Android中所有系统的定义：lights.h -------------------------- #define LIGHT_ID_BACKLIGHT "backlight" JNI: com_android_server_lights_LightsService.cpp --------------------------- setLight_native：调用HAL去控制背光 Service：LightsService.java ------------------------------- 1.它是各种灯光和背光的Service，提供了对背光灯操作的所有方法 2.setLightLocked()：是实际调用JNI操作背光灯的函数，所有向应用程序公开的LCD操作接口都使用synchronized (this){... setLightLocked() ...} 确保互斥访问硬件。 3.onStart()中：publishLocalService(LightsManager.class, mService); DisplayPowerController.java ---------------------------------- 1.获取LightsService中注册的LightsManager：mLights = LocalServices.getService(LightsManager.class); 2.然后在构造函数中只获取了背光灯：new DisplayPowerState(mBlanker, mLights.getLight(LightsManager.LIGHT_ID_BACKLIGHT), new ColorFade(Display.DEFAULT_DISPLAY)); 整个系统中也只有这里获取了背光灯。 DisplayPowerState.java ----------------------------------- DisplayPowerState(DisplayBlanker blanker, Light backlight, ColorFade electronBeam) --> mPhotonicModulator = new PhotonicModulator(); --> mPhotonicModulator.start(); --> run() //无限循环执行这个线程 --> mLock.wait(); //睡眠 --> setBrightness(backlight); 在setState()中notifyAll(); //唤醒 在mScreenUpdateRunnable中调用了setState() private final Runnable mScreenUpdateRunnable = new Runnable() { mPhotonicModulator.setState(mScreenState, brightness); } mScreenUpdateRunnable作为一个处理消息的响应线程 postScreenUpdateThreadSafe中mHandler.post(mScreenUpdateRunnable); scheduleScreenUpdate() --> postScreenUpdateThreadSafe(); 由上，也就是调用scheduleScreenUpdate()来触发向消息队列中存放一个消息，消息处理函数中notifyAll()然后在上面无限循环的 run()中设置背光亮度。 DisplayPowerState --> scheduleScreenUpdate setScreenState --> scheduleScreenUpdate setScreenBrightness --> scheduleScreenUpdate setColorFadeLevel --> scheduleScreenUpdate DisplayPowerController.java ------------------------- --> new DisplayPowerState() --> animateScreenStateChange //在updatePowerState中被调用 处理消息： Handler的handleMessage中调用updatePowerState updatePowerState() animateScreenStateChange //这里面设置背光亮度 发送消息： requestPowerState sendUpdatePowerStateLocked //基本上所有操作都是通过它执行的，也就是这个函数对上层做基础支持。 mHandler.sendMessage(msg); //它通过发送消息在Handler的handleMessage中处理 updateDisplayPowerStateLocked requestPowerState 什么时候发消息： PowerManagerService.java ---------------------------- updatePowerStateLocked updateDisplayPowerStateLocked systemReady方法中： (1)注册了4个Receiver eg: filter.addAction(Intent.ACTION_BATTERY_CHANGED); filter.setPriority(IntentFilter.SYSTEM_HIGH_PRIORITY); mContext.registerReceiver(new BatteryReceiver(), filter, null, mHandler); 当数据库中的Intent.ACTION_BATTERY_CHANGED变化的时候，BatteryReceiver的onReceive()就会被调用。 (2)对于背光灯还注册了1个ContentObserver resolver.registerContentObserver(Settings.Secure.getUriFor( Settings.Secure.SCREENSAVER_ENABLED), false, mSettingsObserver, UserHandle.USER_ALL); 当数据库中Settings.Secure.SCREENSAVER_ENABLED变化的时候，mSettingsObserver中的onChange()方法就会被调用。 Receiver 监听的事件 BatteryReceiver ACTION_BATTERY_CHANGED DreamReceiver ACTION_DREAMING_STARTED UserSwitchedReceiver ACTION_USER_SWITCHED DockReceiver ACTION_DOCK_EVENT mSettingsObserver SCREENSAVER_ENABLED 屏保功能开启 SCREENSAVER_ACTIVATE_ON_SLEEP 在睡眠时屏保启动 SCREENSAVER_ACTIVATE_ON_DOCK 连接底座并且屏保启动 SCREEN_OFF_TIMEOUT 进入dream状态前未活动时间 SLEEP_TIMEOUT 进入sleep状态前未活动时间 STAY_ON_WHILE_PLUGGED_IN 有插入并且屏幕开启 SCREEN_BRIGHTNESS 屏幕亮度 SCREEN_BRIGHTNESS_MODE 屏幕亮度模式 SCREEN_AUTO_BRIGHTNESS_ADJ LOW_POWER_MODE LOW_POWER_MODE_TRIGGER_LEVEL
2.使用到内容观察者模式
使用方法： 1.创建一个 ContentObserver 的子类，实现 onChange() 方法。 private final class SettingsObserver extends ContentObserver { public SettingsObserver(Handler handler) { super(handler); } /*目的是复写这个onChange方法*/ @Override public void onChange(boolean selfChange, Uri uri) { synchronized (mLock) { /*它里面也是去调用updatePowerStateLocked*/ handleSettingsChangedLocked(); } } } 2.注册 ContentObserver /* arg1：需要监听的 uri。 arg2：为 false 表示精确匹配，即只匹配该 Uri。为 true 表示可以同时匹配其派生的 Uri，如： content://com.qin.cb/student（精确匹配） content://com.qin.cb/student/# （派生，false 才能匹配到） content://com.qin.cb/student/schoolchild（派生，false 才能匹配到） arg3：ContentObserver 的实例。 */ registerContentObserver(Settings.Secure.getUriFor(Settings.Secure.SCREENSAVER_ENABLED), false, mSettingsObserver, UserHandle.USER_ALL); 3.用完后记得取消注册 ContentObserver unregisterContentObserver(myContentObserver) 参考： ContentObserver：https://www.jianshu.com/p/3bc164010b5f
3.App测试Demo MainActivity.java
package com.example.mm.lcd_brightness; import android.os.Bundle; import android.provider.Settings; import android.support.design.widget.FloatingActionButton; import android.support.design.widget.Snackbar; import android.support.v7.app.AppCompatActivity; import android.support.v7.widget.Toolbar; import android.util.Log; import android.view.View; import android.view.Menu; import android.view.MenuItem; import android.widget.SeekBar; public class MainActivity extends AppCompatActivity { final private int LED_NOTIFICATION_ID = 123; private SeekBar mBacklightSeekBar = null; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); Toolbar toolbar = findViewById(R.id.toolbar); setSupportActionBar(toolbar); mBacklightSeekBar = (SeekBar)findViewById(R.id.seekBar); try { /*将背光调节模式改为手动，无为自动的话手动调节无效*/ Settings.System.putInt(getContentResolver(), Settings.System.SCREEN_BRIGHTNESS_MODE, Settings.System.SCREEN_BRIGHTNESS_MODE_MANUAL); /*让滚动条的初始状态显示在正确的位置*/ int brightness = android.provider.Settings.System.getInt(getContentResolver(), android.provider.Settings.System.SCREEN_BRIGHTNESS); mBacklightSeekBar.setProgress(brightness*100/255); } catch (Settings.SettingNotFoundException e) { e.printStackTrace(); } /*设置滚动条的监听函数*/ mBacklightSeekBar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener (){ @Override public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) { int brightness = mBacklightSeekBar.getProgress(); /*应用程序传入的是0--100，而底层是0--255*/ brightness = brightness * 255 / 100; /*设置到数据库中，会导致内容观察者对应的设置屏幕亮度的方法被调用*/ android.provider.Settings.System.putInt(getContentResolver(), android.provider.Settings.System.SCREEN_BRIGHTNESS, brightness); } @Override public void onStartTrackingTouch(SeekBar seekBar) { Log.d("App_Brightness: ","==============onStartTrackingTouch==============="); } @Override public void onStopTrackingTouch(SeekBar seekBar) { Log.d("App_Brightness: ","==============onStartTrackingTouch==============="); } }); } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.menu_main, menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { // Handle action bar item clicks here. The action bar will // automatically handle clicks on the Home/Up button, so long // as you specify a parent activity in AndroidManifest.xml. int id = item.getItemId(); //noinspection SimplifiableIfStatement if (id == R.id.action_settings) { return true; } return super.onOptionsItemSelected(item); } }