介紹
ContentProvider作為四大組件之一，它可以為其他組件或者其他應(yīng)用提供數(shù)據(jù)。它會在進(jìn)程啟動時同時啟動并發(fā)布到AMS中，現(xiàn)在通過源碼來學(xué)習(xí)了解相關(guān)流程。
//BookProvider 繼承自ContentProvider
Uri uri = Uri.parse("content://com.m1ku.testproject.provider.BookProvider");
getContentResolver().query(uri, null, null, null, null);
源碼分析
從query方法作為入口切入源碼
首先通過getContentResolver()獲取ContentResolver對象
@Override
public ContentResolver getContentResolver() {
return mBase.getContentResolver();
}
調(diào)用ContextImpl的方法
@Override
public ContentResolver getContentResolver() {
return mContentResolver;
}
ContentResolver是一個抽象類，這里返回它的實現(xiàn)ApplicationContentResolver對象，該對象在ContextImpl構(gòu)造時初始化。
調(diào)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);
//...
}
調(diào)用ApplicationContentResolver的acquireUnstableProvider
@Override
protected IContentProvider acquireUnstableProvider(Context c, String auth) {
return mMainThread.acquireProvider(c,
ContentProvider.getAuthorityWithoutUserId(auth),
resolveUserIdFromAuthority(auth), false);
}
調(diào)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;
}
首先會查詢該ContentProvider是否存在，如果存在的話直接將其返回。否則遠(yuǎn)程調(diào)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所在的進(jìn)程還未啟動的話，會調(diào)用startProcessLocked啟動該進(jìn)程，該方法的調(diào)用棧中最終會調(diào)用Process.start方法啟動進(jìn)程，新進(jìn)程啟動后入口方法就是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對象，并調(diào)用其attach方法，最后開啟了主線程的消息循環(huán)。
private void attach(boolean system) {
//...
final IActivityManager mgr = ActivityManager.getService();
try {
mgr.attachApplication(mAppThread);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
//...
}
attach方法中遠(yuǎn)程調(diào)用AMS的attachApplication方法將ApplicationThread傳入到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);
//...
}
調(diào)用ApplicationThread的bindApplication方法，在該方法中發(fā)送了一個H.BIND_APPLICATION類型的消息，該消息的處理方法為
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);
}
首先創(chuàng)建了ContextImpl對象，然后用類加載器創(chuàng)建了Instrumentation對象，調(diào)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);
//...
}
調(diào)用newApplication完成了Application對象的創(chuàng)建。在完成Application的創(chuàng)建后，會調(diào)用installContentProviders初始化該進(jìn)程中的ContentProvider
private void installContentProviders(
Context context, List<ProviderInfo> providers) {
final ArrayList<ContentProviderHolder> 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();
}
}
遍歷providers，調(diào)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);
}
這里通過類加載器構(gòu)建了ContentProvider對象，然后調(diào)用attachInfo方法，其中回調(diào)了ContentProvider的onCreate方法，由于該方法是由主線程mH Handler執(zhí)行的，所以onCreate回調(diào)在主線程中。最后遠(yuǎn)程調(diào)用AMS的publishContentProviders方法將他們保存在AMS中。ContentProvider完成創(chuàng)建后，在handleBindApplication中又回調(diào)了Application的onCreate方法，所以這里ContentProvider的onCreate是先于Application的onCreate方法調(diào)用的。
調(diào)用query方法查詢時，我們通過acquireUnstableProvider獲得的是IContentProvider這個Binder接口，而它的實現(xiàn)是ContentProviderNative和ContentProvider.Transport，Transport對象繼承自ContentProviderNative，那么這里就是調(diào)用的Transport的query方法。這里是通過Binder來調(diào)用的，外界無法訪問直接訪問ContentProvider，它只能通過AMS根據(jù)Uri來獲取對應(yīng)的ContentProvider的Binder接口，再通過IContentProvider來訪問ContentProvider中的數(shù)據(jù)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));
//...
}
最后就調(diào)用到了ContentProvider的query方法，這個query方法執(zhí)行在Binder線程中，方法的執(zhí)行結(jié)果會通過Binder返回給調(diào)用者。這里以query方法為例分析了ContentProvider的工作流程，而其他幾個方法也是類似的。
