.acquireProvider(context, auth, mUser.getIdentifier(), true);
}
}
那么，这个mMainThread是哪里来的呢？
接下来所介绍的流程，比较复杂，各位看好了。
2.3、寻找mMainThread对象来历
在ActivityThread中创建一个Activity之后，就会调用ActivityThread中的createBaseContextForActivity()方法，为当前的Activity创建Context对象和mMainThread对象： @ActivityThread.java
private Context createBaseContextForActivity(ActivityClientRecord r, final Activity activity) {
//这里就是要创建Context对象的地方
ContextImpl appContext = new ContextImpl();
//并把当前ActivityThread对象传递给ContextImpl的init方法中
appContext.init(r.packageInfo, r.token, this);
}
@ContextImpl.java
//这里的mainThread就是ActivityThread对象
final void init(LoadedApk packageInfo, IBinder activityToken, ActivityThread mainThread) {
init(packageInfo, activityToken, mainThread, null, null, Process.myUserHandle());
}
final void init(LoadedApk packageInfo, IBinder activityToken, ActivityThread mainThread, Resources container, String basePackageName, UserHandle user){
//mMainThread就是ActivityThread对象
mMainThread = mainThread;
mContentResolver = new ApplicationContentResolver(this, mainThread, user);
}
ActivityThread.acquireProvider();
@ActivityThread.java
public final IContentProvider acquireProvider( Context c, String auth, int userId, boolean stable) {
final IContentProvider provider = acquireExistingProvider(c, auth, userId, stable);
if (provider != null) {
return provider;
}
IActivityManager.ContentProviderHolder holder = null;
try {
holder = ActivityManagerNative.getDefault().getContentProvider( getApplicationThread(), auth, userId, stable);
} catch (RemoteException ex) {
}
holder = installProvider(c, holder, holder.info, true , holder.noReleaseNeeded, stable);
return holder.provider;
}
我们假设当前没有ContactsProvider的缓存，那么将会通过ActivityManagerNative.getDefault().getContentProvider()创建该provider，下面我们来分析这个创建的过程。
2.4、ActivityThread创建ContentProvider的过程。
前面说过，ActivityThread创建ContentProvider是通过以下方式实现的： ActivityManagerNative.getDefault().getContentProvider( getApplicationThread(), auth, userId, stable);
这个过程可以分为两步：
1、我们来看通过ActivityManagerNative.getDefault()所得到的对象；
2、我们再来分析这个对象的getContentProvider方法。
2.4.1、ActivityManagerNative对象。
我们先介绍一下ActivityManagerService服务。当系统启动后，在SystemServer中就会将一些重要的Server启动起来，其中就包括ActivityManagerService：
@SystemServer.java
public void run() {
//启动ActivityManagerService
context = ActivityManagerService.main(factoryTest);
//注册ActivityManagerService
ActivityManagerService.setSystemProcess();
}
@ActivityManagerService.java
public static void setSystemProcess() {
try {
ActivityManagerService m = mSelf;
//将自己注册为“activity”的Server
ServiceManager.addService("activity", m, true);
ServiceManager.addService("meminfo", new MemBinder(m));
ServiceManager.addService("gfxinfo", new GraphicsBinder(m));
ServiceManager.addService("dbinfo", new DbBinder(m));
} catch (PackageManager.NameNotFoundException e) {
}
}
public final class ActivityManagerService extends ActivityManagerNative implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {}
这样我们就对ActivityManagerNative的结构有了大致的了解， 根据Binder通讯机制，如果我们跨进程去请求ActivityManagerService的服务时，就会调用他的asBinder()方法，并把他的IBinder对象返回给客户端使用。
接着我们上面的分析，我们在2.4节中把创建ContentProvider分为两步， 第一步就是得到ActivityManagerNative.getDefault()对象，现在我们来看源码：
@ActivityManagerNative.java
static public IActivityManager getDefault() {
return gDefault.get();
}
private static final Singleton gDefault = new Singleton() {
protected IActivityManager create() {
IBinder b = ServiceManager.getService("activity");
IActivityManager am = asInterface(b);
return am;
}
};
1、通过getService("activity")得到ActivityManagerService的远程Binder；
2、利用得到的Biner对象通过asInterface()方法，得到这个服务的远程代理；
对于得到Binder对象，这是由Binder系统决定的，我们无需多看，我们来看一下如何通过Binder得到服务的远程代理：
static public IActivityManager asInterface(IBinder obj) {
if (obj == null) {
return null;
}
IActivityManager in = (IActivityManager)obj.queryLocalInterface(descriptor);
if (in != null) {
return in;
}
return new ActivityManagerProxy(obj);
}
ActivityManagerNative.getDefault().getContentProvider( getApplicationThread(), auth, userId, stable);
ActivityManagerProxy.getContentProvider(getApplicationThread(), auth, userId, stable);;
2.4.2、代理对象的getContentProvider操作
这一步当然是在ActivityManagerProxy类中发生的： @ActivityManagerNative.java
class ActivityManagerProxy implements IActivityManager{
public ContentProviderHolder getContentProvider(IApplicationThread caller,
String name, int userId, boolean stable) throws RemoteException {
Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IActivityManager.descriptor);
data.writeStrongBinder(caller != null ? caller.asBinder() : null);
data.writeString(name);
data.writeInt(userId);
data.writeInt(stable ? 1 : 0);
//向ActivityManagerNative发送请求
mRemote.transact(GET_CONTENT_PROVIDER_TRANSACTION, data, reply, 0);
reply.readException();
int res = reply.readInt();
ContentProviderHolder cph = null;
if (res != 0) {
cph = ContentProviderHolder.CREATOR.createFromParcel(reply);
}
data.recycle();
reply.recycle();
return cph;
}
}
而ActivityManagerNative需要在onTransact()中去接收请求：
@ActivityManagerNative.java
public abstract class ActivityManagerNative extends Binder implements IActivityManager{
//处理各种请求
public boolean onTransact(int code, Parcel data, Parcel reply, int flags) throws RemoteException {
switch (code) {
case GET_CONTENT_PROVIDER_TRANSACTION: {
data.enforceInterface(IActivityManager.descriptor);
IBinder b = data.readStrongBinder();
IApplicationThread app = ApplicationThreadNative.asInterface(b);
String name = data.readString();
int userId = data.readInt();
boolean stable = data.readInt() != 0;
//调用ActivityManagerService的getContentProvider方法
ContentProviderHolder cph = getContentProvider(app, name, userId, stable);
reply.writeNoException();
if (cph != null) {
reply.writeInt(1);
cph.writeToParcel(reply, 0);
} else {
reply.writeInt(0);
}
return true;
}
}
}
}
@ActivityManagerService.java
public final ContentProviderHolder getContentProvider( IApplicationThread caller, String name, int userId, boolean stable) {
return getContentProviderImpl(caller, name, null, stable, userId);
}
private final ContentProviderHolder getContentProviderImpl(IApplicationThread caller, String name, IBinder token, boolean stable, int userId) {
ContentProviderRecord cpr;
ContentProviderConnection conn = null;
ProviderInfo cpi = null;
synchronized(this) {
//查询缓存中是否已经存在该ContentProviderRecord
cpr = mProviderMap.getProviderByName(name, userId);
boolean providerRunning = cpr != null;
if (providerRunning) {
//如果该provider已经被运行过
//得到该ContentProviderRecord的ProviderInfo
cpi = cpr.info;
if (r != null && cpr.canRunHere(r)) {
//直接将ContentProviderHolder传给客户端即可
ContentProviderHolder holder = cpr.newHolder(null);
//清空其provider，由客户端自己去初始化provider的对象
holder.provider = null;
return holder;
}
}
if (!providerRunning) {
//当前没有运行
//加载该provider的包，得到ProviderInfo
cpi = AppGlobals.getPackageManager().resolveContentProvider(name, STOCK_PM_FLAGS | PackageManager.GET_URI_PERMISSION_PATTERNS, userId);
//为当前provider创建ContentProviderRecord
ComponentName comp = new ComponentName(cpi.packageName, cpi.name);
cpr = mProviderMap.getProviderByClass(comp, userId);
//缓存当前的ContentProviderRecord
mProviderMap.putProviderByName(name, cpr);
conn = incProviderCountLocked(r, cpr, token, stable);
}
}
//将ContentProviderHolder传给客户端
return cpr != null ? cpr.newHolder(conn) : null;
}
1、通过ContentProviderRecord.info可以得到当前provider的详细信息，包括该provider的authority、readPermission、writePermission、uriPermissionPatterns等重要信息；
2、可以通过ContentProviderRecord.newHolder()方法，生成一个针对当前provider的详细信息，我们需要把这些信息打包为Holder传递给ActivityThread使用。
我们再回到ActivityThread中的acquireProvider()里面：
public final IContentProvider acquireProvider( Context c, String auth, int userId, boolean stable) {
final IContentProvider provider = acquireExistingProvider(c, auth, userId, stable);
IActivityManager.ContentProviderHolder holder = null;
try {
//得到ContentProviderHolder对象
holder = ActivityManagerNative.getDefault().getContentProvider( getApplicationThread(), auth, userId, stable);
} catch (RemoteException ex) {
}
//用provider信息去初始化当前的provider
holder = installProvider(c, holder, holder.info, true , holder.noReleaseNeeded, stable);
//得到provider对象
return holder.provider;
}
private IActivityManager.ContentProviderHolder installProvider(Context context, IActivityManager.ContentProviderHolder holder, ProviderInfo info, boolean noisy, boolean noReleaseNeeded, boolean stable) {
ContentProvider localProvider = null;
IContentProvider provider;
if (holder == null || holder.provider == null) {
//当前客户端没有得到过该provider，因此需要获得该provider远程代理
Context c = null;
ApplicationInfo ai = info.applicationInfo;
if (context.getPackageName().equals(ai.packageName)) {
//如果要获得的provider就在当前发出请求的客户端
c = context;
} else if (mInitialApplication != null && mInitialApplication.getPackageName().equals(ai.packageName)) {
c = mInitialApplication;
} else {
try {
//为要创建的provider创建Context对象
c = context.createPackageContext(ai.packageName, Context.CONTEXT_INCLUDE_CODE);
} catch (PackageManager.NameNotFoundException e) {
}
}
try {
final java.lang.ClassLoader cl = c.getClassLoader();
//载入provider的类
localProvider = (ContentProvider)cl.loadClass(info.name).newInstance();
//得到该provider的IContentProvider对象
provider = localProvider.getIContentProvider();
localProvider.attachInfo(c, info);
} catch (java.lang.Exception e) {
}
} else {
//如果已经为该客户端创建过相应的provider，直接返回即可
provider = holder.provider;
}
IActivityManager.ContentProviderHolder retHolder;
synchronized (mProviderMap) {
IBinder jBinder = provider.asBinder();
//重新构建ContentProviderHolder类型的retHolder
if (localProvider != null) {
ComponentName cname = new ComponentName(info.packageName, info.name);
ProviderClientRecord pr = mLocalProvidersByName.get(cname);
if (pr != null) {
provider = pr.mProvider;
} else {
//得到ContentProvider的远程代理对象
holder = new IActivityManager.ContentProviderHolder(info);
holder.provider = provider;
holder.noReleaseNeeded = true;
pr = installProviderAuthoritiesLocked(provider, localProvider, holder);
mLocalProviders.put(jBinder, pr);
mLocalProvidersByName.put(cname, pr);
}
retHolder = pr.mHolder;
} else {
ProviderRefCount prc = mProviderRefCountMap.get(jBinder);
if (prc != null) {
if (!noReleaseNeeded) {
incProviderRefLocked(prc, stable);
try {
ActivityManagerNative.getDefault().removeContentProvider( holder.connection, stable);
} catch (RemoteException e) {
}
}
} else {
ProviderClientRecord client = installProviderAuthoritiesLocked(provider, localProvider, holder);
if (noReleaseNeeded) {
prc = new ProviderRefCount(holder, client, 1000, 1000);
} else {
prc = stable
? new ProviderRefCount(holder, client, 1, 0)
: new ProviderRefCount(holder, client, 0, 1);
}
mProviderRefCountMap.put(jBinder, prc);
}
retHolder = prc.holder;
}
}
return retHolder;
}
然后我们再回到ActivityThread中的acquireProvider():
public final IContentProvider acquireProvider( Context c, String auth, int userId, boolean stable) {
final IContentProvider provider = acquireExistingProvider(c, auth, userId, stable);
IActivityManager.ContentProviderHolder holder = null;
try {
//得到ContentProviderHolder对象
holder = ActivityManagerNative.getDefault().getContentProvider( getApplicationThread(), auth, userId, stable);
} catch (RemoteException ex) {
}
//用provider信息去初始化当前的provider
holder = installProvider(c, holder, holder.info, true , holder.noReleaseNeeded, stable);
//将得到provider代理对象返回给客户端调用
return holder.provider;
}
经过上面的分析，我们从最初的getContentResolver()一步步的分析，经过ContextImpl、ActivityThread、ActivityManagerNative、ActivityManagerService，最终得到了ContentProvider的代理对象。
三、ContentProvider调用分析
在上面一节中我们对getContentResolver()的过程进行分析，发现这样操作的结果不仅可以载入需要的ContentProvider（如果当前ContentProvider还没有被载入），并且调用了该ContentProvider的getIContentProvider()方法。这一节我们就要从这个方法入手，看看如何通过这个方法得到ContentProvider对象，又如何通过该对象传递对数据库的操作。我们先来看一下通过getIContentProvider()方法得到的究竟是什么对象。
@ContentProvider.java
public IContentProvider getIContentProvider() {
return mTransport;
}
private Transport mTransport = new Transport();
class Transport extends ContentProviderNative {
ContentProvider getContentProvider() { }
public String getProviderName() { }
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder, ICancellationSignal cancellationSignal) { }
public Uri insert(Uri uri, ContentValues initialValues) { }
public ContentProviderResult[] applyBatch(ArrayList operations) throws OperationApplicationException { }
public int delete(Uri uri, String selection, String[] selectionArgs) { }
public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) { }
}
public int delete(Uri uri, String selection, String[] selectionArgs) {
enforceWritePermission(uri);
return ContentProvider.this.delete(uri, selection, selectionArgs);
}
public abstract int delete(Uri uri, String selection, String[] selectionArgs);
我们此时来看一下ContentProvider本身提供了哪些重要的方法：
public abstract class ContentProvider implements ComponentCallbacks2 {
private Transport mTransport = new Transport();
//构造函数
public ContentProvider() { }
//权限相关操作
protected final void setReadPermission(String permission) { }
public final String getReadPermission() { }
protected final void setWritePermission(String permission) { }
public final String getWritePermission() { }
//增、删、改、查操作。
public abstract Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder);
public abstract Uri insert(Uri uri, ContentValues values);
public abstract int delete(Uri uri, String selection, String[] selectionArgs);
public abstract int update(Uri uri, ContentValues values, String selection, String[] selectionArgs);
public IContentProvider getIContentProvider() { }
public ContentProviderResult[] applyBatch(ArrayList operations) throws OperationApplicationException { }
}
此时我们结合Transport来分析不难发现，这个Transport对象作为ContentProvider的代理，可以对此对象发起各项请求。该代理得到请求后，就会把请求“转发”给ContentProvider本身。
结合上一节我们分析的内容，我们可以总结如下：
我们在应用层调用getContentResolver().delete()的操作，将会调用到ContentResolver对象的delete操作，而ContentResolver对象就相当于通过getIContentProvider()得到的Transport对象，而Transport对象作为ContentProvider的代理将会把各项请求转移到ContentProvider中，因此就调用到ContentProvider的delete方法。
getContentResolver==>ContentResolver==>Transport==>ContentProvider
四、ContentProvider到ContactsProvider
4.1、ContactsProvider综览
经过上面的过程，我们把操作转移到了ContentProvider中，接下来我们需要借助具体的provider来继续分析， 我们挑选联系人数据库（ContactsProvider）作为示例来研究。联系人数据库源码位于\packages\providers\ContactsProvider\中，我们先来看一下他的AndroidManifest.xml文件：
@AndroidManifest.xml
4.2、ContactsProvider结构
ContactsProvider结构中涉及到五个重要的类：ContentProvider、SQLiteTransactionListener、AbstractContactsProvider、ContactsProvider2、ProfileProvider。下面我们先简单说一下他们的关系。ContactsProvider在ContentProvider的基础上与SQLiteTransactionListener结合共同组件了AbstractContactsProvider，这是ContactsProvider最基础的类，然后在AbstractContactsProvider的基础上，扩展出来了ContactsProvider2和ProfileProvider这两个类，如下图所示：
接下来我们来分别介绍这五个类的作用。
4.2.1、ContactsProvider
这个不用多说，是系统提供的ContactsProvider架构，里面遗留了对数据库操作的接口，需要子类去实现。4.2.2、SQLiteTransactionListener
这是一个接口，里面内容也比较简单，只有3个方法： public interface SQLiteTransactionListener {
/**
* Called immediately after the transaction begins.
*/
void onBegin();
/**
* Called immediately before commiting the transaction.
*/
void onCommit();
/**
* Called if the transaction is about to be rolled back.
*/
void onRollback();
}
4.2.3、AbstractContactsProvider
这是ContactsProvider结构中最底层的类，我们来看一下他内部主要的方法： public abstract class AbstractContactsProvider extends ContentProvider implements SQLiteTransactionListener {
public SQLiteOpenHelper getDatabaseHelper() { }
public Uri insert(Uri uri, ContentValues values) { }
public int delete(Uri uri, String selection, String[] selectionArgs) { }
public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) { }
public ContentProviderResult[] applyBatch(ArrayList operations) { }
private ContactsTransaction startTransaction(boolean callerIsBatch) { }
private void endTransaction(boolean callerIsBatch) { }
protected abstract SQLiteOpenHelper getDatabaseHelper(Context context);
protected abstract ThreadLocal getTransactionHolder();
protected abstract Uri insertInTransaction(Uri uri, ContentValues values);
protected abstract int deleteInTransaction(Uri uri, String selection, String[] selectionArgs);
protected abstract int updateInTransaction(Uri uri, ContentValues values, String selection, String[] selectionArgs);
protected abstract void notifyChange();
}
public int delete(Uri uri, String selection, String[] selectionArgs) {
//开始事务操作
ContactsTransaction transaction = startTransaction(false);
try {
//用事务进行delete的操作
int deleted = deleteInTransaction(uri, selection, selectionArgs);
if (deleted > 0) {
transaction.markDirty();
}
transaction.markSuccessful(false);
return deleted;
} finally {
endTransaction(false);
}
}
protected abstract int deleteInTransaction(Uri uri, String selection, String[] selectionArgs);
到这里我们发现，在AbstractContactsProvider中把insert、delete、update的操作转换成了事务的处理方式XXXInTransaction，并且把具体的实现留给了子类，这里的子类就是ContactsProvider2和ProfileProvider。也就是说， AbstractContactsProvider的作用就是把对数据库的操作转换成事务的处理方式，至于具体的事务操作，需要在其子类中实现。
另外，我们注意到，所转换的只是insert、delete、update操作，而没有query的操作，也就是说，在ContentProvider中的query操作直接遗留给了子类的子类去实现，而跨过了AbstractContactsProvider的转换。这就说明， query的操作并不需要转换成事务的处理方式。
4.2.4、ProfileProvider
我们现在来看ProfileProvider的结构： public class ProfileProvider extends AbstractContactsProvider {
public Cursor query(Uri uri,String[] projection,String selection,String[] selectionArgs,String sortOrder){}
protected Uri insertInTransaction(Uri uri, ContentValues values){}
protected int updateInTransaction(Uri uri, ContentValues values, String selection, String[] selectionArgs) {}
protected int deleteInTransaction(Uri uri, String selection, String[] selectionArgs){}
public void onBegin() { }
public void onCommit() { }
public void onRollback() { }
}
这个问题我们待会儿就会明白。
4.2.5、ContactsProvider2
这是ContactsProvider中最重要也是最上层的类，当初我们在AndroidManifest中只对他进行了注册。我们来看一下他里面重要的方法：
public class ContactsProvider2 extends AbstractContactsProvider implements OnAccountsUpdateListener {
public Cursor query(Uri uri,String[] projection,String selection,String[] selectionArgs,String sortOrder) {}
public int delete(Uri uri, String selection, String[] selectionArgs) {}
public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {}
public Uri insert(Uri uri, ContentValues values) {}
protected Uri insertInTransaction(Uri uri, ContentValues values) {}
protected int updateInTransaction(Uri uri, ContentValues values, String selection, String[] selectionArgs) {}
protected int deleteInTransaction(Uri uri, String selection, String[] selectionArgs) {}
}
与ProfileProvider类似，他也提供了完整的数据访问、修改能力。
五、ContactsProvider与SQLite
我们需要明白一点，ContentProvider的底层仍然依靠SQLite来实现的，ContentProvider只是将SQLite的操作进行了封装，更容易操作和理解。
在ContactsProvider的底层设计上，ContactsDatabaseHelper承担着与SQLite直接沟通的角色，在此之上又有差异化扩展了ProfileDatabaseHelper这个类。因此可以认为，在ContactsProvider的底层有两个与SQLite的帮助类。先来看一下他们的结构：
public class ProfileDatabaseHelper extends ContactsDatabaseHelper {}
public class ContactsDatabaseHelper extends SQLiteOpenHelper {}
这两个SQLiteOpenHelper类均是在ContactsProvider2的onCreate()时被初始化的：
public boolean onCreate() {
super.onCreate();
return initialize();
}
private boolean initialize() {
//初始化ContactsDatabaseHelper
mContactsHelper = getDatabaseHelper(getContext());
mDbHelper.set(mContactsHelper);
//初始化ProfileDatabaseHelper
mProfileHelper = mProfileProvider.getDatabaseHelper(getContext());
return true;
}
protected ContactsDatabaseHelper getDatabaseHelper(final Context context) {
return ContactsDatabaseHelper.getInstance(context);
}
@ContactsDatabaseHelper.java
public static synchronized ContactsDatabaseHelper getInstance(Context context) {
if (sSingleton == null) {
//new出一个ContactsDatabaseHelper完成初始化
sSingleton = new ContactsDatabaseHelper(context, DATABASE_NAME, true);
}
return sSingleton;
}
protected ProfileDatabaseHelper getDatabaseHelper(Context context) {
return ProfileDatabaseHelper.getInstance(context);
}
public static synchronized ProfileDatabaseHelper getInstance(Context context) {
if (sSingleton == null) {
//new出一个ProfileDatabaseHelper完成初始化
sSingleton = new ProfileDatabaseHelper(context, DATABASE_NAME, true);
}
return sSingleton;
}
既然SQLiteOpenHelper存在两个，配套的，应该就有两个ContentProvider去操作这两个SQLiteOpenHelper，事实确实如此，在这两个SQLite操作类之上，分别搭建了ProfileProvider与ContactsProvider2这两个与ContentProvider相关的类，也就是说，这四者的对应关系类似与下图：
下面我们借助一次delete()操作来看看这两对数据库的操作流向。
5.1、仍然继续delete()
我们不妨再次回顾一下，当我们进行delete操作时，我们调用getContentResolver最终将会调用到ContentProvider中的delete方法，进而调用到ContactsProvider2中的delete方法： @ContactsProvider2.java
public int delete(Uri uri, String selection, String[] selectionArgs) {
waitForAccess(mWriteAccessLatch);
//权限管理
enforceSocialStreamWritePermission(uri);
//查看是否需要放到ProfileProvider中处理
if (mapsToProfileDb(uri)) {
switchToProfileMode();
//在ProfileProvider中处理
return mProfileProvider.delete(uri, selection, selectionArgs);
} else {
switchToContactMode();
//回到父类中处理delete操作
return super.delete(uri, selection, selectionArgs);
}
}
private boolean mapsToProfileDb(Uri uri) {
return sUriMatcher.mapsToProfile(uri);
}
@ContactsProvider2.java
static {
final UriMatcher matcher = sUriMatcher;
matcher.addURI(ContactsContract.AUTHORITY, "contacts", CONTACTS);
matcher.addURI(ContactsContract.AUTHORITY, "contacts/#", CONTACTS_ID);
matcher.addURI(ContactsContract.AUTHORITY, "contacts/#/data", CONTACTS_ID_DATA);
matcher.addURI(ContactsContract.AUTHORITY, "contacts/#/entities", CONTACTS_ID_ENTITIES);
matcher.addURI(ContactsContract.AUTHORITY, "contacts/#/suggestions", AGGREGATION_SUGGESTIONS);
matcher.addURI(ContactsContract.AUTHORITY, "contacts/#/suggestions/*", AGGREGATION_SUGGESTIONS);
matcher.addURI(ContactsContract.AUTHORITY, "contacts/#/photo", CONTACTS_ID_PHOTO);
matcher.addURI(ContactsContract.AUTHORITY, "contacts/#/display_photo", CONTACTS_ID_DISPLAY_PHOTO);
matcher.addURI(ContactsContract.AUTHORITY, "contacts/#/stream_items", CONTACTS_ID_STREAM_ITEMS);
matcher.addURI(ContactsContract.AUTHORITY, "contacts/filter", CONTACTS_FILTER);
matcher.addURI(ContactsContract.AUTHORITY, "contacts/filter/*", CONTACTS_FILTER);
matcher.addURI(ContactsContract.AUTHORITY, "contacts/lookup/*", CONTACTS_LOOKUP);
matcher.addURI(ContactsContract.AUTHORITY, "contacts/lookup/*/data", CONTACTS_LOOKUP_DATA);
matcher.addURI(ContactsContract.AUTHORITY, "contacts/lookup/*/photo", CONTACTS_LOOKUP_PHOTO);
matcher.addURI(ContactsContract.AUTHORITY, "contacts/lookup/*/#", CONTACTS_LOOKUP_ID);
matcher.addURI(ContactsContract.AUTHORITY, "contacts/lookup/*/#/data", CONTACTS_LOOKUP_ID_DATA);
matcher.addURI(ContactsContract.AUTHORITY, "contacts/lookup/*/#/photo", CONTACTS_LOOKUP_ID_PHOTO);
matcher.addURI(ContactsContract.AUTHORITY, "contacts/lookup/*/display_photo", CONTACTS_LOOKUP_DISPLAY_PHOTO);
//......
}
下面我们分别看这两种情况具体的操作。
5.2、ContactsProvider2的操作
我们先来分析这个数据流操作，再去分析ProfileProvider操作。也就是说我们需要switchToContactMode()：
private void switchToContactMode() {
//将mDbHelper切换到mContactsHelper，也就是ContactsDatabaseHelper
mDbHelper.set(mContactsHelper);
mTransactionContext.set(mContactTransactionContext);
mAggregator.set(mContactAggregator);
mPhotoStore.set(mContactsPhotoStore);
mInProfileMode.set(false);
}
@AbstractContactsProvider.java
public int delete(Uri uri, String selection, String[] selectionArgs) {
ContactsTransaction transaction = startTransaction(false);
try {
int deleted = deleteInTransaction(uri, selection, selectionArgs);
transaction.markSuccessful(false);
return deleted;
} finally {
endTransaction(false);
}
}
protected abstract int deleteInTransaction(Uri uri, String selection, String[] selectionArgs);
protected int deleteInTransaction(Uri uri, String selection, String[] selectionArgs) {
//得到SQLiteOpenHelper，当前是ContactsDatabaseHelper
final SQLiteDatabase db = mDbHelper.get().getWritableDatabase();
//根据当前uri匹配结果
final int match = sUriMatcher.match(uri);
switch (match) {
case CONTACTS: {
invalidateFastScrollingIndexCache();
return 0;
}
case CONTACTS_ID: {
invalidateFastScrollingIndexCache();
long contactId = ContentUris.parseId(uri);
return deleteContact(contactId, callerIsSyncAdapter);
}
default: {
mSyncToNetwork = true;
return mLegacyApiSupport.delete(uri, selection, selectionArgs);
}
}
}
private int deleteContact(long contactId, boolean callerIsSyncAdapter) {
//得到SQLiteOpenHelper
final SQLiteDatabase db = mDbHelper.get().getWritableDatabase();
mSelectionArgs1[0] = Long.toString(contactId);
//先查询相关信息
Cursor c = db.query(Tables.RAW_CONTACTS, new String[]{RawContacts._ID}, RawContacts.CONTACT_ID + "=?", mSelectionArgs1, null, null, null);
try {
while (c.moveToNext()) {
long rawContactId = c.getLong(0);
markRawContactAsDeleted(db, rawContactId, callerIsSyncAdapter);
}
} finally {
c.close();
}
mProviderStatusUpdateNeeded = true;
//删除SQLite
return db.delete(Tables.CONTACTS, Contacts._ID + "=" + contactId, null);
}
我们详细看一下SQLiteDatabase的delete()过程：
@SQLiteDatabase.java
public int delete(String table, String whereClause, String[] whereArgs) {
acquireReference();
try {
//构建SQL语句
SQLiteStatement statement = new SQLiteStatement(this, "DELETE FROM " + table + (!TextUtils.isEmpty(whereClause) ? " WHERE " + whereClause : ""), whereArgs);
try {
//执行删除命令
return statement.executeUpdateDelete();
} finally {
statement.close();
}
} finally {
releaseReference();
}
}
到这里，我们终于完成了从ContentProvider到SQLite的“历程”。
5.3、ProfileProvider的操作
首先要切换数据库为ProfileDatabaseHelper： private void switchToProfileMode() {
//为mDbHelper设置ProfileDatabaseHelper
mDbHelper.set(mProfileHelper);
mTransactionContext.set(mProfileTransactionContext);
mAggregator.set(mProfileAggregator);
mPhotoStore.set(mProfilePhotoStore);
mInProfileMode.set(true);
}
mProfileProvider.delete(uri, selection, selectionArgs);
@AbstractContactsProvider.java
public int delete(Uri uri, String selection, String[] selectionArgs) {
ContactsTransaction transaction = startTransaction(false);
try {
//把delete转换为事务的处理方式
int deleted = deleteInTransaction(uri, selection, selectionArgs);
if (deleted > 0) {
transaction.markDirty();
}
transaction.markSuccessful(false);
return deleted;
} finally {
endTransaction(false);
}
}
protected abstract int deleteInTransaction(Uri uri, String selection, String[] selectionArgs);
@ProfileProvider.java
protected int deleteInTransaction(Uri uri, String selection, String[] selectionArgs) {
enforceWritePermission();
useProfileDbForTransaction();
return mDelegate.deleteInTransaction(uri, selection, selectionArgs);
}
这里的mDelegate就是ContactsProvider2本身，因此在ProfileProvider中扰了一圈，又回到了ContactsProvider2中的deleteInTransaction()，而这个方法我们在5.2节已经介绍过详细的流程。
六、总结
现在我们回顾一下整个流程：
1、当我们调用getContentResolver().delete()后，将会通过getContentResolver()得到ContentResolver对象，然后调用该对象的delete()方法。
2、在ContentResolver中，会通过acquireProvider()的方法得到IContentProvider对象，而这个对象的获取首先需要ActivityThread中向ActivityManagerService申请的ContentProvider的详细信息（ContentProviderHolder），然后利用这个Holder去得到（getIContentProvider）ContentProvider的远程代理对象（Transport对象）。
3、拿到这个对象之后，调用其delete方法，该方法将会由ContentProvider传递给其子类（AbstractContactsProvider），并在子类中将delete操作转换为事务处理的方式（deleteInTransaction），AbstractContactsProvider中虽然将处理方式转换成事务的方式，但是却没有具体的实现，而是把具体的操作留给其子类（ContactsProvider2）完成。
4、ContactsProvider2在实现过程中将会用相应的SQLiteOpenHelper去把操作转换成具体的SQLite语句并执行。
下面我们用一张图来结束本次的学习。
