getContentResolver().delete();
这个简单的操作其实包含了两个步骤:
下面我们就开启此次漫长的旅程。
为了解答这两个问题,我们需要从代码的最源头开始分析:
@ContextImpl.java
public ContentResolver getContentResolver() {
return mContentResolver;
}
这里的mContentResolver是在ContextImpl的init中完成初始化的:
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;
}
mContentResolver被初始化为ApplicationContentResolver对象,我们再来看ApplicationContentResolver这个类,他是ContextImpl的内部类:
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) { }
}
他提供了得到IContentProvider的各种方法,而且继承自ContentResolver类,我们来看这个类的属性:
@ContentResolver.java
public abstract class ContentResolver { }
可以看到,ContentResolver并没有继承任何的类或者接口,因此,我们可以认为,
从继承关系上来讲,ContentResolver与ContentProvider没有任何关系。
那么我们是如何最终得到ContentProvider的呢?
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){}
这就说明,两者在功能上一定有联系,下面我们从最开始的delete操作去分析,看两者究竟有什么关系。
@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 {
}
}
在这一步中,我们先通过acquireProvider()得到IContentProvider对象,然后调用IContentProvider对象的delete方法进行操作。那么,这里是如何通过acquireProvider()得到IContentProvider对象的呢?
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;
}
继续看:
protected abstract IContentProvider acquireProvider(Context c, String name);
这里竟然遇到了抽象的acquireProvider,说明这个方法需要到子类中实现,那么我们就去ApplicationContentResolver中去看看:
@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);
}
}
我们确实在ApplicationContentResolver中找到了acquireProvider()方法,而且发现
acquireProvider方法所提供的返回值是来自于mMainThread对象的acquireProvider方法。
接下来所介绍的流程,比较复杂,各位看好了。
@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);
}
此时将会调用ContextImpl中的init方法:
@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);
}
这个过程我们发现,
mMainThread就是ActivityThread对象,因此在2.2中我们介绍的mMainThread.acquireProvider()相当于:
ActivityThread.acquireProvider();
我们继续看:
@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;
}
这里可以看到,
ActivityThread中存在一个HashMap用来缓存所有的provider。每一次对provider的请求,都会先通过acquireExistingProvider()查询是否已经被缓存,如果没有缓存,就去创建该provider的ContentProviderHolder对象,同时缓存下来方便下次调用。
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。
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。
@SystemServer.java
public void run() {
//启动ActivityManagerService
context = ActivityManagerService.main(factoryTest);
//注册ActivityManagerService
ActivityManagerService.setSystemProcess();
}
上面调用ActivityManagerService.main方法的结果就是启动ActivityManagerService,然后调用setSystemProcess把ActivityManagerService注册给系统:
@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) {
}
}
我们再来看ActivityManagerService的继承关系:
public final class ActivityManagerService extends ActivityManagerNative implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {}
说明这个Server继承自ActivityManagerNative,而且父类主要完成一些Binder的操作。
@ActivityManagerNative.java
static public IActivityManager getDefault() {
return gDefault.get();
}
我们看,调用ActivityManagerNative的getDefault()方法的结果就是得到gDefault对象里面的数据,那么gDefault里面究竟放着怎样的数据呢?我们来看他的定义:
private static final Singleton gDefault = new Singleton() {
protected IActivityManager create() {
IBinder b = ServiceManager.getService("activity");
IActivityManager am = asInterface(b);
return am;
}
};
原来,在gDefault变量的初始化过程中(create),完成了两步重要的操作:
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);
}
通过asInterface()的细节我们发现,
我们得到的远程代理对象就是ActivityManagerProxy对象。也就是说我们当初的:
ActivityManagerNative.getDefault().getContentProvider( getApplicationThread(), auth, userId, stable);
其实相当于:
ActivityManagerProxy.getContentProvider(getApplicationThread(), auth, userId, stable);;
现在我们已经弄明白了2.4中提到的第一步操作,下面我们来分析第二部操作。
@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;
}
}
我们看到,在getContentProvider的过程中,ActivityManagerProxy把请求通过mRemote发送给远端的ActivityManagerNative去处理,请求码为GET_CONTENT_PROVIDER_TRANSACTION。
@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;
}
}
}
}
在onTransact中把该请求又发送给了真正的服务端ActivityManagerService.getContentProvider():
@ActivityManagerService.java
public final ContentProviderHolder getContentProvider( IApplicationThread caller, String name, int userId, boolean stable) {
return getContentProviderImpl(caller, name, null, stable, userId);
}
继续看服务端的操作:
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;
}
在上面这个过程中,我们发现,
在ActivityManagerService中有存在着一个mProviderMap的变量用于保存当前系统中所有的provider,其中每一项都是一个ContentProviderRecord型的数据,通过这个数据可以完成两个重要作用:
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;
}
在前面的过程中,我们通过ActivityManagerService得到了ContentProviderHolder对象,该对象是对provider的详细描述,
下面我们需要用这些描述在installProvider()方法中开启provider,并获得该provider的代理对象。
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;
}
我们清晰的看到,在installProvider的方法中,我们
用ActivityManagerService中得到的ContentProvider信息,去加载该ContentProvider(localProvider),并调用他的getIContentProvider()方法得到该provider的代理对象。
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。
@ContentProvider.java
public IContentProvider getIContentProvider() {
return mTransport;
}
这里得到的只是IContentProvider类型的mTransport变量,而这个变量的来历呢?
private Transport mTransport = new Transport();
这就说明,通过getIContentProvider()的方法得到的只是Transport对象,他是ContentProvider的内部类:
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) { }
}
而且我们发现这个内部类提供了用于查询数据库的各项操作。那么当我们进行delete操作的时候呢?
public int delete(Uri uri, String selection, String[] selectionArgs) {
enforceWritePermission(uri);
return ContentProvider.this.delete(uri, selection, selectionArgs);
}
既然Transport内部把delete操作传递给了ContentProvider去操作,那么我们就来看看ContentProvider本身对delete()的处理:
public abstract int delete(Uri uri, String selection, String[] selectionArgs);
这里我们遇到了抽象的方法,也就是说,delete操作的具体细节需要在ContentProvider的子类中实现了,这也符合ContentProvider框架的设计理念,即:
ContentProvider负责抽象部分的表述,具体的操作需要各自private自己去实现。
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 { }
}
从ContentProvider提供的方法我们发现,除了权限管理类的方法外,其他的就是一些与delete类似的、与数据库处理相关的抽象方法。
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
@AndroidManifest.xml
这段声明告诉系统该provider的name、authorities、permission等信息,简单来说,这个数据库的名字叫做ContactsProvider2,可以通过contacts或者com.android.contacts的前缀来匹配,而且访问这个数据库需要相应的权限READ_CONTACTS、WRITE_CONTACTS等。
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();
}
从注释中可以看出,他主要提供与事务处理相关的回调方法,其中onBegin是事务开始处理之后时调用的回调函数,onCommit是事务提交之后的回调函数,onRollback是事务回滚时的回调函数,由此推断,
在ContactsProvider中使用了事务的方式对数据库进行操作。
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();
}
这些方法都很好理解,均是对数据库的各项操作。还记得我们在分析ContentProvider的delete操作时提到,ContentProvider把对数据库的各项操作放到子类中处理,对当前环境来说,就是需要在AbstractContactsProvider中处理的,因此delete的操作就应该调用的这里:
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);
}
}
继续看deleteInTransaction的实现:
protected abstract int deleteInTransaction(Uri uri, String selection, String[] selectionArgs);
这仍然是个虚函数,具体定义需要留给子类去实现。
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() { }
}
我们从ProfileProvider的结构看出,他具备独立的query操作,以及插入、删除、更新的事务操作,以及事务相关的回调函数,可以说,他具备了完整的数据访问、修改能力。但是他的作用呢?
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。
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 {}
继承关系如下:
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;
}
我们先看ContactsDatabaseHelper初始化过程:
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;
}
再来看ProfileDatabaseHelper初始化过程:
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;
}
因为在ContactsProvider中存在两个“不同”的SQLiteOpenHelper,因此在具体的数据库操作时,需要根据不同需要来切换(switchToXXXMode)不同的SQLiteOpenHelper去操作。切换的过程我们稍后再讲。
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。
@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);
}
}
在delete的过程中,根据mapsToProfileDb()的判断,需要切换两种模式:Profile与Contact模式,这也是我们刚刚讲的,需要根据不同的情况切换不同的SQLiteOpenHelper去操作数据库,我们现在来看一下区分两种模式的依据:
private boolean mapsToProfileDb(Uri uri) {
return sUriMatcher.mapsToProfile(uri);
}
这里是根据给出的uri去sUriMatcher中查找是否有匹配的项,如果有,就认为需要转换到Profile模式去处理,那么sUriMatcher中究竟有哪些项呢?
@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);
//......
}
我们发现,在ContactsContract中定义的URI都在这个MAP中,也就是说,我们用ContactsContract中的URI去操作数据库时,都应该满足mapsToProfileDb的条件。
下面我们分别看这两种情况具体的操作。
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);
}
这里最重要的操作就是将mDbHelper中内容置换为mContactsHelper,也就是ContactsDatabaseHelper。接下来就是super.delete()的操作,这里的super对ContactsProvider2来说就是AbstractContactsProvider:
@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);
这个“转换”的操作我们之前分析过,就是把delete操作转换为事务处理的方式,具体操作需要在子类中实现,因此又回到了ContactsProvider2中的deleteInTransaction:
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);
}
}
}
这里我们假设匹配的是CONTACTS_ID:
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);
}
在deleteContact的过程中,要先得到可用的SQLiteDatabase,当前来说就是得到ContactsDatabaseHelper的SQLiteDatabase,然后查询数据库得到Cursor,并遍历每一项标记其删除的标记,最后再调用SQLiteDatabase的delete()方法将该条记录删除。
@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();
}
}
我们看到,delete操作中,先
通过SQLiteStatement生成SQL语句(DELETE FROM XXX WHERE XXX),然后通过executeUpdateDelete()方法去应用该SQL操作,从而完成delete的操作。
到这里,我们终于完成了从ContentProvider到SQLite的“历程”。
private void switchToProfileMode() {
//为mDbHelper设置ProfileDatabaseHelper
mDbHelper.set(mProfileHelper);
mTransactionContext.set(mProfileTransactionContext);
mAggregator.set(mProfileAggregator);
mPhotoStore.set(mProfilePhotoStore);
mInProfileMode.set(true);
}
然后进行删除动作:
mProfileProvider.delete(uri, selection, selectionArgs);
也就是调用ProfileProvider中的delete方法,但是在ProfileProvider没有找到delete方法,我们只能去其父类AbstractContactsProvider中调用delete():
@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);
经过AbstractContactsProvider的“转换”,将delete操作转换到子类中的deleteInTransaction():
@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。
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。