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

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; 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;
      }
      //...
  }

  
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