android4.4 车载灭屏按任意键及触摸屏幕恢复亮屏

车载上的android4.4系统，基本上常亮。但最近需要一个新功能可以在launcher新增一个按钮，点击的时候。屏幕亮度为0，但实际上不等于按power键，不会睡眠。

然后可以按任意键恢复亮度，包括触屏事件。

一、PowerManagerService原先屏幕亮度流程

PowerManagerService是通过updateDisplayPowerStateLocked函数，把亮度更新到DisplayPowerController那块，然后再去调用lightsService获取背光的light，再去设置背景光的亮度。

但是这有问题，在PowerManagerService的updateDisplayPowerStateLocked函数，通常有个最低的亮度值(一般为10)，如果低于这个亮度还是为这个值。

所以调用PowerManager的setBacklightBrightness，哪怕设的为0，最终亮度也为10.

    private void updateDisplayPowerStateLocked(int dirty) {if ((dirty & (DIRTY_WAKE_LOCKS | DIRTY_USER_ACTIVITY | DIRTY_WAKEFULNESS| DIRTY_ACTUAL_DISPLAY_POWER_STATE_UPDATED | DIRTY_BOOT_COMPLETED| DIRTY_SETTINGS | DIRTY_SCREEN_ON_BLOCKER_RELEASED)) != 0) {int newScreenState = getDesiredScreenPowerStateLocked();if (newScreenState != mDisplayPowerRequest.screenState) {if (newScreenState == DisplayPowerRequest.SCREEN_STATE_OFF&& mDisplayPowerRequest.screenState!= DisplayPowerRequest.SCREEN_STATE_OFF) {mLastScreenOffEventElapsedRealTime = SystemClock.elapsedRealtime();}mDisplayPowerRequest.screenState = newScreenState;nativeSetPowerState(newScreenState != DisplayPowerRequest.SCREEN_STATE_OFF,newScreenState == DisplayPowerRequest.SCREEN_STATE_BRIGHT);}int screenBrightness = mScreenBrightnessSettingDefault;float screenAutoBrightnessAdjustment = 0.0f;boolean autoBrightness = (mScreenBrightnessModeSetting ==Settings.System.SCREEN_BRIGHTNESS_MODE_AUTOMATIC);if (isValidBrightness(mScreenBrightnessOverrideFromWindowManager)) {screenBrightness = mScreenBrightnessOverrideFromWindowManager;autoBrightness = false;} else if (isValidBrightness(mTemporaryScreenBrightnessSettingOverride)) {screenBrightness = mTemporaryScreenBrightnessSettingOverride;} else if (isValidBrightness(mScreenBrightnessSetting)) {screenBrightness = mScreenBrightnessSetting;}if (autoBrightness) {screenBrightness = mScreenBrightnessSettingDefault;if (isValidAutoBrightnessAdjustment(mTemporaryScreenAutoBrightnessAdjustmentSettingOverride)) {screenAutoBrightnessAdjustment =mTemporaryScreenAutoBrightnessAdjustmentSettingOverride;} else if (isValidAutoBrightnessAdjustment(mScreenAutoBrightnessAdjustmentSetting)) {screenAutoBrightnessAdjustment = mScreenAutoBrightnessAdjustmentSetting;}}screenBrightness = Math.max(Math.min(screenBrightness,//这个就是最小亮度的调整。mScreenBrightnessSettingMaximum), mScreenBrightnessSettingMinimum);screenAutoBrightnessAdjustment = Math.max(Math.min(screenAutoBrightnessAdjustment, 1.0f), -1.0f);mDisplayPowerRequest.screenBrightness = screenBrightness;mDisplayPowerRequest.screenAutoBrightnessAdjustment =screenAutoBrightnessAdjustment;mDisplayPowerRequest.useAutoBrightness = autoBrightness;mDisplayPowerRequest.useProximitySensor = shouldUseProximitySensorLocked();mDisplayPowerRequest.blockScreenOn = mScreenOnBlocker.isHeld();mDisplayReady = mDisplayPowerController.requestPowerState(mDisplayPowerRequest,mRequestWaitForNegativeProximity);//最终都是设置到DisplayPowerControllermRequestWaitForNegativeProximity = false;

二、PowerManagerService设置背光文件节点

因此我们的选择还是直接设置背光的文件节点，况且我们还要事先获取背光值，用来下次恢复亮度的时候，设置之前的亮度值。

代码如下我们再PowerManager中做了两个接口turnoffBacklight和turnOnBacklight来控制背光，最终通过binder调用到PowerManagerService中。

在PowerManagerService中直接通过了写节点/读节点的方式，来设置/获取背光。

    @Override // Binder callpublic void turnOffBacklight() {int lightBrightness = getBackLightBrightness();if (lightBrightness != 0) {mBackLightBrightness = getBackLightBrightness();setBackLightBrightness(0);}}@Override // Binder callpublic boolean turnOnBacklight() {int lightBrightness = getBackLightBrightness();if (lightBrightness == 0) {Slog.d(TAG, "turnOnBacklight setBackLightBrightness :" + mBackLightBrightness);setBackLightBrightness(mBackLightBrightness);return true;}return false;}private int getBackLightBrightness() {int level = -1;File localFile = new File("/sys/class/leds/lcd-backlight/brightness");if (!localFile.canRead()) {Slog.w(TAG, "/sys/class/leds/lcd-backlight can not read!");return level;}try {FileInputStream in = new FileInputStream(localFile);byte[] b = new byte[4];in.read(b);int count = 0;for (int i = 0; i < 4; i++) {if (b[i] >= '0' && b[i] <= '9') {//非数字去除count++;} else {break;}}String str = new String(b, 0, count);str = str.replaceAll("\\s+", "");//去除空格，换行符等level = Integer.parseInt(str);in.close();} catch (Exception e) {}return level;}private void setBackLightBrightness(int level) {File localFile = new File("/sys/class/leds/lcd-backlight/brightness");if (!localFile.canWrite()) {Slog.w(TAG, "/sys/class/leds/lcd-backlight can not write!");return;}try {FileOutputStream fos = new FileOutputStream(localFile);fos.write(String.valueOf(level).getBytes());fos.close();} catch (Exception e) {}}

我们再Launcher的按钮点击后调用PowerManager中的turnoffBacklight函数，灭屏。

三、恢复屏幕亮度

3.1 按键

最后我们在按键和触屏的时候恢复屏幕亮度，普通按键的流程会先到PhoneWindowManager的interceptKeyBeforeQueueing函数先处理，我们可以在这个函数中先进行背光亮度的判读, 部分代码如下：

    @Overridepublic int interceptKeyBeforeQueueing(KeyEvent event, int policyFlags, boolean isScreenOn) {if (!mSystemBooted) {// If we have not yet booted, don't let key events do anything.return 0;}if (mPowerManager.isScreenOn()) {if (mPowerManager.turnOnBacklight()) {return 0;}}.......

逻辑无非两种情况，调用mPowerManager.isScreenOn函数

1.如果isScreenOn是返回true的。因为PowerManagerService的流程没有改变，系统还认为屏幕是亮着的。

所以我们turnOnBacklight，如果这个时候屏幕的亮度为0，代表我们之前调用过turnoffBacklight函数把背景光亮度设置为0了，我们把它恢复的亮度，而函数turnOnBacklight返回true，在interceptKeyBeforeQueueing函数中直接return了，代表这次的按键就点亮屏幕了，不会走interceptKeyBeforeQueueing的后续流程了，返回0也不会最后传给用户了。

如果这个时候有亮度，代表之前没有调用turnoffBacklight，函数turnOnBacklight返回false，继续interceptKeyBeforeQueueing的原有流程。代表如果屏幕亮着，按键处理走自己的流程。

2.如果isScreenOn返回false，代表现在灭屏了。那么这是PowerManagerService的流程了，和我们的背景光无关。

3.2 触屏

触屏的话流程会有一个不一样，因为在NativeInputManager的interceptMotionBeforeQueueing函数中，只有当isScreenOn是false的时候才会调用上层的interceptMotionBeforeQueueingWhenScreenOff函数。也就是灭屏的时候才会到PhoneWindowManager的interceptMotionBeforeQueueingWhenScreenOff函数，而我们恰恰是要在PowerManagerService亮屏的时候，进行我们的逻辑。

void NativeInputManager::interceptMotionBeforeQueueing(nsecs_t when, uint32_t& policyFlags) {// Policy:// - Ignore untrusted events and pass them along.// - No special filtering for injected events required at this time.// - Filter normal events based on screen state.// - For normal events brighten (but do not wake) the screen if currently dim.if ((policyFlags & POLICY_FLAG_TRUSTED) && !(policyFlags & POLICY_FLAG_INJECTED)) {if (isScreenOn()) {policyFlags |= POLICY_FLAG_PASS_TO_USER;if (!isScreenBright()) {policyFlags |= POLICY_FLAG_BRIGHT_HERE;}} else {JNIEnv* env = jniEnv();jint wmActions = env->CallIntMethod(mServiceObj,gServiceClassInfo.interceptMotionBeforeQueueingWhenScreenOff,policyFlags);if (checkAndClearExceptionFromCallback(env,"interceptMotionBeforeQueueingWhenScreenOff")) {wmActions = 0;}policyFlags |= POLICY_FLAG_WOKE_HERE | POLICY_FLAG_BRIGHT_HERE;handleInterceptActions(wmActions, when, /*byref*/ policyFlags);}} else {policyFlags |= POLICY_FLAG_PASS_TO_USER;}
}

所以在PhoneWindowManager的interceptMotionBeforeQueueingWhenScreenOff函数处理不行，最后只能到应用进程处理，看我之前几篇分析按键的博客知道，触屏事件最终会调用到ViewRootImpl的各个InputStage中，而触屏和按键会走到ViewPostImeInputStage中去

    final class ViewPostImeInputStage extends InputStage {public ViewPostImeInputStage(InputStage next) {super(next);}@Overrideprotected int onProcess(QueuedInputEvent q) {if (q.mEvent instanceof KeyEvent) {return processKeyEvent(q);} else {// If delivering a new non-key event, make sure the window is// now allowed to start updating.handleDispatchDoneAnimating();final int source = q.mEvent.getSource();if ((source & InputDevice.SOURCE_CLASS_POINTER) != 0) {//触屏事件if (mPowerManager.isScreenOn()) {if (mPowerManager.turnOnBacklight()) {return FORWARD;}}return processPointerEvent(q);} else if ((source & InputDevice.SOURCE_CLASS_TRACKBALL) != 0) {return processTrackballEvent(q);} else {return processGenericMotionEvent(q);}}}

这里的话流程和按键那边的处理逻辑是一样的，就不分析了。

四、注意

有一点我们必须注意，手机如果要杀应用的话，输入法绝对不能杀，杀了输入法后，会导致输入法没有重启的这段时间，底层按键不能分发到上层应用。具体原因，后续分析。