如何在横向模式下将flutter BottomNavigationBar放置在左侧？

class CustomBottomNavigationBar extends StatefulWidget {
  @override
  _CustomBottomNavigationBarState createState() =>
      _CustomBottomNavigationBarState();
}

class _CustomBottomNavigationBarState
    extends State<CustomBottomNavigationBar> {
  int _currentIndex = 0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Stack(
        children: [
          Offstage(
            offstage: _currentIndex != 0,
            child: _buildPage1(),
          ),
          Offstage(
            offstage: _currentIndex != 1,
            child: _buildPage2(),
          ),
          Offstage(
            offstage: _currentIndex != 2,
            child: _buildPage3(),
          ),
        ],
      ),
      bottomNavigationBar: Row(
        children: [
          Expanded(
            child: GestureDetector(
              onTap: () {
                setState(() {
                  _currentIndex = 0;
                });
              },
              child: Container(
                color: _currentIndex == 0 ? Colors.blue : Colors.transparent,
                child: Center(
                  child: Text(
                    'Page 1',
                    style: TextStyle(
                      color: _currentIndex == 0 ? Colors.white : Colors.black,
                    ),
                  ),
                ),
              ),
            ),
          ),
          Expanded(
            child: GestureDetector(
              onTap: () {
                setState(() {
                  _currentIndex = 1;
                });
              },
              child: Container(
                color: _currentIndex == 1 ? Colors.blue : Colors.transparent,
                child: Center(
                  child: Text(
                    'Page 2',
                    style: TextStyle(
                      color: _currentIndex == 1 ? Colors.white : Colors.black,
                    ),
                  ),
                ),
              ),
            ),
          ),
          Expanded(
            child: GestureDetector(
              onTap: () {
                setState(() {
                  _currentIndex = 2;
                });
              },
              child: Container(
                color: _currentIndex == 2 ? Colors.blue : Colors.transparent,
                child: Center(
                  child: Text(
                    'Page 3',
                    style: TextStyle(
                      color: _currentIndex == 2 ? Colors.white : Colors.black,
                    ),
                  ),
                ),
              ),
            ),
          ),
        ],
      ),
    );
  }

  Widget _buildPage1() {
    return Container(
      color: Colors.red,
      child: Center(
        child: Text(
          'Page 1',
          style: TextStyle(
            color: Colors.white,
            fontSize: 24,
          ),
        ),
      ),
    );
  }

  Widget _buildPage2() {
    return Container(
      color: Colors.green,
      child: Center(
        child: Text(
          'Page 2',
          style: TextStyle(
            color: Colors.white,
            fontSize: 24,
          ),
        ),
      ),
    );
  }

  Widget _buildPage3() {
    return Container(
      color: Colors.blue,
      child: Center(
        child: Text(
          'Page 3',
          style: TextStyle(
            color: Colors.white,
            fontSize: 24,
          ),
        ),
      ),
    );
  }
}

class MainPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Flutter BottomNavigationBar'),
      ),
      body: CustomBottomNavigationBar(),
    );
  }
}