介绍
ContentProvider作为四大组件之一，它可以为其他组件或者其他应用提供数据。它会在进程启动时同时启动并发布到AMS中，现在通过源码来学习了解相关流程。
//BookProvider 继承自ContentProvider
Uri uri = Uri.parse("content://com.m1ku.testproject.provider.BookProvider");
getContentResolver().query(uri, null, null, null, null);
源码分析
从query方法作为入口切入源码
首先通过getContentResolver()获取ContentResolver对象
@Override
public ContentResolver getContentResolver() {
return mBase.getContentResolver();
}
调用ContextImpl的方法
@Override
public ContentResolver getContentResolver() {
return mContentResolver;
}
ContentResolver是一个抽象类，这里返回它的实现ApplicationContentResolver对象，该对象在ContextImpl构造时初始化。
调用ContentResolver的query方法
public final @Nullable Cursor query(@RequiresPermission.Read @NonNull Uri uri,
@Nullable String[] projection, @Nullable String selection,
@Nullable String[] selectionArgs, @Nullable String sortOrder) {
return query(uri, projection, selection, selectionArgs, sortOrder, null);
}
public final @Nullable Cursor query(@RequiresPermission.Read @NonNull Uri uri,
@Nullable String[] projection, @Nullable String selection,
@Nullable String[] selectionArgs, @Nullable String sortOrder,
@Nullable CancellationSignal cancellationSignal) {
Bundle queryArgs = createSqlQueryBundle(selection, selectionArgs, sortOrder);
return query(uri, projection, queryArgs, cancellationSignal);
}
public final @Nullable Cursor query(final @RequiresPermission.Read @NonNull Uri uri,
@Nullable String[] projection, @Nullable Bundle queryArgs,
@Nullable CancellationSignal cancellationSignal) {
//...
IContentProvider unstableProvider = acquireUnstableProvider(uri);
//...
}
调用ApplicationContentResolver的acquireUnstableProvider
@Override
protected IContentProvider acquireUnstableProvider(Context c, String auth) {
return mMainThread.acquireProvider(c,
ContentProvider.getAuthorityWithoutUserId(auth),
resolveUserIdFromAuthority(auth), false);
}
调用ActivityThread的acquireProvider
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;
}
ContentProviderHolder holder = null;
try {
holder = ActivityManager.getService().getContentProvider(
getApplicationThread(), auth, userId, stable);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
holder = installProvider(c, holder, holder.info,
true /*noisy*/, holder.noReleaseNeeded, stable);
return holder.provider;
}
首先会查询该ContentProvider是否存在，如果存在的话直接将其返回。否则远程调用AMS的getContentProvider方法
@Override
public final ContentProviderHolder getContentProvider(
IApplicationThread caller, String name, int userId, boolean stable) {
//...
return getContentProviderImpl(caller, name, null, stable, userId);
}
private ContentProviderHolder getContentProviderImpl(IApplicationThread caller,
String name, IBinder token, boolean stable, int userId) {
//...
ProcessRecord proc = getProcessRecordLocked(
cpi.processName, cpr.appInfo.uid, false);
if (proc != null && proc.thread != null && !proc.killed) {
if (!proc.pubProviders.containsKey(cpi.name)) {
proc.pubProviders.put(cpi.name, cpr);
try {
proc.thread.scheduleInstallProvider(cpi);
} catch (RemoteException e) {
}
}
} else {
proc = startProcessLocked(cpi.processName,
cpr.appInfo, false, 0, "content provider",
new ComponentName(cpi.applicationInfo.packageName,
cpi.name), false, false, false);
}
cpr.launchingApp = proc;
mLaunchingProviders.add(cpr);
//...
}
如果ContentProvider所在的进程还未启动的话，会调用startProcessLocked启动该进程，该方法的调用栈中最终会调用Process.start方法启动进程，新进程启动后入口方法就是ActivityThread的main方法
public static void main(String[] args) {
Looper.prepareMainLooper();
ActivityThread thread = new ActivityThread();
thread.attach(false);
if (sMainThreadHandler == null) {
sMainThreadHandler = thread.getHandler();
}
Looper.loop();
}
在main方法中，首先初始化了ActivityThread对象，并调用其attach方法，最后开启了主线程的消息循环。
private void attach(boolean system) {
//...
final IActivityManager mgr = ActivityManager.getService();
try {
mgr.attachApplication(mAppThread);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
//...
}
attach方法中远程调用AMS的attachApplication方法将ApplicationThread传入到AMS中
@Override
public final void attachApplication(IApplicationThread thread) {
synchronized (this) {
//...
attachApplicationLocked(thread, callingPid);
//...
}
}
private final boolean attachApplicationLocked(IApplicationThread thread,
int pid) {
//...
thread.bindApplication(processName, appInfo, providers,
app.instr.mClass,
profilerInfo, app.instr.mArguments,
app.instr.mWatcher,
app.instr.mUiAutomationConnection, testMode,
mBinderTransactionTrackingEnabled, enableTrackAllocation,
isRestrictedBackupMode || !normalMode, app.persistent,
new Configuration(getGlobalConfiguration()), app.compat,
getCommonServicesLocked(app.isolated),
mCoreSettingsObserver.getCoreSettingsLocked(),
buildSerial);
//...
}
调用ApplicationThread的bindApplication方法，在该方法中发送了一个H.BIND_APPLICATION类型的消息，该消息的处理方法为
private void handleBindApplication(AppBindData data) {
//...
final ContextImpl appContext = ContextImpl.createAppContext(this, data.info);
//...
final ClassLoader cl = instrContext.getClassLoader();
mInstrumentation = (Instrumentation)
cl.loadClass(data.instrumentationName.getClassName()).newInstance();
//...
Application app = data.info.makeApplication(data.restrictedBackupMode, null);
mInitialApplication = app;
//...
if (!data.restrictedBackupMode) {
if (!ArrayUtils.isEmpty(data.providers)) {
installContentProviders(app, data.providers);
mH.sendEmptyMessageDelayed(H.ENABLE_JIT, 10*1000);
}
}
//...
mInstrumentation.callApplicationOnCreate(app);
}
首先创建了ContextImpl对象，然后用类加载器创建了Instrumentation对象，调用makeApplication
public Application makeApplication(boolean forceDefaultAppClass,
Instrumentation instrumentation) {
//...
ContextImpl appContext = ContextImpl.createAppContext(mActivityThread, this);
app = mActivityThread.mInstrumentation.newApplication(
cl, appClass, appContext);
appContext.setOuterContext(app);
//...
}
调用newApplication完成了Application对象的创建。在完成Application的创建后，会调用installContentProviders初始化该进程中的ContentProvider
private void installContentProviders(
Context context, List providers) {
final ArrayList results = new ArrayList<>();
for (ProviderInfo cpi : providers) {
if (DEBUG_PROVIDER) {
StringBuilder buf = new StringBuilder(128);
buf.append("Pub ");
buf.append(cpi.authority);
buf.append(": ");
buf.append(cpi.name);
Log.i(TAG, buf.toString());
}
ContentProviderHolder cph = installProvider(context, null, cpi,
false /*noisy*/, true /*noReleaseNeeded*/, true /*stable*/);
if (cph != null) {
cph.noReleaseNeeded = true;
results.add(cph);
}
}
try {
ActivityManager.getService().publishContentProviders(
getApplicationThread(), results);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
}
遍历providers，调用installProvider方法
private ContentProviderHolder installProvider(Context context,
ContentProviderHolder holder, ProviderInfo info,
boolean noisy, boolean noReleaseNeeded, boolean stable) {
//...
final java.lang.ClassLoader cl = c.getClassLoader();
localProvider = (ContentProvider)cl.loadClass(info.name).newInstance();
//...
localProvider.attachInfo(c, info);
}
这里通过类加载器构建了ContentProvider对象，然后调用attachInfo方法，其中回调了ContentProvider的onCreate方法，由于该方法是由主线程mH Handler执行的，所以onCreate回调在主线程中。最后远程调用AMS的publishContentProviders方法将他们保存在AMS中。ContentProvider完成创建后，在handleBindApplication中又回调了Application的onCreate方法，所以这里ContentProvider的onCreate是先于Application的onCreate方法调用的。
调用query方法查询时，我们通过acquireUnstableProvider获得的是IContentProvider这个Binder接口，而它的实现是ContentProviderNative和ContentProvider.Transport，Transport对象继承自ContentProviderNative，那么这里就是调用的Transport的query方法。这里是通过Binder来调用的，外界无法访问直接访问ContentProvider，它只能通过AMS根据Uri来获取对应的ContentProvider的Binder接口，再通过IContentProvider来访问ContentProvider中的数据源。
@Override
public Cursor query(String callingPkg, Uri uri, @Nullable String[] projection,
@Nullable Bundle queryArgs, @Nullable ICancellationSignal cancellationSignal) {
//...
Cursor cursor = ContentProvider.this.query(
uri, projection, queryArgs,
CancellationSignal.fromTransport(cancellationSignal));
//...
}
最后就调用到了ContentProvider的query方法，这个query方法执行在Binder线程中，方法的执行结果会通过Binder返回给调用者。这里以query方法为例分析了ContentProvider的工作流程，而其他几个方法也是类似的。