Android应用程序启动过程源代码分析（4）
Step 28. ActivityStack.realStartActivityLocked
这个函数定义在frameworks/base/services/java/com/android/server/am/ActivityStack.java文件中：
- public class ActivityStack {
- ......
- final boolean realStartActivityLocked(ActivityRecord r,
- ProcessRecord app, boolean andResume, boolean checkConfig)
- throws RemoteException {
- ......
- r.app = app;
- ......
- int idx = app.activities.indexOf(r);
- if (idx < 0) {
- app.activities.add(r);
- }
- ......
- try {
- ......
- List<ResultInfo> results = null;
- List<Intent> newIntents = null;
- if (andResume) {
- results = r.results;
- newIntents = r.newIntents;
- }
- ......
- app.thread.scheduleLaunchActivity(new Intent(r.intent), r,
- System.identityHashCode(r),
- r.info, r.icicle, results, newIntents, !andResume,
- mService.isNextTransitionForward());
- ......
- } catch (RemoteException e) {
- ......
- }
- ......
- return true;
- }
- ......
- }
这里最终通过app.thread进入到ApplicationThreadProxy的scheduleLaunchActivity函数中，注意，这里的第二个参数r，是一个ActivityRecord类型的Binder对象，用来作来这个Activity的token值。
Step 29. ApplicationThreadProxy.scheduleLaunchActivity
这个函数定义在frameworks/base/core/java/android/app/ApplicationThreadNative.java文件中：
- class ApplicationThreadProxy implements IApplicationThread {
- ......
- public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
- ActivityInfo info, Bundle state, List<ResultInfo> pendingResults,
- List<Intent> pendingNewIntents, boolean notResumed, boolean isForward)
- throws RemoteException {
- Parcel data = Parcel.obtain();
- data.writeInterfaceToken(IApplicationThread.descriptor);
- intent.writeToParcel(data, 0);
- data.writeStrongBinder(token);
- data.writeInt(ident);
- info.writeToParcel(data, 0);
- data.writeBundle(state);
- data.writeTypedList(pendingResults);
- data.writeTypedList(pendingNewIntents);
- data.writeInt(notResumed ? 1 : 0);
- data.writeInt(isForward ? 1 : 0);
- mRemote.transact(SCHEDULE_LAUNCH_ACTIVITY_TRANSACTION, data, null,
- IBinder.FLAG_ONEWAY);
- data.recycle();
- }
- ......
- }
这个函数最终通过Binder驱动程序进入到ApplicationThread的scheduleLaunchActivity函数中。
Step 30. ApplicationThread.scheduleLaunchActivity
这个函数定义在frameworks/base/core/java/android/app/ActivityThread.java文件中：
- public final class ActivityThread {
- ......
- private final class ApplicationThread extends ApplicationThreadNative {
- ......
- // we use token to identify this activity without having to send the
- // activity itself back to the activity manager. (matters more with ipc)
- public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
- ActivityInfo info, Bundle state, List<ResultInfo> pendingResults,
- List<Intent> pendingNewIntents, boolean notResumed, boolean isForward) {
- ActivityClientRecord r = new ActivityClientRecord();
- r.token = token;
- r.ident = ident;
- r.intent = intent;
- r.activityInfo = info;
- r.state = state;
- r.pendingResults = pendingResults;
- r.pendingIntents = pendingNewIntents;
- r.startsNotResumed = notResumed;
- r.isForward = isForward;
- queueOrSendMessage(H.LAUNCH_ACTIVITY, r);
- }
- ......
- }
- ......
- }
函数首先创建一个ActivityClientRecord实例，并且初始化它的成员变量，然后调用ActivityThread类的queueOrSendMessage函数进一步处理。
Step 31. ActivityThread.queueOrSendMessage
这个函数定义在frameworks/base/core/java/android/app/ActivityThread.java文件中：
- public final class ActivityThread {
- ......
- private final class ApplicationThread extends ApplicationThreadNative {
- ......
- // if the thread hasn't started yet, we don't have the handler, so just
- // save the messages until we're ready.
- private final void queueOrSendMessage(int what, Object obj) {
- queueOrSendMessage(what, obj, 0, 0);
- }
- ......
- private final void queueOrSendMessage(int what, Object obj, int arg1, int arg2) {
- synchronized (this) {
- ......
- Message msg = Message.obtain();
- msg.what = what;
- msg.obj = obj;
- msg.arg1 = arg1;
- msg.arg2 = arg2;
- mH.sendMessage(msg);
- }
- }
- ......
- }
- ......
- }
函数把消息内容放在msg中，然后通过mH把消息分发出去，这里的成员变量mH我们在前面已经见过，消息分发出去后，最后会调用H类的handleMessage函数。
Step 32. H.handleMessage
这个函数定义在frameworks/base/core/java/android/app/ActivityThread.java文件中：
- public final class ActivityThread {
- ......
- private final class H extends Handler {
- ......
- public void handleMessage(Message msg) {
- ......
- switch (msg.what) {
- case LAUNCH_ACTIVITY: {
- ActivityClientRecord r = (ActivityClientRecord)msg.obj;
- r.packageInfo = getPackageInfoNoCheck(
- r.activityInfo.applicationInfo);
- handleLaunchActivity(r, null);
- } break;
- ......
- }
- ......
- }
- ......
- }
这里最后调用ActivityThread类的handleLaunchActivity函数进一步处理。
Step 33. ActivityThread.handleLaunchActivity
这个函数定义在frameworks/base/core/java/android/app/ActivityThread.java文件中：
- public final class ActivityThread {
- ......
- private final void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) {
- ......
- Activity a = performLaunchActivity(r, customIntent);
- if (a != null) {
- r.createdConfig = new Configuration(mConfiguration);
- Bundle oldState = r.state;
- handleResumeActivity(r.token, false, r.isForward);
- ......
- } else {
- ......
- }
- }
- ......
- }
这里首先调用performLaunchActivity函数来加载这个Activity类，即shy.luo.activity.MainActivity，然后调用它的onCreate函数，最后回到handleLaunchActivity函数时，再调用handleResumeActivity函数来使这个Activity进入Resumed状态，即会调用这个Activity的onResume函数，这是遵循Activity的生命周期的。
Step 34. ActivityThread.performLaunchActivity
这个函数定义在frameworks/base/core/java/android/app/ActivityThread.java文件中：
- public final class ActivityThread {
- ......
- private final Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
- ActivityInfo aInfo = r.activityInfo;
- if (r.packageInfo == null) {
- r.packageInfo = getPackageInfo(aInfo.applicationInfo,
- 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();
- activity = mInstrumentation.newActivity(
- cl, component.getClassName(), r.intent);
- r.intent.setExtrasClassLoader(cl);
- if (r.state != null) {
- r.state.setClassLoader(cl);
- }
- } catch (Exception e) {
- ......
- }
- try {
- Application app = r.packageInfo.makeApplication(false, mInstrumentation);
- ......
- if (activity != null) {
- ContextImpl appContext = new ContextImpl();
- appContext.init(r.packageInfo, r.token, this);
- appContext.setOuterContext(activity);
- CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager());
- Configuration config = new Configuration(mConfiguration);
- ......
- activity.attach(appContext, this, getInstrumentation(), r.token,
- r.ident, app, r.intent, r.activityInfo, title, r.parent,
- r.embeddedID, r.lastNonConfigurationInstance,
- r.lastNonConfigurationChildInstances, config);
- if (customIntent != null) {
- activity.mIntent = customIntent;
- }
- r.lastNonConfigurationInstance = null;
- r.lastNonConfigurationChildInstances = null;
- activity.mStartedActivity = false;
- int theme = r.activityInfo.getThemeResource();
- if (theme != 0) {
- activity.setTheme(theme);
- }
- activity.mCalled = false;
- mInstrumentation.callActivityOnCreate(activity, r.state);
- ......
- r.activity = activity;
- r.stopped = true;
- if (!r.activity.mFinished) {
- activity.performStart();
- r.stopped = false;
- }
- if (!r.activity.mFinished) {
- if (r.state != null) {
- mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state);
- }
- }
- if (!r.activity.mFinished) {
- activity.mCalled = false;
- 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) {
- ......
- } catch (Exception e) {
- ......
- }
- return activity;
- }
- ......
- }
函数前面是收集要启动的Activity的相关信息，主要package和component信息：
- ActivityInfo aInfo = r.activityInfo;
- if (r.packageInfo == null) {
- r.packageInfo = getPackageInfo(aInfo.applicationInfo,
- 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);
- }
然后通过ClassLoader将shy.luo.activity.MainActivity类加载进来：
- Activity activity = null;
- try {
- java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
- activity = mInstrumentation.newActivity(
- cl, component.getClassName(), r.intent);
- r.intent.setExtrasClassLoader(cl);
- if (r.state != null) {
- r.state.setClassLoader(cl);
- }
- } catch (Exception e) {
- ......
- }
接下来是创建Application对象，这是根据AndroidManifest.xml配置文件中的Application标签的信息来创建的：
- Application app = r.packageInfo.makeApplication(false, mInstrumentation);
后面的代码主要创建Activity的上下文信息，并通过attach方法将这些上下文信息设置到MainActivity中去：
- activity.attach(appContext, this, getInstrumentation(), r.token,
- r.ident, app, r.intent, r.activityInfo, title, r.parent,
- r.embeddedID, r.lastNonConfigurationInstance,
- r.lastNonConfigurationChildInstances, config);
最后还要调用MainActivity的onCreate函数：
- mInstrumentation.callActivityOnCreate(activity, r.state);
这里不是直接调用MainActivity的onCreate函数，而是通过mInstrumentation的callActivityOnCreate函数来间接调用，前面我们说过，mInstrumentation在这里的作用是监控Activity与系统的交互操作，相当于是系统运行日志。