下拉狀態欄有個亮度的進度條，如果開啟了亮度自動調節開關，會隨著周圍光線變化，這個進度條也會隨著變化，接下來就是看看這個功能是如何實現的。

源碼版本

基于 Android 9.0 分析。

BrightnessDialog，位于：frameworks/base/packages/SystemUI/src/com/android/systemui/settings/BrightnessDialog.java

ToggleSliderView，位于：frameworks/base/packages/SystemUI/src/com/android/systemui/settings/ToggleSliderView.java

DisplayPowerController，位于：frameworks/base/services/core/java/com/android/server/display/DisplayPowerController.java

AutomaticBrightnessController，位于：frameworks/base/services/core/java/com/android/server/display/AutomaticBrightnessController.java

BrightnessMappingStrategy，

概述

狀態欄里亮度頁面是 BrightnessDialog，其中進度條設置是 ToggleSliderView，亮度自動調節主要是 DisplayPowerController 和 AutomaticBrightnessController 兩個類，當亮度發生變化時，如果關聯到 ToggleSliderView，用的是 ContentObserver，Uri 為 Settings.System.SCREEN_AUTO_BRIGHTNESS_ADJ。

源碼梳理1、BrightnessDialog#onCreate：

@Overrideprotected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); //省略部分代碼 mBrightnessController = new BrightnessController(this, icon, slider);}2、這里進行了 BrightnessController 初始化，來看下：

public BrightnessController(Context context, ImageView icon, ToggleSlider control) { //省略部分代碼 mBrightnessObserver = new BrightnessObserver(mHandler); //省略部分代碼}

又進行了 BrightnessObserver 初始化：

/** ContentObserver to watch brightness **/private class BrightnessObserver extends ContentObserver { //省略部分代碼 private final Uri BRIGHTNESS_FOR_VR_URI = Settings.System.getUriFor(Settings.System.SCREEN_BRIGHTNESS_FOR_VR); //Add By WuXiaolong for AutomaticBrightness private final Uri BRIGHTNESS_ADJ_URI = Settings.System.getUriFor(Settings.System.SCREEN_AUTO_BRIGHTNESS_ADJ); public BrightnessObserver(Handler handler) { super(handler); } @Override public void onChange(boolean selfChange) { onChange(selfChange, null); } @Override public void onChange(boolean selfChange, Uri uri) { if (selfChange) return; if (BRIGHTNESS_MODE_URI.equals(uri)) { mBackgroundHandler.post(mUpdateModeRunnable); mBackgroundHandler.post(mUpdateSliderRunnable); } //省略部分代碼 //Add By WuXiaolong for AutomaticBrightness else if (BRIGHTNESS_ADJ_URI.equals(uri) && mAutomatic) { mBackgroundHandler.post(mUpdateSliderRunnable); } else { mBackgroundHandler.post(mUpdateModeRunnable); mBackgroundHandler.post(mUpdateSliderRunnable); } for (BrightnessStateChangeCallback cb : mChangeCallbacks) { cb.onBrightnessLevelChanged(); } } public void startObserving() { final ContentResolver cr = mContext.getContentResolver(); cr.unregisterContentObserver(this); //省略部分代碼 cr.registerContentObserver(BRIGHTNESS_FOR_VR_URI,false, this, UserHandle.USER_ALL); //Add By WuXiaolong for AutomaticBrightness cr.registerContentObserver(BRIGHTNESS_ADJ_URI,false, this, UserHandle.USER_ALL); } public void stopObserving() { final ContentResolver cr = mContext.getContentResolver(); cr.unregisterContentObserver(this); }}

其實我目前下載的源碼，這塊功能是不全的，我已經加上了，哪里進行 BrightnessObserver 的 ContentObserver 注冊呢？

3、回到 BrightnessDialog#onStart：

@Overrideprotected void onStart() { super.onStart(); mBrightnessController.registerCallbacks(); MetricsLogger.visible(this, MetricsEvent.BRIGHTNESS_DIALOG);}4、調用mBrightnessController.registerCallbacks();最終走到 mStartListeningRunnable：

private final Runnable mStartListeningRunnable = new Runnable() { @Override public void run() { //BrightnessObserver 注冊 mBrightnessObserver.startObserving(); mUserTracker.startTracking(); // Update the slider and mode before attaching the listener so we don’t // receive the onChanged notifications for the initial values. mUpdateModeRunnable.run(); mUpdateSliderRunnable.run(); mHandler.sendEmptyMessage(MSG_ATTACH_LISTENER); }};

當亮度有變化時，會走 BrightnessObserver#onChange，最終走到：

private final Handler mHandler = new Handler() { @Override public void handleMessage(Message msg) { mExternalChange = true; try { switch (msg.what) {//省略部分代碼case MSG_UPDATE_SLIDER: updateSlider(msg.arg1, msg.arg2 != 0); break;//省略部分代碼default: super.handleMessage(msg); } } finally { mExternalChange = false; } }};

走 updateSlider方法，到 ：

private void animateSliderTo(int target) { if (!mControlValueInitialized) { // Don’t animate the first value since it’s default state isn’t mea mControl.setValue(target); mControlValueInitialized = true; } //省略部分代碼}5、跳到 ToggleSliderView#setValue：

@Overridepublic void setValue(int value) { //這里正是修改進度條 mSlider.setProgress(value); if (mMirror != null) { mMirror.setValue(value); }}

接下來就是看看亮度自動調節主要的兩個類 DisplayPowerController 和 AutomaticBrightnessController。DisplayPowerController 屬于 Display 模塊，其控制設備屏幕亮滅、背光、與Power關系密切，這里主要看下屏幕亮度的控制這方面的邏輯。

6、首先，在 DisplayManagerService 中初始化 DisplayPowerController，如下：

private final class LocalService extends DisplayManagerInternal { @Override public void initPowerManagement(final DisplayPowerCallbacks callbacks, Handler handler, SensorManager sensorManager) { synchronized (mSyncRoot) { //省略部分代碼 mDisplayPowerController = new DisplayPowerController( mContext, callbacks, handler, sensorManager, blanker); } mHandler.sendEmptyMessage(MSG_LOAD_BRIGHTNESS_CONFIGURATION); }7、接著看下 DisplayPowerController 構造方法，如下：

public DisplayPowerController(Context context, DisplayPowerCallbacks callbacks, Handler handler, SensorManager sensorManager, DisplayBlanker blanker) { //省略部分代碼 mUseSoftwareAutoBrightnessConfig = resources.getBoolean( com.android.internal.R.bool.config_automatic_brightness_available); //省略部分代碼 if (mUseSoftwareAutoBrightnessConfig) { //省略部分代碼 mBrightnessMapper = BrightnessMappingStrategy.create(resources); if (mBrightnessMapper != null) { mAutomaticBrightnessController = new AutomaticBrightnessController(this, handler.getLooper(), sensorManager, mBrightnessMapper, lightSensorWarmUpTimeConfig, mScreenBrightnessRangeMinimum, mScreenBrightnessRangeMaximum, dozeScaleFactor, lightSensorRate, initialLightSensorRate, brighteningLightDebounce, darkeningLightDebounce, autoBrightnessResetAmbientLuxAfterWarmUp, hysteresisLevels); } else { mUseSoftwareAutoBrightnessConfig = false; } } //省略部分代碼 mAutoBrightnessAdjustment = getAutoBrightnessAdjustmentSetting(); mTemporaryAutoBrightnessAdjustment = Float.NaN; //省略部分代碼}

由于亮屏之后屏幕自動亮度才會生效，所以在亮屏的時候，流程會走到 DisplayPowerController 中的核心函數 updatePowerState()：

private void updatePowerState() { // Update the power state request. //省略部分代碼 final boolean autoBrightnessAdjustmentChanged = updateAutoBrightnessAdjustment(); if (autoBrightnessAdjustmentChanged) { mTemporaryAutoBrightnessAdjustment = Float.NaN; } // Use the autobrightness adjustment override if set. final float autoBrightnessAdjustment; if (!Float.isNaN(mTemporaryAutoBrightnessAdjustment)) { autoBrightnessAdjustment = mTemporaryAutoBrightnessAdjustment; mAppliedTemporaryAutoBrightnessAdjustment = true; } else { autoBrightnessAdjustment = mAutoBrightnessAdjustment; mAppliedTemporaryAutoBrightnessAdjustment = false; } boolean hadUserBrightnessPoint = false; // Configure auto-brightness. if (mAutomaticBrightnessController != null) { hadUserBrightnessPoint = mAutomaticBrightnessController.hasUserDataPoints(); mAutomaticBrightnessController.configure(autoBrightnessEnabled,mBrightnessConfiguration,mLastUserSetScreenBrightness / (float) PowerManager.BRIGHTNESS_ON,userSetBrightnessChanged, autoBrightnessAdjustment,autoBrightnessAdjustmentChanged, mPowerRequest.policy); } // Apply auto-brightness. boolean slowChange = false; if (brightness < 0) { float newAutoBrightnessAdjustment = autoBrightnessAdjustment; if (autoBrightnessEnabled) { brightness = mAutomaticBrightnessController.getAutomaticScreenBrightness(); newAutoBrightnessAdjustment = mAutomaticBrightnessController.getAutomaticScreenBrightnessAdjustment(); } if (brightness >= 0) { // Use current auto-brightness value and slowly adjust to changes. brightness = clampScreenBrightness(brightness); if (mAppliedAutoBrightness && !autoBrightnessAdjustmentChanged) {slowChange = true; // slowly adapt to auto-brightness } // Tell the rest of the system about the new brightness. Note that we do this // before applying the low power or dim transformations so that the slider // accurately represents the full possible range, even if they range changes what // it means in absolute terms. putScreenBrightnessSetting(brightness); mAppliedAutoBrightness = true; } else { mAppliedAutoBrightness = false; } if (autoBrightnessAdjustment != newAutoBrightnessAdjustment) { // If the autobrightness controller has decided to change the adjustment value // used, make sure that’s reflected in settings. putAutoBrightnessAdjustmentSetting(newAutoBrightnessAdjustment); } } else { mAppliedAutoBrightness = false; } //省略部分代碼}

接下來分別看看 autoBrightnessAdjustment 和 newAutoBrightnessAdjustment 怎么來的？

autoBrightnessAdjustment 是來自 mTemporaryAutoBrightnessAdjustment 或 mAutoBrightnessAdjustment 賦值，mAutoBrightnessAdjustment 在第 7 步mAutoBrightnessAdjustment = getAutoBrightnessAdjustmentSetting();有初始化，看下 getAutoBrightnessAdjustmentSetting()：

private float getAutoBrightnessAdjustmentSetting() { final float adj = Settings.System.getFloatForUser(mContext.getContentResolver(), Settings.System.SCREEN_AUTO_BRIGHTNESS_ADJ, 0.0f, UserHandle.USER_CURRENT); return Float.isNaN(adj) ? 0.0f : clampAutoBrightnessAdjustment(adj);}

繼續看下 clampAutoBrightnessAdjustment：

private static float clampAutoBrightnessAdjustment(float value) { return MathUtils.constrain(value, -1.0f, 1.0f);}

這里注意下 MathUtils.constrain() 表示百分比縮放函數，比如 MathUtils.constrain(0.5, 0, 255) 表示 （255-0）*0.5。

這樣了解了 autoBrightnessAdjustment，接下來看 newAutoBrightnessAdjustment。

8、回到 DisplayPowerController#updatePowerState()，

看到 newAutoBrightnessAdjustment 調用了 AutomaticBrightnessController.getAutomaticScreenBrightnessAdjustment()，最終是到了 BrightnessMapper#getAutoBrightnessAdjustment() 其中 mAutoBrightnessAdjustment 變量，賦值是在 BrightnessMapper#setAutoBrightnessAdjustment：

@Overridepublic boolean setAutoBrightnessAdjustment(float adjustment) { adjustment = MathUtils.constrain(adjustment, -1, 1); if (adjustment == mAutoBrightnessAdjustment) { return false; } if (DEBUG) { Slog.d(TAG, 'setAutoBrightnessAdjustment: ' + mAutoBrightnessAdjustment + ' => ' +adjustment); PLOG.start('auto-brightness adjustment'); } mAutoBrightnessAdjustment = adjustment; computeSpline(); return true;}9、BrightnessMapper#setAutoBrightnessAdjustment

這個方法調用又回到了 AutomaticBrightnessController#setAutoBrightnessAdjustment：

private boolean setAutoBrightnessAdjustment(float adjustment) { return mBrightnessMapper.setAutoBrightnessAdjustment(adjustment);}

AutomaticBrightnessController#setAutoBrightnessAdjustment調用是來到 AutomaticBrightnessController#configure()方法：

public void configure(boolean enable, @Nullable BrightnessConfiguration configuration, float brightness, boolean userChangedBrightness, float adjustment, boolean userChangedAutoBrightnessAdjustment, int displayPolicy) { // While dozing, the application processor may be suspended which will prevent us from // receiving new information from the light sensor. On some devices, we may be able to // switch to a wake-up light sensor instead but for now we will simply disable the sensor // and hold onto the last computed screen auto brightness. We save the dozing flag for // debugging purposes. boolean dozing = (displayPolicy == DisplayPowerRequest.POLICY_DOZE); boolean changed = setBrightnessConfiguration(configuration); changed |= setDisplayPolicy(displayPolicy); if (userChangedAutoBrightnessAdjustment) { changed |= setAutoBrightnessAdjustment(adjustment); } if (userChangedBrightness && enable) { // Update the brightness curve with the new user control point. It’s critical this // happens after we update the autobrightness adjustment since it may reset it. changed |= setScreenBrightnessByUser(brightness); } final boolean userInitiatedChange = userChangedBrightness || userChangedAutoBrightnessAdjustment; if (userInitiatedChange && enable && !dozing) { prepareBrightnessAdjustmentSample(); } changed |= setLightSensorEnabled(enable && !dozing); if (changed) { updateAutoBrightness(false /*sendUpdate*/); }}

AutomaticBrightnessController#configure()調用來到了 DisplayPowerController #updatePowerState()。

這樣也知道了 newAutoBrightnessAdjustment，繼續 putAutoBrightnessAdjustmentSetting：

private void putAutoBrightnessAdjustmentSetting(float adjustment) { mAutoBrightnessAdjustment = adjustment; Settings.System.putFloatForUser(mContext.getContentResolver(), Settings.System.SCREEN_AUTO_BRIGHTNESS_ADJ, adjustment, UserHandle.USER_CURRENT);}

就調到第 4 步 BrightnessObserver#onChange，進度條隨之變化，Over！

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