从应用启动看Activity的创建过程

本篇暂未完成。

/*

*Acitivity的创建过程：

*应用程序的入口为ActivityThread的main函数。

*在main函数中：

*/

public static void main(String[] args) {

SamplingProfilerIntegration.start();

// CloseGuard defaults to true and can be quite spammy.  We
// disable it here, but selectively enable it later (via
// StrictMode) on debug builds, but using DropBox, not logs.
CloseGuard.setEnabled(false);

//为当前的User初始化一个用户目录，以及一些环境变量
Environment.initForCurrentUser();

// Set the reporter for event logging in libcore
EventLogger.setReporter(new EventLoggingReporter());

Security.addProvider(new AndroidKeyStoreProvider());

// Make sure TrustedCertificateStore looks in the right place for CA certificates
final File configDir = Environment.getUserConfigDirectory(UserHandle.myUserId());
TrustedCertificateStore.setDefaultUserDirectory(configDir);

Process.setArgV0("<pre-initialized>");

Looper.prepareMainLooper();

//创建了一个AcitivityThread，
ActivityThread thread = new ActivityThread();
thread.attach(false);

if (sMainThreadHandler == null) {
sMainThreadHandler = thread.getHandler();
}

AsyncTask.init();

if (false) {
Looper.myLooper().setMessageLogging(new
LogPrinter(Log.DEBUG, "ActivityThread"));
}

Looper.loop();

throw new RuntimeException("Main thread loop unexpectedly exited");
}

private void attach(boolean system) {
//将当前的ActivityThread对象赋值给ActivityThread的静态变量sCurrentActivityThread
sCurrentActivityThread = this;
mSystemThread = system;//system=false
if (!system) {
ViewRootImpl.addFirstDrawHandler(new Runnable() {
@Override
public void run() {
ensureJitEnabled();
}
});
android.ddm.DdmHandleAppName.setAppName("<pre-initialized>",
UserHandle.myUserId());
RuntimeInit.setApplicationObject(mAppThread.asBinder());
//ActivityManagerNative属于IPC代理类，IPC服务端是ActivityManagerService
final IActivityManager mgr = ActivityManagerNative.getDefault();
try {
/*IPC调用attachApplication，aAppThread是ApplicationThread类型。
ApplicationThread继承于ApplicationThreadNative，ApplicationThreadNative继承于Binder。
Application创建之前的一些工作
*/
mgr.attachApplication(mAppThread);
} catch (RemoteException ex) {
// Ignore
}
// Watch for getting close to heap limit.
BinderInternal.addGcWatcher(new Runnable() {
@Override public void run() {
if (!mSomeActivitiesChanged) {
return;
}
Runtime runtime = Runtime.getRuntime();
long dalvikMax = runtime.maxMemory();
long dalvikUsed = runtime.totalMemory() - runtime.freeMemory();
if (dalvikUsed > ((3*dalvikMax)/4)) {
if (DEBUG_MEMORY_TRIM) Slog.d(TAG, "Dalvik max=" + (dalvikMax/1024)
+ " total=" + (runtime.totalMemory()/1024)
+ " used=" + (dalvikUsed/1024));
mSomeActivitiesChanged = false;
try {
mgr.releaseSomeActivities(mAppThread);
} catch (RemoteException e) {
}
}
}
});
} else {
//由于system为false，所以此处不执行

android.ddm.DdmHandleAppName.setAppName("system_process",
UserHandle.myUserId());
try {
//接下来是创建ContextImpl，Application，调用Application的onCreate
mInstrumentation = new Instrumentation();
ContextImpl context = ContextImpl.createAppContext(
this, getSystemContext().mPackageInfo);
mInitialApplication = context.mPackageInfo.makeApplication(true, null);
mInitialApplication.onCreate();
} catch (Exception e) {
throw new RuntimeException(
"Unable to instantiate Application():" + e.toString(), e);
}
}

// add dropbox
4000
logging to libcore
DropBox.setReporter(new DropBoxReporter());

ViewRootImpl.addConfigCallback(new ComponentCallbacks2() {
@Override
public void onConfigurationChanged(Configuration newConfig) {
synchronized (mResourcesManager) {
// We need to apply this change to the resources
// immediately, because upon returning the view
// hierarchy will be informed about it.
if (mResourcesManager.applyConfigurationToResourcesLocked(newConfig, null)) {
// This actually changed the resources!  Tell
// everyone about it.
if (mPendingConfiguration == null ||
mPendingConfiguration.isOtherSeqNewer(newConfig)) {
mPendingConfiguration = newConfig;

sendMessage(H.CONFIGURATION_CHANGED, newConfig);
}
}
}
}
@Override
public void onLowMemory() {
}
@Override
public void onTrimMemory(int level) {
}
});
}

//在ActivityManagerService.java中：
@Override
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) {

// Find the application record that is being attached...  either via
// the pid if we are running in multiple processes, or just pull the
// next app record if we are emulating process with anonymous threads.
ProcessRecord app;
if (pid != MY_PID && pid >= 0) {
synchronized (mPidsSelfLocked) {
app = mPidsSelfLocked.get(pid);
}
} else {
app = null;
}

if (app == null) {
Slog.w(TAG, "No pending application record for pid " + pid
+ " (IApplicationThread " + thread + "); dropping process");
EventLog.writeEvent(EventLogTags.AM_DROP_PROCESS, pid);
if (pid > 0 && pid != MY_PID) {
Process.killProcessQuiet(pid);
//TODO: Process.killProcessGroup(app.info.uid, pid);
} else {
try {
thread.scheduleExit();
} catch (Exception e) {
// Ignore exceptions.
}
}
return false;
}

//此处省去部分代码
......

boolean badApp = false;
boolean didSomething = false;

// 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;
}
}

//此处省去部分代码
......

return true;
}

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 (!isFrontStack(stack)) {
continue;
}
ActivityRecord hr = stack.topRunningActivityLocked(null);
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);
}
return didSomething;
}

final boolean realStartActivityLocked(ActivityRecord r,
ProcessRecord app, boolean andResume, boolean checkConfig)
throws RemoteException {

r.startFreezingScreenLocked(app, 0);
if (false) Slog.d(TAG, "realStartActivity: setting app visibility true");
mWindowManager.setAppVisibility(r.appToken, true);

......

//在此处通过IPC方式调用了ActivityThread的scheduleLaunchActivity，
//scheduleLaunchActivity方法向主线程消息队列中发送了一个LAUNCH_ACTIVITY的消息。
app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken,
System.identityHashCode(r), r.info, new Configuration(mService.mConfiguration),
r.compat, r.task.voiceInteractor, app.repProcState, r.icicle, r.persistentState,
results, newIntents, !andResume, mService.isNextTransitionForward(),
profilerInfo);
//此处省去部分代码
......
return true;
}

//到此在ActivityThread.java.attch()中的mgr.attachApplication(mAppThread);这句代码就执行完了。
//attach方法执行完后，ActivityThread的Handler就去执行LAUNCH_ACTIVITY的消息了。也就是执行handleLaunchActivity().

private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) {
// If we are getting ready to gc after going to the background, well
// we are back active so skip it.
unscheduleGcIdler();
mSomeActivitiesChanged = true;
//此处省去部分代码
......

//此处终于创建了Acitivity
Activity a = performLaunchActivity(r, customIntent);

if (a != null) {
r.createdConfig = new Configuration(mConfiguration);
Bundle oldState = r.state;
handleResumeActivity(r.token, false, r.isForward,
!r.activity.mFinished && !r.startsNotResumed);
//此处省去部分代码
.....

} else {
// If there was an error, for any reason, tell the activity
// manager to stop us.
try {
ActivityManagerNative.getDefault()
.finishActivity(r.token, Activity.RESULT_CANCELED, null, false);
} catch (RemoteException ex) {
// Ignore
}
}
}

//这里有两个重要的方法。
//1.performLaunchActivity。
//2.handleResumeActivity

private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
// System.out.println("##### [" + System.currentTimeMillis() + "] ActivityThread.performLaunchActivity(" + r + ")");

ActivityInfo aInfo = r.activityInfo;
if (r.packageInfo == null) {
r.packageInfo = getPackageInfo(aInfo.applicationInfo, r.compatInfo,
Context.CONTEXT_INCLUDE_CODE);
}

ComponentName component = r.intent.getComponent();
if (component == null) {
component = r.intent.resolveActivity(
mInitialApplication.getPackageManager());
r.intent.setComponent(component);
}

if (r.activityInfo.targetActivity != null) {
component = new ComponentName(r.activityInfo.packageName,
r.activityInfo.targetActivity);
}

Activity activity = null;
try {
java.lang.ClassLoader cl = r.packageInfo.getClassLoader();

//此处创建了Activity对象
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
StrictMode.incrementExpectedActivityCount(activity.getClass());
r.intent.setExtrasClassLoader(cl);
r.intent.prepareToEnterProcess();
if (r.state != null) {
r.state.setClassLoader(cl);
}
} catch (Exception e) {
if (!mInstrumentation.onException(activity, e)) {
throw new RuntimeException(
"Unable to instantiate activity " + component
+ ": " + e.toString(), e);
}
}

try {
//创建Application对象
Application app = r.packageInfo.makeApplication(false, mInstrumentation);

if (activity != null) {
Context appContext = createBaseContextForActivity(r, activity);
CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager());
Configuration config = new Configuration(mCompatConfiguration);

activity.attach(appContext, this, getInstrumentation(), r.token,
r.ident, app, r.intent, r.activityInfo, title, r.parent,
r.embeddedID, r.lastNonConfigurationInstances, config,
r.voiceInteractor);

if (customIntent != null) {
activity.mIntent = customI
ea4b
ntent;
}
r.lastNonConfigurationInstances = null;
activity.mStartedActivity = false;

//在此设置activity的主题
int theme = r.activityInfo.getThemeResource();
if (theme != 0) {
activity.setTheme(theme);
}

activity.mCalled = false;
//调用Activity的onCreate方法
if (r.isPersistable()) {
mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
} else {
mInstrumentation.callActivityOnCreate(activity, r.state);
}
if (!activity.mCalled) {
throw new SuperNotCalledException(
"Activity " + r.intent.getComponent().toShortString() +
" did not call through to super.onCreate()");
}
r.activity = activity;
r.stopped = true;
//调用activity的onStart方法
if (!r.activity.mFinished) {
activity.performStart();
r.stopped = false;
}
//调用activity的OnRestoreInstanceState方法
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);
}
}
//调用activity的onPostCreate方法
if (!r.activity.mFinished) {
activity.mCalled = false;
if (r.isPersistable()) {
mInstrumentation.callActivityOnPostCreate(activity, r.state,
r.persistentState);
} else {
mInstrumentation.callActivityOnPostCreate(activity, r.state);
}
if (!activity.mCalled) {
throw new SuperNotCalledException(
"Activity " + r.intent.getComponent().toShortString() +
" did not call through to super.onPostCreate()");
}
}
}
r.paused = true;

mActivities.put(r.token, r);

} catch (SuperNotCalledException e) {
throw e;

} catch (Exception e) {
if (!mInstrumentation.onException(activity, e)) {
throw new RuntimeException(
"Unable to start activity " + component
+ ": " + e.toString(), e);
}
}

return activity;
}

//调用了mInstrumentation.newActivity去创建Activity。
//之后，调用了Activity的attach方法，在其中创建了window，设置了windowManager，
public Activity newActivity(ClassLoader cl, String className,
Intent intent)
throws InstantiationException, IllegalAccessException,
ClassNotFoundException {
return (Activity)cl.loadClass(className).newInstance();
}
//newActivity方法很简单，通过反射创建Activity。

//看完了performLaunchActivity。就进入另一个重要的方法handleResumeActivity
final void handleResumeActivity(IBinder token,
boolean clearHide, boolean isForward, boolean reallyResume) {
// If we are getting ready to gc after going to the background, well
// we are back active so skip it.
unscheduleGcIdler();
mSomeActivitiesChanged = true;

// TODO Push resumeArgs into the activity for consideration
ActivityClientRecord r = performResumeActivity(token, clearHide);

if (r != null) {
final Activity a = r.activity;

if (localLOGV) Slog.v(
TAG, "Resume " + r + " started activity: " +
a.mStartedActivity + ", hideForNow: " + r.hideForNow
+ ", finished: " + a.mFinished);

final int forwardBit = isForward ?
WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION : 0;

// If the window hasn't yet been added to the window manager,
// and this guy didn't finish itself or start another activity,
// then go ahead and add the window.
boolean willBeVisible = !a.mStartedActivity;
if (!willBeVisible) {
try {
willBeVisible = ActivityManagerNative.getDefault().willActivityBeVisible(
a.getActivityToken());
} catch (RemoteException e) {
}
}
if (r.window == null && !a.mFinished && willBeVisible) {
r.window = r.activity.getWindow();
View decor = r.window.getDecorView();
decor.setVisibility(View.INVISIBLE);
ViewManager wm = a.getWindowManager();
WindowManager.LayoutParams l = r.window.getAttributes();
a.mDecor = decor;
l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
l.softInputMode |= forwardBit;
if (a.mVisibleFromClient) {
a.mWindowAdded = true;
wm.addView(decor, l);
}

// If the window has already been added, but during resume
// we started another activity, then don't yet make the
// window visible.
} else if (!willBeVisible) {
if (localLOGV) Slog.v(
TAG, "Launch " + r + " mStartedActivity set");
r.hideForNow = true;
}

// Get rid of anything left hanging around.
cleanUpPendingRemoveWindows(r);

// The window is now visible if it has been added, we are not
// simply finishing, and we are not starting another activity.
if (!r.activity.mFinished && willBeVisible
&& r.activity.mDecor != null && !r.hideForNow) {
if (r.newConfig != null) {
if (DEBUG_CONFIGURATION) Slog.v(TAG, "Resuming activity "
+ r.activityInfo.name + " with newConfig " + r.newConfig);
performConfigurationChanged(r.activity, r.newConfig);
freeTextLayoutCachesIfNeeded(r.activity.mCurrentConfig.diff(r.newConfig));
r.newConfig = null;
}
if (localLOGV) Slog.v(TAG, "Resuming " + r + " with isForward="
+ isForward);
WindowManager.LayoutParams l = r.window.getAttributes();
if ((l.softInputMode
& WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION)
!= forwardBit) {
l.softInputMode = (l.softInputMode
& (~WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION))
| forwardBit;
if (r.activity.mVisibleFromClient) {
ViewManager wm = a.getWindowManager();
View decor = r.window.getDecorView();
wm.updateViewLayout(decor, l);
}
}
r.activity.mVisibleFromServer = true;
mNumVisibleActivities++;
if (r.activity.mVisibleFromClient) {
r.activity.makeVisible();
}
}

if (!r.onlyLocalRequest) {
r.nextIdle = mNewActivities;
mNewActivities = r;
if (localLOGV) Slog.v(
TAG, "Scheduling idle handler for " + r);
Looper.myQueue().addIdleHandler(new Idler());
}
r.onlyLocalRequest = false;

// Tell the activity manager we have resumed.
if (reallyResume) {
try {
ActivityManagerNative.getDefault().activityResumed(token);
} catch (RemoteException ex) {
}
}

} else {
// If an exception was thrown when trying to resume, then
// just end this activity.
try {
ActivityManagerNative.getDefault()
.finishActivity(token, Activity.RESULT_CANCELED, null, false);
} catch (RemoteException ex) {
}
}
}

//先看看performResumeActivity方法。在此方法中调用activity的生命周期函数onResume。
public final ActivityClientRecord performResumeActivity(IBinder token,
boolean clearHide) {
ActivityClientRecord r = mActivities.get(token);
if (localLOGV) Slog.v(TAG, "Performing resume of " + r
+ " finished=" + r.activity.mFinished);
if (r != null && !r.activity.mFinished) {
if (clearHide) {
r.hideForNow = false;
r.activity.mStartedActivity = false;
}
try {
r.activity.mFragments.noteStateNotSaved();
if (r.pendingIntents != null) {
deliverNewIntents(r, r.pendingIntents);
r.pendingIntents = null;
}
if (r.pendingResults != null) {
deliverResults(r, r.pendingResults);
r.pendingResults = null;
}

//调用onResume方法
r.activity.performResume();

EventLog.writeEvent(LOG_ON_RESUME_CALLED,
UserHandle.myUserId(), r.activity.getComponentName().getClassName());

r.paused = false;
r.stopped = false;
r.state = null;
r.persistentState = null;
} catch (Exception e) {
if (!mInstrumentation.onException(r.activity, e)) {
throw new RuntimeException(
"Unable to resume activity "
+ r.intent.getComponent().toShortString()
+ ": " + e.toString(), e);
}
}
}
return r;
}

//然后重点就是下面这段代码：
if (r.window == null && !a.mFinished && willBeVisible) {
//先拿到window和windowManager对象，这两个对象在上面介绍的Activity的attch方法中创建。
r.window = r.activity.getWindow();
View decor = r.window.getDecorView();
decor.setVisibility(View.INVISIBLE);
ViewManager wm = a.getWindowManager();
WindowManager.LayoutParams l = r.window.getAttributes();
a.mDecor = decor;
l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
l.softInputMode |= forwardBit;
if (a.mVisibleFromClient) {
a.mWindowAdded = true;
//windowManager显示decorView，此方法
wm.addView(decor, l);
}

// If the window has already been added, but during resume
// we started another activity, then don't yet make the
// window visible.
} else if (!willBeVisible) {
if (localLOGV) Slog.v(
TAG, "Launch " + r + " mStartedActivity set");
r.hideForNow = true;
}

做个备注：

在ActivityThread.java中：

H是Handler的字类。负责处理Activity的各种操作。

performLaunchActivity中创建了Activity

LoadApk中存储了ActivityThread的引用，还有其他的一些关于该应用的目录等变量。

CompatibilityInfo类保存了应用程序运行的兼容性模式的信息

我们平时在Activity中使用的ContentResolver是ApplicationContentResolver类型的