使用AnimatedBuilder来包装Container并实现动画效果。

示例代码：

class MyAnimatedContainer extends StatefulWidget {
  @override
  _MyAnimatedContainerState createState() => _MyAnimatedContainerState();
}

class _MyAnimatedContainerState extends State {
  double _width = 100.0;
  double _height = 100.0;

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        AnimatedBuilder(
          animation: _animationController,
          builder: (BuildContext context, Widget child) {
            return Container(
              width: _width,
              height: _height,
              color: Colors.red,
              child: child,
            );
          },
        ),
        FlatButton(
          child: Text('Start Animation'),
          onPressed: () {
            setState(() {
              _width = 200.0;
              _height = 200.0;
            });
          },
        ),
      ],
    );
  }
}

在这个例子中，我们使用AnimatedBuilder来包装一个Container，在点击FlatButton时改变Container的宽度和高度，实现动画效果。记得要在setState中改变宽度和高度，这样AnimatedBuilder才会重新build，产生动画效果。