Flutter之ConstrainedBox组件

/**
 * 限制子元素的最大最小宽高
 * ConstrainedBox({
    Key key,
    @required this.constraints,//限制条件
    Widget child
    })
 */
/**
 *const BoxConstraints({
    this.minWidth = 0.0,
    this.maxWidth = double.infinity,
    this.minHeight = 0.0,
    this.maxHeight = double.infinity
    })
 */