Flutter add shadow in Custom painter

Question

I am following some tutorial and fine a very good navbar but issue is when i replace it in my app i need to add shadow.

Here is the code

class BottomNavBarV2 extends StatefulWidget {
  @override
  _BottomNavBarV2State createState() => _BottomNavBarV2State();
}

class _BottomNavBarV2State extends State<BottomNavBarV2> {
  int currentIndex = 0;

  setBottomBarIndex(index) {
    setState(() {
      currentIndex = index;
    });
  }

  @override
  Widget build(BuildContext context) {
    final Size size = MediaQuery.of(context).size;
    return Scaffold(
      backgroundColor: Colors.white.withAlpha(55),
      body: Stack(
        children: [
          Positioned(
            bottom: 0,
            left: 0,
            child: Container(
              width: size.width,
              height: 80,
              child: Stack(
                overflow: Overflow.visible,
                children: [
                  CustomPaint(
                    size: Size(size.width, 80),
                    painter: BNBCustomPainter(),
                  ),
                  Center(
                    heightFactor: 0.6,
                    child: FloatingActionButton(backgroundColor: Colors.orange, child: Icon(Icons.shopping_basket), elevation: 0.1, onPressed: () {}),
                  ),
                  Container(
                    width: size.width,
                    height: 80,
                    child: Row(
                      mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                      children: [
                        IconButton(
                          icon: Icon(
                            Icons.home,
                            color: currentIndex == 0 ? Colors.orange : Colors.grey.shade400,
                          ),
                          onPressed: () {
                            setBottomBarIndex(0);
                          },
                          splashColor: Colors.white,
                        ),
                        IconButton(
                            icon: Icon(
                              Icons.restaurant_menu,
                              color: currentIndex == 1 ? Colors.orange : Colors.grey.shade400,
                            ),
                            onPressed: () {
                              setBottomBarIndex(1);
                            }),
                        Container(
                          width: size.width * 0.20,
                        ),
                        IconButton(
                            icon: Icon(
                              Icons.bookmark,
                              color: currentIndex == 2 ? Colors.orange : Colors.grey.shade400,
                            ),
                            onPressed: () {
                              setBottomBarIndex(2);
                            }),
                        IconButton(
                            icon: Icon(
                              Icons.notifications,
                              color: currentIndex == 3 ? Colors.orange : Colors.grey.shade400,
                            ),
                            onPressed: () {
                              setBottomBarIndex(3);
                            }),
                      ],
                    ),
                  )
                ],
              ),
            ),
          )
        ],
      ),
    );
  }
}

class BNBCustomPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    Paint paint = new Paint()
      ..color = Colors.white
      ..style = PaintingStyle.fill;

    Path path = Path();
    path.moveTo(0, 20); // Start
    path.quadraticBezierTo(size.width * 0.20, 0, size.width * 0.35, 0);
    path.quadraticBezierTo(size.width * 0.40, 0, size.width * 0.40, 20);
    path.arcToPoint(Offset(size.width * 0.60, 20), radius: Radius.circular(20.0), clockwise: false);
    path.quadraticBezierTo(size.width * 0.60, 0, size.width * 0.65, 0);
    path.quadraticBezierTo(size.width * 0.80, 0, size.width, 20);
    path.lineTo(size.width, size.height);
    path.lineTo(0, size.height);
    path.lineTo(0, 20);
    canvas.drawShadow(path, Colors.black, 5, true);
    canvas.drawPath(path, paint);
  }

  @override
  bool shouldRepaint(CustomPainter oldDelegate) {
    return false;
  }
}

Screen shot

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I need to add shadow in this curved navbar. Because body and navbar both is white and navbar curved is not much visible. Need to add little shadow so can see curves easily

Answer 1

You can use the below code to gain the custom shadow for your widget. Just wrap your widget with the below container.

return Container(
  margin: EdgeInsets.only(left: 20, top: 50, right: 20, bottom: 50),
  decoration: BoxDecoration(
    color: Colors.white,
    borderRadius: BorderRadius.only(
      topLeft: Radius.circular(10),
        topRight: Radius.circular(10),
        bottomLeft: Radius.circular(10),
        bottomRight: Radius.circular(10)
    ),
    boxShadow: [
      BoxShadow(
        color: Colors.grey.withOpacity(0.4),
        spreadRadius: 8,
        blurRadius: 10,
        offset: Offset(0, 5), // changes position of shadow
      ),
    ],
  ),
)