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);   }