flutter控件从上到下居中排列

Column(
          children: <Widget>[
            Expanded(child:
            Image.asset('assets/images/$imageName.png')
            ),
            
            Text(
              this.model.title,
              style: TextStyle(
                fontSize: 15,
                color: Colors.white,
              ),
            ),
          ],
        ),

注解：

• column是一个垂直的容器，子控件放在children里面
• 要想让图片居中，需要放在expanded容器里面,官方定义：expanded is a widget that expands a child of a row,column,or flex so that the child fills the available space.
•