Step 10. ActivityManagerService.systemReady
这个函数是在上面的Step 6中的ServerThread.run函数在将系统中的一系列服务都初始化完毕之后才调用的，它定义在frameworks/base/services/java/com/android/server/am/ActivityManagerServcie.java文件中：
- public final class ActivityManagerService extends ActivityManagerNative
- implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
- ......
- public void systemReady(final Runnable goingCallback) {
- ......
- synchronized (this) {
- ......
- mMainStack.resumeTopActivityLocked(null);
- }
- }
- ......
- }
这个函数的内容比较多，这里省去无关的部分，主要关心启动Home应用程序的逻辑，这里就是通过mMainStack.resumeTopActivityLocked函数来启动Home应用程序的了，这里的mMainStack是一个ActivityStack类型的实例变量
Step 11. ActivityStack.resumeTopActivityLocked
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 resumeTopActivityLocked(ActivityRecord prev) {
- // Find the first activity that is not finishing.
- ActivityRecord next = topRunningActivityLocked(null);
- ......
- if (next == null) {
- // There are no more activities! Let's just start up the
- // Launcher...
- if (mMainStack) {
- return mService.startHomeActivityLocked();
- }
- }
- ......
- }
- ......
- }
这里调用函数topRunningActivityLocked返回的是当前系统Activity堆栈最顶端的Activity，由于此时还没有Activity被启动过，因此，返回值为null，即next变量的值为null，于是就调用mService.startHomeActivityLocked语句，这里的mService就是前面在Step 7中创建的ActivityManagerService实例了。
Step 12. ActivityManagerService.startHomeActivityLocked
这个函数定义在frameworks/base/services/java/com/android/server/am/ActivityManagerServcie.java文件中：
- public final class ActivityManagerService extends ActivityManagerNative
- implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
- ......
- boolean startHomeActivityLocked() {
- ......
- Intent intent = new Intent(
- mTopAction,
- mTopData != null ? Uri.parse(mTopData) : null);
- intent.setComponent(mTopComponent);
- if (mFactoryTest != SystemServer.FACTORY_TEST_LOW_LEVEL) {
- intent.addCategory(Intent.CATEGORY_HOME);
- }
- ActivityInfo aInfo =
- intent.resolveActivityInfo(mContext.getPackageManager(),
- STOCK_PM_FLAGS);
- if (aInfo != null) {
- intent.setComponent(new ComponentName(
- aInfo.applicationInfo.packageName, aInfo.name));
- // Don't do this if the home app is currently being
- // instrumented.
- ProcessRecord app = getProcessRecordLocked(aInfo.processName,
- aInfo.applicationInfo.uid);
- if (app == null || app.instrumentationClass == null) {
- intent.setFlags(intent.getFlags() | Intent.FLAG_ACTIVITY_NEW_TASK);
- mMainStack.startActivityLocked(null, intent, null, null, 0, aInfo,
- null, null, 0, 0, 0, false, false);
- }
- }
- return true;
- }
- ......
- }
函数首先创建一个CATEGORY_HOME类型的Intent，然后通过Intent.resolveActivityInfo函数向PackageManagerService查询Category类型为HOME的Activity，这里我们假设只有系统自带的Launcher应用程序注册了HOME类型的Activity（见packages/apps/Launcher2/AndroidManifest.xml文件）
- <manifest
- xmlns:android="http://schemas.android.com/apk/res/android"
- package="com.android.launcher"
- android:sharedUserId="@string/sharedUserId"
- >
- ......
- <application
- android:name="com.android.launcher2.LauncherApplication"
- android:process="@string/process"
- android:label="@string/application_name"
- android:icon="@drawable/ic_launcher_home">
- <activity
- android:name="com.android.launcher2.Launcher"
- android:launchMode="singleTask"
- android:clearTaskOnLaunch="true"
- android:stateNotNeeded="true"
- android:theme="@style/Theme"
- android:screenOrientation="nosensor"
- android:windowSoftInputMode="stateUnspecified|adjustPan">
- <intent-filter>
- <action android:name="android.intent.action.MAIN" />
- <category android:name="android.intent.category.HOME" />
- <category android:name="android.intent.category.DEFAULT" />
- <category android:name="android.intent.category.MONKEY"/>
- </intent-filter>
- </activity>
- ......
- </application>
- </manifest>
因此，这里就返回com.android.launcher2.Launcher这个Activity了。由于是第一次启动这个Activity，接下来调用函数getProcessRecordLocked返回来的ProcessRecord值为null，于是，就调用mMainStack.startActivityLocked函数启动com.android.launcher2.Launcher这个Activity了，这里的mMainStack是一个ActivityStack类型的成员变量。
