Android系统默认Home应用程序（Launcher）的启动过程源代码分析（2）

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：

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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：

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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：

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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）

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<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。