https://blog.csdn.net/chenlove1/article/details/83627831
    1 继续关系:

    BoxDecoration:实现边框、圆角、阴影、形状、渐变、背景图像
    ShapeDecoration:实现四个边分别指定颜色和宽度、底部线、矩形边色、圆形边色、体育场(竖向椭圆)、 角形(八边角)边色
    FlutterLogoDecoration:实现Flutter图片
    UnderlineTabindicator:下划线
    2 介绍
    一个背景装饰对象,相当于Android中的shape.xml,定制各种各样的背景(边框、圆角、阴影、形状、渐变、背景图像)。
    3 BoxDecoration例子:
    构造方法:
    const BoxDecoration({
    this.color, // 底色
    this.image, // 图片
    this.border, 边色
    this.borderRadius, // 圆角度
    this.boxShadow, // 阴影
    this.gradient, // 渐变
    this.backgroundBlendMode, // 混合Mode
    this.shape = BoxShape.rectangle, // 形状
    })
    3.1 边框+圆角:
    decoration: new BoxDecoration(
    border: new Border.all(color: Color(0xFFFF0000), width: 0.5), // 边色与边宽度
    color: Color(0xFF9E9E9E), // 底色
    // borderRadius: new BorderRadius.circular((20.0)), // 圆角度
    borderRadius: new BorderRadius.vertical(top: Radius.elliptical(20, 50)), // 也可控件一边圆角大小
    ),
    3.2 阴影:
    decoration: new BoxDecoration(
    border: new Border.all(color: Color(0xFFFF0000), width: 0.5), // 边色与边宽度
    // 生成俩层阴影,一层绿,一层黄, 阴影位置由offset决定,阴影模糊层度由blurRadius大小决定(大就更透明更扩散),阴影模糊大小由spreadRadius决定
    boxShadow: [BoxShadow(color: Color(0x99FFFF00), offset: Offset(5.0, 5.0), blurRadius: 10.0, spreadRadius: 2.0), BoxShadow(color: Color(0x9900FF00), offset: Offset(1.0, 1.0)), BoxShadow(color: Color(0xFF0000FF))],
    ),
    3.3 形状(圆形与矩形):
    decoration: new BoxDecoration(
    border: new Border.all(color: Color(0xFFFFFF00), width: 0.5), // 边色与边宽度
    color: Color(0xFF9E9E9E), // 底色
    // shape: BoxShape.circle, // 圆形,使用圆形时不可以使用borderRadius
    shape: BoxShape.rectangle, // 默认值也是矩形
    borderRadius: new BorderRadius.circular((20.0)), // 圆角度
    ),
    3.4 渐变(环形、扫描式、线性):
    decoration: new BoxDecoration(
    border: new Border.all(color: Color(0xFFFFFF00), width: 0.5), // 边色与边宽度
    // 环形渲染
    gradient: RadialGradient(colors: [Color(0xFFFFFF00), Color(0xFF00FF00), Color(0xFF00FFFF)],radius: 1, tileMode: TileMode.mirror)
    //扫描式渐变
    // gradient: SweepGradient(colors: [Color(0xFFFFFF00), Color(0xFF00FF00), Color(0xFF00FFFF)], startAngle: 0.0, endAngle: 1*3.14)
    // 线性渐变
    // gradient: LinearGradient(colors: [Color(0xFFFFFF00), Color(0xFF00FF00), Color(0xFF00FFFF)], begin: FractionalOffset(1, 0), end: FractionalOffset(0, 1))
    ),
    3.4 背景图像:
    decoration: new BoxDecoration(
    border: new Border.all(color: Color(0xFFFFFF00), width: 0.5), // 边色与边宽度
    image: new DecorationImage(
    image: new NetworkImage(‘https://avatar.csdn.net/8/9/A/3_chenlove1.jpg‘), // 网络图片
    // image: new AssetImage(‘graphics/background.png’), 本地图片
    fit: BoxFit.fill // 填满
    // centerSlice: new Rect.fromLTRB(270.0, 180.0, 1360.0, 730.0),// 固定大小
    ),
    ),
    4 ShapeDecoration例子:
    构造方法:
    const ShapeDecoration({
    this.color,
    this.image,
    this.gradient,
    this.shadows,
    @required this.shape,
    })
    除了shape,其他与BoxDecoration一致,shape研究:
    decoration: new ShapeDecoration(
    color: Color(0xFFFF00FF), // 底色
    // 统一四边颜色和宽度
    shape: Border.all(color: Color(0xFF00FFFF),style: BorderStyle.solid,width: 2)
    // 四个边分别指定颜色和宽度, 当只给bottom时与UnderlineInputBorder一致效果
    // shape: Border(top: b, bottom: b, right: b, left: b)
    // 底部线
    // shape: UnderlineInputBorder( borderSide:BorderSide(color: Color(0xFFFFFFFF), style: BorderStyle.solid, width: 2))
    // 矩形边色
    // shape: RoundedRectangleBorder(borderRadius: BorderRadius.all(Radius.circular(10)), side: BorderSide(color: Color(0xFFFFFFFF), style: BorderStyle.solid, width: 2))
    // 圆形边色
    // shape: CircleBorder(side: BorderSide(color: Color(0xFFFFFF00), style: BorderStyle.solid, width: 2))
    // 体育场(竖向椭圆)
    // shape: StadiumBorder(side: BorderSide(width: 2, style: BorderStyle.solid, color: Color(0xFF00FFFF))
    // 角形(八边角)边色
    // shape: BeveledRectangleBorder(borderRadius: BorderRadius.all(Radius.circular(10)), side: BorderSide(color: Color(0xFFFFFFFF), style: BorderStyle.solid, width: 2))
    ),
    5 FlutterLogoDecoration例子:
    构造方法:
    const FlutterLogoDecoration({
    this.lightColor = const Color(0xFF42A5F5), // Colors.blue[400]
    this.darkColor = const Color(0xFF0D47A1), // Colors.blue[900]
    this.textColor = const Color(0xFF616161),
    this.style = FlutterLogoStyle.markOnly,
    this.margin = EdgeInsets.zero,
    })
    这个就不解析了,Flutter的logo,开发没啥用!
    6 UnderlineTabindicator例子:
    构造方法:
    const UnderlineTabIndicator({
    this.borderSide = const BorderSide(width: 2.0, color: Colors.white),
    this.insets = EdgeInsets.zero,
    })
    这个比较简单就是加下划线,可以设置Insets值(控制下划高底,左右边距)
    decoration: new UnderlineTabIndicator(
    borderSide: BorderSide(width: 2.0, color: Colors.white),
    insets: EdgeInsets.fromLTRB(0,0,0,10)
    ),