android 调节屏幕亮度

public void setBrightness(int level) {
ContentResolver cr = getContentResolver();
Settings.System.putInt(cr, "screen_brightness", level);
Window window = getWindow();
LayoutParams attributes = window.getAttributes();
float flevel = level;
attributes.screenBrightness = flevel / 255;
getWindow().setAttributes(attributes);
}