flutter - 子 customPaint 无法点击

Question

  GestureDetector(
   // behavior:HitTestBehavior(),
    onTap: (){
      print('hello word');
      //print(gl);
     // print(value.localPosition.dx);
    },
    child:
     CustomPaint(
       size: Size(setRawSize(600), setRawSize(290)),
       foregroundPainter: FunnelPlotCustomPainter(
         viewService.context,
         color: Colors.blue,
         funnelPoltData: fd
        ),
     ),
  ),

我用画布画了一个漏斗图，但我不能点击它。我很困惑。