小米的新版系统（大于MIUI9），取到的当前亮度值是远大于255的，应该是小米修改了系统亮度的最大值（不知道小米是出于什么原因修改的）。所以最大值要根据系统版本动态获取。

public static final int MAX_BRIGHTNESS_VALUE = 230;  //设置的最大亮度值/*** 判断是否开启了自动亮度调节** @param context* @return*/public static boolean IsAutoBrightness(Context context) {boolean IsAutoBrightness = false;try {IsAutoBrightness = Settings.System.getInt(context.getContentResolver(),Settings.System.SCREEN_BRIGHTNESS_MODE) == Settings.System.SCREEN_BRIGHTNESS_MODE_AUTOMATIC;} catch (Settings.SettingNotFoundException e) {e.printStackTrace();}return IsAutoBrightness;}/*** 获取当前系统屏幕的亮度** @param context* @return*/public static int getScreenBrightness(Context context) {int nowBrightnessValue = 0;ContentResolver resolver = context.getContentResolver();try {nowBrightnessValue = android.provider.Settings.System.getInt(resolver, Settings.System.SCREEN_BRIGHTNESS);} catch (Exception e) {e.printStackTrace();}return nowBrightnessValue;}/*** 设置亮度，程序退出之后亮度失效** @param context* @param brightness*/public static void setCurrentWindowBrightness(Context context, int brightness) {// 如果开启自动亮度，则关闭。否则，设置了亮度值也是无效的if (IsAutoBrightness(context)) {stopAutoBrightness(context);}// context转换为ActivityActivity activity = (Activity) context;WindowManager.LayoutParams lp = activity.getWindow().getAttributes();// 异常处理if (brightness < 1) {brightness = 1;}// 异常处理if (brightness > getBrightnessMax()) {brightness = getBrightnessMax();}if(brightness==MAX_BRIGHTNESS_VALUE){lp.screenBrightness = brightness/255f;}else {lp.screenBrightness = brightness * (1f / getBrightnessMax());}activity.getWindow().setAttributes(lp);}/*** 获取最大亮度* @return max*/private static int getBrightnessMax() {try {Resources system = Resources.getSystem();int resId = system.getIdentifier("config_screenBrightnessSettingMaximum", "integer", "android");if (resId != 0) {return system.getInteger(resId);}}catch (Exception ignore){}return 255;}// 停止自动亮度调节public static void stopAutoBrightness(Context context) {Settings.System.putInt(context.getContentResolver(),Settings.System.SCREEN_BRIGHTNESS_MODE,Settings.System.SCREEN_BRIGHTNESS_MODE_MANUAL);}// 开启亮度自动调节public static void startAutoBrightness(Context context) {Settings.System.putInt(context.getContentResolver(),Settings.System.SCREEN_BRIGHTNESS_MODE,Settings.System.SCREEN_BRIGHTNESS_MODE_AUTOMATIC);}