续前节，我们已经知道，Zygote孵化完进程之后会invoke ActivityThread#main方法，现在继续看剩下的部分。该方法代码如下：
/frameworks/base/core/java/android/app/ActivityThread.java
public static void main(String[] args) {
...
Looper.prepareMainLooper();
ActivityThread thread = new ActivityThread();
thread.attach(false);
if (sMainThreadHandler == null) {
sMainThreadHandler = thread.getHandler();
}
...
Looper.loop();
throw new RuntimeException("Main thread loop unexpectedly exited");
}
可以看到这里首先开启了Looper消息循环，这部分知识我们以后再来分析。下面主要看下ActivityThread#attach(boolean)方法，代码如下：
private void attach(boolean system) {
sCurrentActivityThread = this;
mSystemThread = system;
if (!system) {
...
RuntimeInit.setApplicationObject(mAppThread.asBinder());
final IActivityManager mgr = ActivityManagerNative.getDefault();
try {
mgr.attachApplication(mAppThread);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
...
} else {
...
}
...
}
因为不是系统APP，所以只需要看if里的代码就好了。之前已经分析过，ActivityManagerNative#getDefault()方法获取到的是ActivityManagerProxy实例，然后这个实例通过BinderProxy与ActivityManagerService进行通信。接下来代码如下：
/frameworks/base/core/java/android/app/ActivityManagerNative.java
public void attachApplication(IApplicationThread app) throws RemoteException
{
Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IActivityManager.descriptor);
data.writeStrongBinder(app.asBinder());
mRemote.transact(ATTACH_APPLICATION_TRANSACTION, data, reply, 0);
reply.readException();
data.recycle();
reply.recycle();
}
和之前的做法非常一致，接下来会执行到ActivityManagerService#onTransact方法，而相关代码在父类ActivityManagerNative中，代码如下：
case ATTACH_APPLICATION_TRANSACTION: {
data.enforceInterface(IActivityManager.descriptor);
IApplicationThread app = ApplicationThreadNative.asInterface(
data.readStrongBinder());
if (app != null) {
attachApplication(app);
}
reply.writeNoException();
return true;
}
这里看到IApplicationThread实例是通过ApplicationThreadNative#asInterface获取的，根据先前的经验，这里应该是一个ApplicationThreadProxy实例，相关代码如下：
/frameworks/base/core/java/android/app/ApplicationThreadNative.java
static public IApplicationThread asInterface(IBinder obj) {
if (obj == null) {
return null;
}
IApplicationThread in =
(IApplicationThread)obj.queryLocalInterface(descriptor);
if (in != null) {
return in;
}
return new ApplicationThreadProxy(obj);
}
接下来就可以确认，ActivityManagerService#attachApplication(IApplicationThread)方法中的IApplicationThread实例是ApplicationThreadProxy，代码如下：
/frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
public final void attachApplication(IApplicationThread thread) {
synchronized (this) {
int callingPid = Binder.getCallingPid();
final long origId = Binder.clearCallingIdentity();
attachApplicationLocked(thread, callingPid);
Binder.restoreCallingIdentity(origId);
}
}
private final boolean attachApplicationLocked(IApplicationThread thread,
int pid) {
...
try {
...
thread.bindApplication(processName, appInfo, providers, app.instrumentationClass,
profilerInfo, app.instrumentationArguments, app.instrumentationWatcher,
app.instrumentationUiAutomationConnection, testMode,
mBinderTransactionTrackingEnabled, enableTrackAllocation,
isRestrictedBackupMode || !normalMode, app.persistent,
new Configuration(mConfiguration), app.compat,
getCommonServicesLocked(app.isolated),
mCoreSettingsObserver.getCoreSettingsLocked());
updateLruProcessLocked(app, false, null);
app.lastRequestedGc = app.lastLowMemory = SystemClock.uptimeMillis();
} catch (Exception e) {
...
}
...
// See if the top visible activity is waiting to run in this process...
if (normalMode) {
try {
if (mStackSupervisor.attachApplicationLocked(app)) {
didSomething = true;
}
} catch (Exception e) {
Slog.wtf(TAG, "Exception thrown launching activities in " + app, e);
badApp = true;
}
}
...
return true;
}
然后看下这里ApplicationThreadProxy#bindApplication方法，代码如下：
/frameworks/base/core/java/android/app/ApplicationThreadNative.java
public final void bindApplication(String packageName, ApplicationInfo info,
List<ProviderInfo> providers, ComponentName testName, ProfilerInfo profilerInfo,
Bundle testArgs, IInstrumentationWatcher testWatcher,
IUiAutomationConnection uiAutomationConnection, int debugMode,
boolean enableBinderTracking, boolean trackAllocation, boolean restrictedBackupMode,
boolean persistent, Configuration config, CompatibilityInfo compatInfo,
Map<String, IBinder> services, Bundle coreSettings) throws RemoteException {
...
mRemote.transact(BIND_APPLICATION_TRANSACTION, data, null,
IBinder.FLAG_ONEWAY);
data.recycle();
}
这里的思路和ActivityManagerNative十分一致，通过ApplicationThreadProxy与BinderProxy来完成ApplicationThread与ActivityManagerService通信，然后由ApplicationThreadNative处理返回的结果，并调用ApplicationThread的对应方法。接下来看下ApplicationThread#bindApplication方法：
/frameworks/base/core/java/android/app/ActivityThread.java
public final void bindApplication(String processName, ApplicationInfo appInfo,
List<ProviderInfo> providers, ComponentName instrumentationName,
ProfilerInfo profilerInfo, Bundle instrumentationArgs,
IInstrumentationWatcher instrumentationWatcher,
IUiAutomationConnection instrumentationUiConnection, int debugMode,
boolean enableBinderTracking, boolean trackAllocation,
boolean isRestrictedBackupMode, boolean persistent, Configuration config,
CompatibilityInfo compatInfo, Map<String, IBinder> services, Bundle coreSettings) {
if (services != null) {
// Setup the service cache in the ServiceManager
ServiceManager.initServiceCache(services);
}
setCoreSettings(coreSettings);
AppBindData data = new AppBindData();
data.processName = processName;
data.appInfo = appInfo;
data.providers = providers;
data.instrumentationName = instrumentationName;
data.instrumentationArgs = instrumentationArgs;
data.instrumentationWatcher = instrumentationWatcher;
data.instrumentationUiAutomationConnection = instrumentationUiConnection;
data.debugMode = debugMode;
data.enableBinderTracking = enableBinderTracking;
data.trackAllocation = trackAllocation;
data.restrictedBackupMode = isRestrictedBackupMode;
data.persistent = persistent;
data.config = config;
data.compatInfo = compatInfo;
data.initProfilerInfo = profilerInfo;
sendMessage(H.BIND_APPLICATION, data);
}
这里把一些需要设置的属性，通过一个叫AppBindData的方式包装起来，然后通过Handler方式，发送给了一个叫H的Handler实例，这个实例在ActivityThread中，我们看下它在handleMessage中对BIND_APPLICATION这个消息的处理：
case BIND_APPLICATION:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "bindApplication");
AppBindData data = (AppBindData)msg.obj;
handleBindApplication(data);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
private void handleBindApplication(AppBindData data) {
...
// Continue loading instrumentation.
if (ii != null) {
...
mInstrumentation.init(this, instrContext, appContext, component,
data.instrumentationWatcher, data.instrumentationUiAutomationConnection);
if (mProfiler.profileFile != null && !ii.handleProfiling
&& mProfiler.profileFd == null) {
mProfiler.handlingProfiling = true;
final File file = new File(mProfiler.profileFile);
file.getParentFile().mkdirs();
Debug.startMethodTracing(file.toString(), 8 * 1024 * 1024);
}
} else {
mInstrumentation = new Instrumentation();
}
...
try {
// If the app is being launched for full backup or restore, bring it up in
// a restricted environment with the base application class.
Application app = data.info.makeApplication(data.restrictedBackupMode, null);
mInitialApplication = app;
...
// Do this after providers, since instrumentation tests generally start their
// test thread at this point, and we don't want that racing.
try {
mInstrumentation.onCreate(data.instrumentationArgs);
}
catch (Exception e) {
...
}
try {
mInstrumentation.callApplicationOnCreate(app);
} catch (Exception e) {
...
}
} finally {
StrictMode.setThreadPolicy(savedPolicy);
}
}
handleBindApplication做了非常多的工作，APP的名称、资源、屏幕相关等操作都在这里进行了处理，但这不是我们今天关注的重点，我们主要看最下边的try-catch，这里首先创建了一个Application实例，然后调用了mInstrumentation.onCreate和mInstrumentation.callApplicationOnCreate，这两个方法一个是空的，一个调用了Application#onCreate()，没有做更多的事情，这里暂时不关注它。这里这个Application实例是通过LoadedApk#makeApplication完成的，代码如下：
/frameworks/base/core/java/android/app/LoadedApk.java
public Application makeApplication(boolean forceDefaultAppClass,
Instrumentation instrumentation) {
if (mApplication != null) {
return mApplication;
}
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "makeApplication");
Application app = null;
String appClass = mApplicationInfo.className;
if (forceDefaultAppClass || (appClass == null)) {
appClass = "android.app.Application";
}
try {
java.lang.ClassLoader cl = getClassLoader();
if (!mPackageName.equals("android")) {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER,
"initializeJavaContextClassLoader");
initializeJavaContextClassLoader();
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
}
ContextImpl appContext = ContextImpl.createAppContext(mActivityThread, this);
app = mActivityThread.mInstrumentation.newApplication(
cl, appClass, appContext);
appContext.setOuterContext(app);
} catch (Exception e) {
...
}
mActivityThread.mAllApplications.add(app);
mApplication = app;
if (instrumentation != null) {
try {
instrumentation.callApplicationOnCreate(app);
} catch (Exception e) {
...
}
}
...
return app;
}
可以看到这个Application是通过Instrumentation#newApplication方法完成的，代码如下：
/frameworks/base/core/java/android/app/Instrumentation.java
public Application newApplication(ClassLoader cl, String className, Context context)
throws InstantiationException, IllegalAccessException,
ClassNotFoundException {
return newApplication(cl.loadClass(className), context);
}
static public Application newApplication(Class<?> clazz, Context context)
throws InstantiationException, IllegalAccessException,
ClassNotFoundException {
Application app = (Application)clazz.newInstance();
app.attach(context);
return app;
}
这里看到Application是通过ClassLoader创建出来的，随后调用了它的attach方法，该方法如下：
/frameworks/base/core/java/android/app/Application.java
/* package */ final void attach(Context context) {
attachBaseContext(context);
mLoadedApk = ContextImpl.getImpl(context).mPackageInfo;
}
至此，Application就创建完毕了，并且Application#onCreate()方法也执行完毕了。接下来就是启动Activity的过程，在之前分析ActivityManagerService#attachApplicationLocked方法中，执行完毕thread.bindApplication之后又执行了mStackSupervisor.attachApplicationLocked(app)，也就是创建完Application之后，启动需要运行的Activity，相应的代码如下：
/frameworks/base/services/core/java/com/android/server/am/ActivityStackSupervisor.java
boolean attachApplicationLocked(ProcessRecord app) throws RemoteException {
final String processName = app.processName;
boolean didSomething = false;
for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {
ArrayList<ActivityStack> stacks = mActivityDisplays.valueAt(displayNdx).mStacks;
for (int stackNdx = stacks.size() - 1; stackNdx >= 0; --stackNdx) {
final ActivityStack stack = stacks.get(stackNdx);
if (!isFocusedStack(stack)) {
continue;
}
ActivityRecord hr = stack.topRunningActivityLocked();
if (hr != null) {
if (hr.app == null && app.uid == hr.info.applicationInfo.uid
&& processName.equals(hr.processName)) {
try {
if (realStartActivityLocked(hr, app, true, true)) {
didSomething = true;
}
} catch (RemoteException e) {
Slog.w(TAG, "Exception in new application when starting activity "
+ hr.intent.getComponent().flattenToShortString(), e);
throw e;
}
}
}
}
}
if (!didSomething) {
ensureActivitiesVisibleLocked(null, 0, !PRESERVE_WINDOWS);
}
return didSomething;
}
因为是首次运行，所以会执行到if (realStartActivityLocked(hr, app, true, true))代码块，如下所示：
final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app,
boolean andResume, boolean checkConfig) throws RemoteException {
...
final ActivityStack stack = task.stack;
try {
...
app.forceProcessStateUpTo(mService.mTopProcessState);
app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken,
System.identityHashCode(r), r.info, new Configuration(mService.mConfiguration),
new Configuration(task.mOverrideConfig), r.compat, r.launchedFromPackage,
task.voiceInteractor, app.repProcState, r.icicle, r.persistentState, results,
newIntents, !andResume, mService.isNextTransitionForward(), profilerInfo);
...
} catch (RemoteException e) {
...
}
...
return true;
}
现在，终于开始加载Activity了，代码如下：
/frameworks/base/core/java/android/app/ActivityThread.java
public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
ActivityInfo info, Configuration curConfig, Configuration overrideConfig,
CompatibilityInfo compatInfo, String referrer, IVoiceInteractor voiceInteractor,
int procState, Bundle state, PersistableBundle persistentState,
List<ResultInfo> pendingResults, List<ReferrerIntent> pendingNewIntents,
boolean notResumed, boolean isForward, ProfilerInfo profilerInfo) {
updateProcessState(procState, false);
ActivityClientRecord r = new ActivityClientRecord();
...
sendMessage(H.LAUNCH_ACTIVITY, r);
}
可以看到这里依然是通过H来交互的，代码如下：
case LAUNCH_ACTIVITY: {
...
handleLaunchActivity(r, null, "LAUNCH_ACTIVITY");
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
} break;
private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent, String reason) {
...
Activity a = performLaunchActivity(r, customIntent);
if (a != null) {
r.createdConfig = new Configuration(mConfiguration);
reportSizeConfigurations(r);
Bundle oldState = r.state;
handleResumeActivity(r.token, false, r.isForward,
!r.activity.mFinished && !r.startsNotResumed, r.lastProcessedSeq, reason);
...
} else {
...
}
}
这里首先通过performLaunchActivity获取到需要加载的Activity，然后调用handleResumeActivity方法。我们先看前者，代码如下：
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
...
Activity activity = null;
try {
java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
...
} catch (Exception e) {
...
}
try {
Application app = r.packageInfo.makeApplication(false, mInstrumentation);
...
if (activity != null) {
Context appContext = createBaseContextForActivity(r, activity);
...
activity.attach(appContext, this, getInstrumentation(), r.token,
r.ident, app, r.intent, r.activityInfo, title, r.parent,
r.embeddedID, r.lastNonConfigurationInstances, config,
r.referrer, r.voiceInteractor, window);
...
if (theme != 0) {
activity.setTheme(theme);
}
activity.mCalled = false;
if (r.isPersistable()) {
mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
} else {
mInstrumentation.callActivityOnCreate(activity, r.state);
}
...
if (!r.activity.mFinished) {
activity.performStart();
r.stopped = false;
}
if (!r.activity.mFinished) {
if (r.isPersistable()) {
if (r.state != null || r.persistentState != null) {
mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state,
r.persistentState);
}
} else if (r.state != null) {
mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state);
}
}
if (!r.activity.mFinished) {
activity.mCalled = false;
if (r.isPersistable()) {
mInstrumentation.callActivityOnPostCreate(activity, r.state,
r.persistentState);
} else {
mInstrumentation.callActivityOnPostCreate(activity, r.state);
}
...
}
}
r.paused = true;
mActivities.put(r.token, r);
} catch (SuperNotCalledException e) {
throw e;
} catch (Exception e) {
...
}
return activity;
}
这里首先通过Instrumentation#newActivity方法创建了一个Activity，然后调用了它的一些生命周期方法，包括它的Theme、Window等都是在这时候设置的，还是先看下创建的过程，代码如下：
public Activity newActivity(ClassLoader cl, String className,
Intent intent)
throws InstantiationException, IllegalAccessException,
ClassNotFoundException {
return (Activity)cl.loadClass(className).newInstance();
}
和创建Application一样，也是通过ClassLoader完成的，Activity创建完成后接着调用了Activity#attach方法，在最开始时候提到过这个方法，并说它需要的ActivityThread是通过这个方法传入的，这里终于找到调用的地方了。接下来依次调用了Activity的onCreate、onStart、onRestoreInstanceState和onPostCreate方法，最后回到handleLaunchActivity，调用了handleResumeActivity。接下来的代码就涉及到了Activity加载View了，我们之后再分析。
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