Android 设置向导启动分析

一、Android 系统启动流程

Bootloader 系统引导
启动 Linux 内核
启动 init 进程
启动 Zygote 进程
启动 SystemServer 进程
- 启动 Binder 线程池
- 创建 SystemServiceManager 并启动各种 SystemService

二、启动设置向导或 Launcher

SystemServer 会在 startBootstrapServices() 方法中会启动 ActivityManagerService 。

private void startBootstrapServices() {...// Activity manager runs the show.mActivityManagerService = mSystemServiceManager.startService(ActivityManagerService.Lifecycle.class).getService();...
}
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在 startOtherServices() 方法中会调用 ActivityManagerService 的 systemReday() 方法。

private void startOtherServices() {
...mActivityManagerService.systemReady(new Runnable() {@Overridepublic void run() {Slog.i(TAG, "Making services ready");mSystemServiceManager.startBootPhase(SystemService.PHASE_ACTIVITY_MANAGER_READY);...}
...
}
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ActivityManagerService 的 systemReday() 方法中会调用 startHomeActivityLocked() 方法。

public void systemReady(final Runnable goingCallback) {...synchronized (this) {...startHomeActivityLocked(currentUserId, "systemReady");...}...
}
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startHomeActivityLocked() 方法中会获取到 Action 为 Intent.ACTION_MAIN，Category 为 Intent.CATEGORY_HOME 的 Intent，根据该 Intent 获取到符合条件的应用，并判断该应用是否已经启动，没有启动则启动该应用。

...
String mTopAction = Intent.ACTION_MAIN;
...
// 获取 Action 为 Intent.ACTION_MAIN，Category 为 Intent.CATEGORY_HOME 的 Intent
Intent getHomeIntent() {Intent intent = new Intent(mTopAction, mTopData != null ? Uri.parse(mTopData) : null);intent.setComponent(mTopComponent);intent.addFlags(Intent.FLAG_DEBUG_TRIAGED_MISSING);if (mFactoryTest != FactoryTest.FACTORY_TEST_LOW_LEVEL) {intent.addCategory(Intent.CATEGORY_HOME);}return intent;
}boolean startHomeActivityLocked(int userId, String reason) {if (mFactoryTest == FactoryTest.FACTORY_TEST_LOW_LEVEL&& mTopAction == null) {// We are running in factory test mode, but unable to find// the factory test app, so just sit around displaying the// error message and don't try to start anything.return false;}Intent intent = getHomeIntent();// 获取符合条件的应用ActivityInfo aInfo = resolveActivityInfo(intent, STOCK_PM_FLAGS, userId);if (aInfo != null) {intent.setComponent(new ComponentName(aInfo.applicationInfo.packageName, aInfo.name));// Don't do this if the home app is currently being// instrumented.aInfo = new ActivityInfo(aInfo);aInfo.applicationInfo = getAppInfoForUser(aInfo.applicationInfo, userId);ProcessRecord app = getProcessRecordLocked(aInfo.processName,aInfo.applicationInfo.uid, true);// 判断应用是否启动，未启动则启动该应用程序if (app == null || app.instrumentationClass == null) {intent.setFlags(intent.getFlags() | Intent.FLAG_ACTIVITY_NEW_TASK);// 启动应用程序mActivityStarter.startHomeActivityLocked(intent, aInfo, reason);}} else {Slog.wtf(TAG, "No home screen found for " + intent, new Throwable());}return true;
}
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一般情况下，被启动的应用就是 Launcher，因为 Launcher 的 Manifest 文件中有匹配了 Action 为 Intent.ACTION_MAIN，Category 为 Intent.CATEGORY_HOME 的 Activity。

<manifest xmlns:android="http://schemas.android.com/apk/res/android"package="com.android.launcher3"><uses-sdk android:targetSdkVersion="23" android:minSdkVersion="21"/>
...<applicationandroid:backupAgent="com.android.launcher3.LauncherBackupAgent"android:fullBackupOnly="true"android:fullBackupContent="@xml/backupscheme"android:hardwareAccelerated="true"android:icon="@mipmap/ic_launcher_home"android:label="@string/derived_app_name"android:largeHeap="@bool/config_largeHeap"android:restoreAnyVersion="true"android:supportsRtl="true" ><activityandroid:name="com.android.launcher3.Launcher"android:launchMode="singleTask"android:clearTaskOnLaunch="true"android:stateNotNeeded="true"android:theme="@style/LauncherTheme"android:windowSoftInputMode="adjustPan"android:screenOrientation="nosensor"android:configChanges="keyboard|keyboardHidden|navigation"android:resumeWhilePausing="true"android:taskAffinity=""android:enabled="true"><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>
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但是，当首次开机时，被启动的应用就是设置向导，因为设置向导的 Manifest 文件中也有匹配了 Action 为 Intent.ACTION_MAIN，Category 为 Intent.CATEGORY_HOME 的 Activity，并且优先级高于 Launcher。

<manifest xmlns:android="http://schemas.android.com/apk/res/android"package="com.android.provision">...<application><activityandroid:name="DefaultActivity"android:theme="@android:style/Theme.Translucent.NoTitleBar.Fullscreen"android:excludeFromRecents="true"><intent-filter android:priority="1"><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.SETUP_WIZARD" /></intent-filter></activity></application>
</manifest>
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Launcher 的 Manifest 中 intent-filter 没有设置优先级，默认为 0；设置向导的 Manifest 中 intent-filter 的优先级为 1；所以在 resolveActivityInfo() 方法获取符合的应用时会优先获取到设置向导。

private ActivityInfo resolveActivityInfo(Intent intent, int flags, int userId) {ActivityInfo ai = null;ComponentName comp = intent.getComponent();try {if (comp != null) {// Factory test.ai = AppGlobals.getPackageManager().getActivityInfo(comp, flags, userId);} else {ResolveInfo info = AppGlobals.getPackageManager().resolveIntent(intent,intent.resolveTypeIfNeeded(mContext.getContentResolver()),flags, userId);if (info != null) {ai = info.activityInfo;}}} catch (RemoteException e) {// ignore}return ai;
}
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获取最优 Activity 的具体实现在 PackageManagerService 的 chooseBestActivity() 方法中。

三、priority 及 android.intent.category.SETUP_WIZARD

Manifest 中 Activity 的 intent-filter 的优先级设置只有系统应用才会生效，非系统应用会被 PackageManagerService 调整为 0。

/*** Adjusts the priority of the given intent filter according to policy.* <p>* <ul>* <li>The priority for non privileged applications is capped to '0'</li>* <li>The priority for protected actions on privileged applications is capped to '0'</li>* <li>The priority for unbundled updates to privileged applications is capped to the*      priority defined on the system partition</li>* </ul>* <p>* <em>NOTE:</em> There is one exception. For security reasons, the setup wizard is* allowed to obtain any priority on any action.*/
private void adjustPriority(List<PackageParser.Activity> systemActivities, ActivityIntentInfo intent) {...final boolean privilegedApp =((applicationInfo.privateFlags & ApplicationInfo.PRIVATE_FLAG_PRIVILEGED) != 0);if (!privilegedApp) {// non-privileged applications can never define a priority >0Slog.w(TAG, "Non-privileged app; cap priority to 0;"+ " package: " + applicationInfo.packageName+ " activity: " + intent.activity.className+ " origPrio: " + intent.getPriority());intent.setPriority(0);return;}if (systemActivities == null) {// the system package is not disabled; we're parsing the system partitionif (isProtectedAction(intent)) {if (mDeferProtectedFilters) {// We can't deal with these just yet. No component should ever obtain a// >0 priority for a protected actions, with ONE exception -- the setup// wizard. The setup wizard, however, cannot be known until we're able to// query it for the category CATEGORY_SETUP_WIZARD. Which we can't do// until all intent filters have been processed. Chicken, meet egg.// Let the filter temporarily have a high priority and rectify the// priorities after all system packages have been scanned.mProtectedFilters.add(intent);if (DEBUG_FILTERS) {Slog.i(TAG, "Protected action; save for later;"+ " package: " + applicationInfo.packageName+ " activity: " + intent.activity.className+ " origPrio: " + intent.getPriority());}return;} else {if (DEBUG_FILTERS && mSetupWizardPackage == null) {Slog.i(TAG, "No setup wizard;"+ " All protected intents capped to priority 0");}if (intent.activity.info.packageName.equals(mSetupWizardPackage)) {if (DEBUG_FILTERS) {Slog.i(TAG, "Found setup wizard;"+ " allow priority " + intent.getPriority() + ";"+ " package: " + intent.activity.info.packageName+ " activity: " + intent.activity.className+ " priority: " + intent.getPriority());}// setup wizard gets whatever it wantsreturn;}Slog.w(TAG, "Protected action; cap priority to 0;"+ " package: " + intent.activity.info.packageName+ " activity: " + intent.activity.className+ " origPrio: " + intent.getPriority());intent.setPriority(0);return;}}// privileged apps on the system image get whatever priority they requestreturn;}...
}
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在 adjustPriority 方法中，如果 packageName 为 mSetupWizardPackage 就不会调整其优先级，保持其 Manifest 中设置的优先级。mSetupWizardPackage 的值从 getSetupWizardPackageName() 方法中获取。

final @Nullable String mSetupWizardPackage;
...public PackageManagerService(Context context, Installer installer,boolean factoryTest, boolean onlyCore) {...mSetupWizardPackage = getSetupWizardPackageName();...
}private @Nullable String getSetupWizardPackageName() {final Intent intent = new Intent(Intent.ACTION_MAIN);intent.addCategory(Intent.CATEGORY_SETUP_WIZARD);final List<ResolveInfo> matches = queryIntentActivitiesInternal(intent, null,MATCH_SYSTEM_ONLY | MATCH_DIRECT_BOOT_AWARE | MATCH_DIRECT_BOOT_UNAWARE| MATCH_DISABLED_COMPONENTS,UserHandle.myUserId());if (matches.size() == 1) {return matches.get(0).getComponentInfo().packageName;} else {Slog.e(TAG, "There should probably be exactly one setup wizard; found " + matches.size()+ ": matches=" + matches);return null;}
}
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所以 mSetupWizardPackage 就是有添加了 Category 为 android.intent.category.SETUP_WIZARD 的 Activity 的应用。

四、设置向导完成

既然设置向导的优先级高于 Launcher，那每次开机时不是都会先启动设置向导么，为什么设置向导完成后再次开机直接进入了 Launcher？

因为设置向导在最后退出时会禁用掉添加了 Category 为 Intent.CATEGORY_HOME 的 Activity，所以 ActivityManagerService 在 resolveActivityInfo() 获取匹配的应用时就不会获取到设置向导，直接获取到了 Launcher。

// remove this activity from the package manager.
PackageManager pm = getPackageManager();
ComponentName name = new ComponentName(this, DefaultActivity.class);
pm.setComponentEnabledSetting(name, PackageManager.COMPONENT_ENABLED_STATE_DISABLED,PackageManager.DONT_KILL_APP);
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