[b]屏幕亮度自动调节[/b]： 主要是从Sensor分析之中分离出来分析LIGHT 光线感应器，因此就分析一下自动调节屏幕亮度（手机随着光线的强度自我调节，也就是在亮的光线下屏幕自动调亮一些，暗的时候就自动调暗一些，省得光线对眼睛有刺激）.....     (本人从历经挫折才大概了解流程)，现在就开始讲一下流程，如果有不对地方希望牛人指出来。。。     先从Sttings入手吧，在diaplay中有屏幕亮度调节，有一个进度调，上面有一个checkbox（自动调节屏幕亮度的）， [img]http://files.jb51.net/file_images/article/201211/20121122160445194.png[/img] 那么我们当然去找settings下的文件开始看了，先找到 DiaplaySettings.java文件以及display_setting.xml文件，display_setting.xml里面能找到相应的组件，但是 在DiaplaySettings.java文件中却不能找到调用相应组件的代码， 那么我们再到settings中去找，能找到BrightnessPreference.java文件，没错这个文件就是自动调节亮度的文件，我们先看看代码： 构造函数中有mAutomaticAvailable = context.getResources().getBoolean(com.android.internal.R.bool.config_automatic_brightness_available); 开始以为mAutomaticAvailabl的值（为true，在config.xml中）是判断是否自动调节亮度，因为在我跟进到PowerManagerService.java中，在initInThread() 中   mUseSoftwareAutoBrightness = resources.getBoolean(                 com.android.internal.R.bool.config_automatic_brightness_available);         if (mUseSoftwareAutoBrightness) {             mAutoBrightnessLevels = resources.getIntArray(                     com.android.internal.R.array.config_autoBrightnessLevels);//得到自动化调节的值调用 getAutoBrightnessValue(int sensorValue, int[] values) 方法             mLcdBacklightValues = resources.getIntArray(                     com.android.internal.R.array.config_autoBrightnessLcdBacklightValues);             mButtonBacklightValues = resources.getIntArray(                     com.android.internal.R.array.config_autoBrightnessButtonBacklightValues);             mKeyboardBacklightValues = resources.getIntArray(。。。。。 。。。。。。这里看起来好像是当mUseSoftwareAutoBrightness为true时就取得config.xml文件config_autoBrightnessLevels的值，再去根据光线自动调节，但是mAutomaticAvailabl的值只是说明有没有自动调节屏幕的功能（比如说你将config.xml文件的config_automatic_brightness_available的值改为false，编译替换framework-res.apk那么在屏幕亮度调节中将没有自动调节的checkbox），这也能解释构造函数一开始就初始化mAutomaticAvailabl的值。 接下来在BrightnessPreference.java文件中有onProgressChanged，onStartTrackingTouch(SeekBar seekBar)，onStopTrackingTouch(SeekBar seekBar)方法，这些一看也能懂就不介绍了，在onBindDialogView(View view)方法中有 mCheckBox = (CheckBox)view.findViewById(R.id.automatic_mode);         if (mAutomaticAvailable) {//当有自动调节功能             mCheckBox.setOnCheckedChangeListener(this);//为checkbox添加监听事件             try {                 mOldAutomatic = Settings.System.getInt(getContext().getContentResolver(),                         Settings.System.SCREEN_BRIGHTNESS_MODE); 。。。。。。 主要看public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {         setMode(isChecked ? Settings.System.SCREEN_BRIGHTNESS_MODE_AUTOMATIC                 : Settings.System.SCREEN_BRIGHTNESS_MODE_MANUAL);         if (!isChecked) {             setBrightness(mSeekBar.getProgress() + MINIMUM_BACKLIGHT);         }     } 这里才是你选择自动调节亮度的checkbox，如果选择则setMode（Settings.System.SCREEN_BRIGHTNESS_MODE_AUTOMATIC）；并将数据存放到[url=http://www.1sucai.cn/database/]数据库[/url]中。 这里是重点：这里有个数据库，当监测到数据库中的值发生改变时也就是变为Settings.System.SCREEN_BRIGHTNESS_MODE_AUTOMATIC时，就会跳到 powerManagerService.java的initInThread()中ContentResolver resolver = mContext.getContentResolver();         Cursor settingsCursor = resolver.query(Settings.System.CONTENT_URI, null,                 "(" + Settings.System.NAME + "=?) or ("                         + Settings.System.NAME + "=?) or ("                         + Settings.System.NAME + "=?) or ("                         + Settings.System.NAME + "=?) or ("                         + Settings.System.NAME + "=?) or ("                         + Settings.System.NAME + "=?) or ("                         + Settings.System.NAME + "=?)",                 new String[]{STAY_ON_WHILE_PLUGGED_IN, SCREEN_OFF_TIMEOUT, DIM_SCREEN, XEC_DLS_CONTROL,                         SCREEN_BRIGHTNESS_MODE, WINDOW_ANIMATION_SCALE, TRANSITION_ANIMATION_SCALE},                 null);         mSettings = new ContentQueryMap(settingsCursor, Settings.System.NAME, true, mHandler);         SettingsObserver settingsObserver = new SettingsObserver();         mSettings.addObserver(settingsObserver); 数据库中数据发生改变时触发事件的发生。 在 powerManagerService.java的systemReady()（只在开机调用一次就不再调用）中  if (mUseSoftwareAutoBrightness) {             Log.i("frist","frist="+"aaaa");             mLightSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_LIGHT);             enableLightSensor(true);         } 而mUseSoftwareAutoBrightness是在initInThread()线程中取得了true值，那么就到enableLightSensor(true);方法去看  if (enable) {                     mSensorManager.registerListener(mLightListener, mLightSensor,                             SensorManager.SENSOR_DELAY_NORMAL);                 } 如果传递来的值为true也就是enable=true就监听而且用匹配屏幕方向变化的感应SENSOR_DELAY_NORMAL。 再看mLightListener事件：SensorEventListener mLightListener = new SensorEventListener() {         public void onSensorChanged(SensorEvent event) {             synchronized (mLocks) {                 int value = (int)event.values[0];//从event里面获取当前数据                 Log.i("value","value="+value);                        long milliseconds = SystemClock.elapsedRealtime();                 if (mDebugLightSensor) {                     Slog.d(TAG, "onSensorChanged: light value: " + value);                 }                 mHandler.removeCallbacks(mAutoBrightnessTask);                 if (mLightSensorValue != value) {//mLightSensorValue是当前的屏幕亮度                     if (mLightSensorValue == -1 ||                             milliseconds < mLastScreenOnTime + mLightSensorWarmupTime) {                         // process the value immediately if screen has just turned on                         lightSensorChangedLocked(value);                     } else {                         // delay processing to debounce the sensor                         mLightSensorPendingValue = value;//mLightSensorPendingValue是准备要设置的亮度                         mHandler.postDelayed(mAutoBrightnessTask, LIGHT_SENSOR_DELAY);//到mAutoBrightnessTask线程去完成自动调节                     }                 } else {                     mLightSensorPendingValue = -1;                 }             }         } 当前屏幕亮度肯定不等与-1，所以做else中的mHandler.postDelayed(mAutoBrightnessTask, LIGHT_SENSOR_DELAY)，那么我们再到mAutoBrightnessTask 线程看：private Runnable mAutoBrightnessTask = new Runnable() {         public void run() {             synchronized (mLocks) {                 int value = (int)mLightSensorPendingValue;                 Log.i("mLightSensorPendingValue","mLightSensorPendingValue"+mLightSensorPendingValue);                 if (value >= 0) {                     mLightSensorPendingValue = -1;                     lightSensorChangedLocked(value);                 }             }         }     };就是不断的去调用lightSensorChangedLocked(value) private void lightSensorChangedLocked(int value) { 。。。。。。。 if (mLightSensorValue != value) {             mLightSensorValue = value;             if ((mPowerState & BATTERY_LOW_BIT) == 0) {                 // Use light sensor value no matter it is in a dock or not.                 int lcdValue = getAutoBrightnessValue(                         value,                         mLcdBacklightValues);// 取得mLcdBacklightValues里面的值                 int buttonValue = getAutoBrightnessValue(value, mButtonBacklightValues);                 int keyboardValue;                 if (mKeyboardVisible) {                     keyboardValue = getAutoBrightnessValue(value, mKeyboardBacklightValues);                 } else {                     keyboardValue = 0;                 } 。。。 if (mAutoBrightessEnabled && mScreenBrightnessOverride < 0) {//设置屏幕亮度                     mScreenBrightness.setTargetLocked(lcdValue, AUTOBRIGHTNESS_ANIM_STEPS,                             INITIAL_SCREEN_BRIGHTNESS, (int)mScreenBrightness.curValue);                 } 。。。。。    }