How to create this curves in flutter?

Question

How Can I create this curves and two coloured top "appBar" using Flutter?

Answer 1

The CustomPaint widget will do the trick. With it, it's possible to paint custom shapes in the background like the one you asked for. It's just a matter of using the Stack widget to paint the background first and then the other widgets above it.

This is a prototype of the login screen:

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

const loginMainColor = Color.fromARGB(255, 67, 123, 122);
const loginOtherColor = Color.fromARGB(255, 253, 236, 229);

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Custom Shape Widget Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const LoginPage(),
    );
  }
}

class LoginPage extends StatelessWidget {
  const LoginPage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final width = MediaQuery.of(context).size.width;
    final height = MediaQuery.of(context).size.height;
    return Scaffold(
      appBar: AppBar(
        elevation: 0,
        backgroundColor: loginMainColor,
      ),
      backgroundColor: Colors.white,
      body: Stack(
        children: [
          Stack(
            children: [
              CustomPaint(
                size: Size(width, height),
                painter: const BackgroundPainter(90),
              ),
              Padding(
                padding: const EdgeInsets.only(left: 16, right: 16),
                child: Column(
                  mainAxisAlignment: MainAxisAlignment.start,
                  crossAxisAlignment: CrossAxisAlignment.start,
                  children: const [
                    Text(
                      'Log in',
                      style: TextStyle(
                          fontSize: 30,
                          fontWeight: FontWeight.bold,
                          color: Colors.white),
                    ),
                    Padding(
                      padding: EdgeInsets.only(bottom: 60 - 16),
                      child: Text(
                        'Lorem ipsum dolor sit amet',
                        style: TextStyle(
                            fontSize: 16,
                            fontWeight: FontWeight.bold,
                            color: Colors.white),
                      ),
                    ),
                    Padding(
                      padding: EdgeInsets.only(bottom: 30),
                      child: TextField(
                        decoration: InputDecoration(
                          label: Text('Email'),
                          floatingLabelBehavior: FloatingLabelBehavior.always,
                        ),
                      ),
                    ),
                    TextField(
                      decoration: InputDecoration(
                        label: Text('Password'),
                        floatingLabelBehavior: FloatingLabelBehavior.always,
                      ),
                    )
                  ],
                ),
              ),
            ],
          ),
        ],
      ),
    );
  }
}

class BackgroundPainter extends CustomPainter {
  final double titleBarHeight;
  const BackgroundPainter(this.titleBarHeight);

  @override
  void paint(Canvas canvas, Size size) {
    var paint = Paint()..color = loginMainColor;

    const smallRadius = 50.0;
    const bigRadius = 120.0;

    canvas.drawCircle(
        Offset(smallRadius, titleBarHeight - smallRadius), smallRadius, paint);
    canvas.drawRect(
      Rect.fromPoints(
        Offset(0, 0),
        Offset(size.width, titleBarHeight - smallRadius),
      ),
      paint,
    );
    canvas.drawRect(
      Rect.fromPoints(
        Offset(smallRadius, titleBarHeight - smallRadius),
        Offset(size.width, titleBarHeight),
      ),
      paint,
    );

    paint.color = loginOtherColor;
    canvas.drawCircle(
        Offset(size.width, titleBarHeight + 60), bigRadius, paint);

    paint.color = Colors.white;
    canvas.drawCircle(
        Offset(size.width - smallRadius, titleBarHeight + smallRadius),
        smallRadius,
        paint);
    canvas.drawRect(
        Rect.fromPoints(
          Offset(size.width - bigRadius, titleBarHeight),
          Offset(size.width - smallRadius, titleBarHeight + 60 + bigRadius),
        ),
        paint);
    canvas.drawRect(
        Rect.fromPoints(
          Offset(size.width - smallRadius, titleBarHeight + smallRadius),
          Offset(size.width, titleBarHeight + 60 + bigRadius),
        ),
        paint);
  }

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