自定义可跟随父Widget弹出显示的弹窗效果。支持自定义事件，默认 转发、收藏、删除。有需要的小伙伴可以直接拿去使用。

效果图

• 实现要点
  • 参考PopMenu实现弹出透明页面，借鉴了https://blog.csdn.net/email_jade/article/details/87922051这位老哥的思想。

class CustomRoute extends PopupRoute {
Widget child;

CustomRoute({@required this.child});

@override
Color get barrierColor => null;
  
@override
bool get barrierDismissible => true;

@override
String get barrierLabel => null;

@override
Widget buildPage(BuildContext context, Animation<double> animation,
Animation<double> secondaryAnimation) {
    return child;
}

@override
Duration get transitionDuration => Duration(milliseconds: 200);
}

• 参考flutter 的toolTip实现弹窗的位置绑定

///参考tooltip的控件绑定
class _PositionDelegate extends SingleChildLayoutDelegate {
_PositionDelegate({
  @required this.target,
  @required this.verticalOffset,
  @required this.preferBelow,
})  : assert(target != null),
      assert(verticalOffset != null),
      assert(preferBelow != null);

 final Offset target;

final double verticalOffset;

final bool preferBelow;

@override
BoxConstraints getConstraintsForChild(BoxConstraints constraints) =>
  constraints.loosen();

@override
Offset getPositionForChild(Size size, Size childSize) {
return positionDependentBox(
  size: size,
  childSize: childSize,
  target: target,
  verticalOffset: verticalOffset,
  preferBelow: preferBelow,
);
}

@override
bool shouldRelayout(_PositionDelegate oldDelegate) {
return target != oldDelegate.target ||
    verticalOffset != oldDelegate.verticalOffset ||
    preferBelow != oldDelegate.preferBelow;
}
}

• 弹窗布局文件（这个完全可以根据自生需求修改）
  CustomSingleChildLayoutl

 ///弹窗 widget
 Widget _buildChild(BuildContext context, double verOffset, bool isPrefer,
 List<Widget> items) {
 final RenderBox box = context.findRenderObject();
 final Offset target = box.localToGlobal(box.size.topCenter(Offset.zero));

 /* 
  *
  *const CustomSingleChildLayout({
    Key key,
    @required this.delegate,//控制子项布局的委托。
    Widget child,
  }) : assert(delegate != null),
       super(key: key, child: child);*/
 return CustomSingleChildLayout(
//位置绑定
 delegate: _PositionDelegate(
    target: target,
    verticalOffset: verOffset ?? 0.0,
    preferBelow: isPrefer ?? false,
 ),
  child: GestureDetector(
    child: Container(
      width: (items == null || items.isEmpty)
          ? 171.0
          : ((items.length) / 2) * 57.0,
      height: 45.0,
       child: Column(
         children: <Widget>[
           Container(
             height: 36.0,
             alignment: Alignment.center,
             decoration: BoxDecoration(
               shape: BoxShape.rectangle,
               color: Color(0xe6060606),
               borderRadius: BorderRadius.circular(5.0),
             ),
             child: Row(
               mainAxisAlignment: MainAxisAlignment.spaceEvenly,
               crossAxisAlignment: CrossAxisAlignment.center,
               children: items ??
                   <Widget>[
                     GestureDetector(
                       child: Text(
                         '转发',
                         style: TextStyle(color: Colors.white),
                       ),
                       onTap: onDefaultForward,
                       onTapCancel: () => Navigator.of(context).pop(),
                     ),
                     Container(
                       width: 0.5,
                       color: Colors.white,
                     ),
                     GestureDetector(
                       onTap: onDefaultCollection,
                       child:
                           Text('收藏', style: TextStyle(color: Colors.white)),
                     ),
                     Container(
                       width: 0.5,
                       color: Colors.white,
                     ),
                     GestureDetector(
                       onTap: onDefaultDelete,
                       child:
                           Text('删除', style: TextStyle(color: Colors.white)),
                     )
                   ],
             ),
           ),
           Image.asset('assets/images/icon_black_arrow_down.png')
         ],
       ),
       ),
     ),
   );
   }
  }

• CustomRoute的使用请参考我的 PopupRoute文章
  完整代码已上传我的 github