源码：
base\services\core\java\com\android\server\display\DisplayPowerState.java
功能：
对上：提供mProperty.setValue方法调用，接收brightness
对下：调用LightsService.setBrightness方法，设置brightness
源码分析：
构建了mProperty.setValue这个方法供调用，传入brightness值
public static final IntProperty<DisplayPowerState> SCREEN_BRIGHTNESS = new IntProperty<DisplayPowerState>("screenBrightness") { public void setValue(DisplayPowerState object, int value) object.setScreenBrightness(value); // DisplayPowerState.setScreenBrightness mScreenBrightness = brightness; scheduleScreenUpdate(); postScreenUpdateThreadSafe(); mHandler.post(mScreenUpdateRunnable); // 执行mScreenUpdateRunnable.run() brightness = mScreenBrightness; mPhotonicModulator.setState(mScreenState, brightness); mPendingBacklight = backlight; // brightness最终保存在PhotonicModulator.mPendingBacklight mLock.notifyAll(); // 唤醒PhotonicModulator线程
notifyAll将唤醒PhotonicModulator线程，最终调用LightsService.setBrightness，该函数功能请查看LightsService篇
public void run() { for (;;) { backlight = mPendingBacklight; backlightChanged = (backlight != mActualBacklight); if (!stateChanged && !backlightChanged) { mLock.wait(); // 等待 continue; } mActualBacklight = backlight; // 更新数据 if (backlightChanged) setBrightness(backlight); mBacklight.setBrightness(backlight); // mLights[LIGHT_ID_BACKLIGHT].setBrightness(backlight) } }
