public void destroy() {
    super.destroy();

    if (this._btnTypeFileShkPem != null) {
      this._btnTypeFileShkPem.removeItemListener(this);
      this._btnTypeFileShkPem.destroy();
      this._btnTypeFileShkPem = null;
    }

    if (this._btnTypeFileShkDer != null) {
      this._btnTypeFileShkDer.removeItemListener(this);
      this._btnTypeFileShkDer.destroy();
      this._btnTypeFileShkDer = null;
    }
  }