Android Framework 常见解决方案（24）屏蔽FallbackHome,去除 Android正在启动，直接进入Launcher_android fallbackhome

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）

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 end
        getWindow().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.Stub
        implements 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_FINISHED
                            data, null, 0);
                    data.recycle();
                }
            } catch (RemoteException ex) {
                ProtoLog.e(WM_ERROR, "Boot completed: SurfaceFlinger is dead!");
            }
            */
            //AGS add end
 
            EventLogTags.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_FINISHED
                            data, null, 0);
                    data.recycle();
                }
            } catch (RemoteException ex) {
                Slog.e(TAG, "Boot completed: SurfaceFlinger is dead!");
            }
        }
        //AGS add end
        mLaunchRootTask = null;
    }
    //...
}