1 原理说明

开机以后，设备会有一个“android正在启动”这样的弹框，这个界面是一个叫FallbackHome的Activity来展示的。FallbackHome机制是Android系统启动过程中的一种降级处理机制。当系统启动时，如果默认的Launcher应用无法正常加载或出现错误，系统会自动启用FallbackHome来替代默认Launcher。但一般为了改善产品体验，最终决定移除弹窗页面，直接进入默认的Launcher，避免弹窗对用户界面的干扰。具体而言，FallbackHome机制包括以下内容：

• 默认Launcher故障检测：系统会检测默认的Launcher应用是否能够正常加载和运行。如果检测到故障，系统将启动FallbackHome。
• 解锁过程中的弹窗：在系统解锁之前，可能会出现一个"Android正在启动"的弹窗页面，用于指示系统正在加载和准备。这个弹窗页面通常出现在桌面壁纸上，用户需要等待系统完全解锁后才能进入默认的Launcher。

去掉FallbackHome的效果实际上是让FallbackHome的view不显示，然后开机启动动画延长一下，直到系统解锁后再停止开机动画，完成这样较为顺滑的过渡。

2 修改方案（Android Q R S）

如果只是需要将FallbackHome去掉，黑屏但是不做任何处理，实测时间较短，则只需要改@1即可。如果不是前面这种情况，那么就需要修改@2和@3了。具体修改方案如下（这里以S版本修改为主，Q和R有一些差异但原理不变）：

@1 修改文件为：AOSP/packages/apps/Settings$ vim src/com/android/settings/FallbackHome.java，目的为FallbackHome不显示View，所以注释掉。修改内容为：

public class FallbackHome extends Activity {private static final String TAG = "FallbackHome";private static final int PROGRESS_TIMEOUT = 2000;private boolean mProvisioned;private WallpaperManager mWallManager;private final Runnable mProgressTimeoutRunnable = () -> {//AGS add start//不显示任何内容，如果是黑色衔接，直接改这里就足够了，如果不是则需要 2，3步骤内容的修改/*  View v = getLayoutInflater().inflate(R.layout.fallback_home_finishing_boot, null);setContentView(v);v.setAlpha(0f);v.animate().alpha(1f).setDuration(500).setInterpolator(AnimationUtils.loadInterpolator(this, android.R.interpolator.fast_out_slow_in)).start();*///AGS add endgetWindow().addFlags(LayoutParams.FLAG_KEEP_SCREEN_ON);};//...
}

@2 修改文件为：AOSP/frameworks/base/services/core/java/com/android/server/wm/WindowManagerService.java，目的为播放完开机动画后不退出开机动画，所以注释掉即可。修改内容为：

public class WindowManagerService extends IWindowManager.Stubimplements Watchdog.Monitor, WindowManagerPolicy.WindowManagerFuncs {//...private void performEnableScreen() {synchronized (mGlobalLock) {ProtoLog.i(WM_DEBUG_BOOT, "performEnableScreen: mDisplayEnabled=%b"+ " mForceDisplayEnabled=%b" + " mShowingBootMessages=%b"+ " mSystemBooted=%b mOnlyCore=%b. %s", mDisplayEnabled,mForceDisplayEnabled, mShowingBootMessages, mSystemBooted, mOnlyCore,new RuntimeException("here").fillInStackTrace());if (mDisplayEnabled) {return;}if (!mSystemBooted && !mShowingBootMessages) {return;}if (!mShowingBootMessages && !mPolicy.canDismissBootAnimation()) {return;}// Don't enable the screen until all existing windows have been drawn.if (!mForceDisplayEnabled) {if (mBootWaitForWindowsStartTime < 0) {// First time we will start waiting for all windows to be drawn.mBootWaitForWindowsStartTime = SystemClock.elapsedRealtime();}for (int i = mRoot.getChildCount() - 1; i >= 0; i--) {if (mRoot.getChildAt(i).shouldWaitForSystemDecorWindowsOnBoot()) {return;}}long waitTime = SystemClock.elapsedRealtime() - mBootWaitForWindowsStartTime;mBootWaitForWindowsStartTime = -1;if (waitTime > 10) {ProtoLog.i(WM_DEBUG_BOOT,"performEnableScreen: Waited %dms for all windows to be drawn",waitTime);}}//AGS add start//播放完开机动画后不退出开机动画,注释掉如下代码即可。/*if (!mBootAnimationStopped) {Trace.asyncTraceBegin(TRACE_TAG_WINDOW_MANAGER, "Stop bootanim", 0);// stop boot animation// formerly we would just kill the process, but we now ask it to exit so it// can choose where to stop the animation.SystemProperties.set("service.bootanim.exit", "1");mBootAnimationStopped = true;}if (!mForceDisplayEnabled && !checkBootAnimationCompleteLocked()) {ProtoLog.i(WM_DEBUG_BOOT, "performEnableScreen: Waiting for anim complete");return;}try {IBinder surfaceFlinger = ServiceManager.getService("SurfaceFlinger");if (surfaceFlinger != null) {ProtoLog.i(WM_ERROR, "******* TELLING SURFACE FLINGER WE ARE BOOTED!");Parcel data = Parcel.obtain();data.writeInterfaceToken("android.ui.ISurfaceComposer");surfaceFlinger.transact(IBinder.FIRST_CALL_TRANSACTION, // BOOT_FINISHEDdata, null, 0);data.recycle();}} catch (RemoteException ex) {ProtoLog.e(WM_ERROR, "Boot completed: SurfaceFlinger is dead!");}*///AGS add endEventLogTags.writeWmBootAnimationDone(SystemClock.uptimeMillis());Trace.asyncTraceEnd(TRACE_TAG_WINDOW_MANAGER, "Stop bootanim", 0);mDisplayEnabled = true;ProtoLog.i(WM_DEBUG_SCREEN_ON, "******************** ENABLING SCREEN!");// Enable input dispatch.mInputManagerCallback.setEventDispatchingLw(mEventDispatchingEnabled);}try {mActivityManager.bootAnimationComplete();} catch (RemoteException e) {}mPolicy.enableScreenAfterBoot();// Make sure the last requested orientation has been applied.updateRotationUnchecked(false, false);}//...
}

@3 修改文件为：AOSP/frameworks/base/services/core/java/com/android/server/wm/ActivityRecord.java，目的为解锁后再结束开机动画。修改内容为：

public final class ActivityRecord extends WindowToken implements WindowManagerService.AppFreezeListener {
/** Called when the windows associated app window container are drawn. *///...private void onWindowsDrawn(long timestampNs) {if (mPerf != null && perfActivityBoostHandler > 0) {mPerf.perfLockReleaseHandler(perfActivityBoostHandler);perfActivityBoostHandler = -1;} else if (perfActivityBoostHandler > 0) {Slog.w(TAG, "activity boost didn't release as expected");}final TransitionInfoSnapshot info = mTaskSupervisor.getActivityMetricsLogger().notifyWindowsDrawn(this, timestampNs);final boolean validInfo = info != null;final int windowsDrawnDelayMs = validInfo ? info.windowsDrawnDelayMs : INVALID_DELAY;final @WaitResult.LaunchState int launchState =validInfo ? info.getLaunchState() : WaitResult.LAUNCH_STATE_UNKNOWN;// The activity may have been requested to be invisible (another activity has been launched)// so there is no valid info. But if it is the current top activity (e.g. sleeping), the// invalid state is still reported to make sure the waiting result is notified.if (validInfo || this == getDisplayArea().topRunningActivity()) {mTaskSupervisor.reportActivityLaunched(false /* timeout */, this,windowsDrawnDelayMs, launchState);}finishLaunchTickingLocked();if (task != null) {task.setHasBeenVisible(true);}//AGS add start/*if (isHomeIntent(intent) && shortComponentName != null && !shortComponentName.contains("FallbackHome")) {SystemProperties.set("service.bootanim.exit", "1");//这里就是将上面注掉的代码copy过来try {IBinder surfaceFlinger = ServiceManager.getService("SurfaceFlinger");if (surfaceFlinger != null) {Slog.i(TAG_WM, "******* TELLING SURFACE FLINGER WE ARE BOOTED!");Parcel data = Parcel.obtain();data.writeInterfaceToken("android.ui.ISurfaceComposer");surfaceFlinger.transact(IBinder.FIRST_CALL_TRANSACTION, // BOOT_FINISHEDdata, null, 0);data.recycle();}} catch (RemoteException ex) {Slog.e(TAG, "Boot completed: SurfaceFlinger is dead!");}}*///AGS add endmLaunchRootTask = null;}//...
}