android 6.0获取 WRITE_SETTINGS 权限

android 6.0上只写在AndroidManifest中是不行的，还必须手动打开才行

    private void setBrightnessMode(Context context, int mode) {
        try {
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
                if (Settings.System.canWrite(context)) {
                    Settings.System.putInt(context.getContentResolver(), Settings.System.SCREEN_BRIGHTNESS_MODE, mode);
                } else {
                    Intent intent = new Intent(android.provider.Settings.ACTION_MANAGE_WRITE_SETTINGS);
                    intent.setData(Uri.parse("package:" + context.getPackageName()));
                    intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                    context.startActivity(intent);
                }
            } else {
                Settings.System.putInt(context.getContentResolver(), Settings.System.SCREEN_BRIGHTNESS_MODE, mode);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }