AspectRatio

是一個widget，將子widget的大小指定為某個特定的寬高比

定義

 const AspectRatio({
    Key key,
    @required this.aspectRatio,
    Widget child
  })

• aspectRatio → double 寬高比

new Container(
      color: Colors.grey,
      alignment: Alignment.center,
      width: 200.0,
      height: 200.0,
      child: new AspectRatio(
        aspectRatio: 2,
        child: new Container(
          color: Colors.red,
        ),
      ),
    )