Flutter自定义Widget #

class UserCard extends StatelessWidget {
  final String name;
  final String email;
  final String? avatarUrl;
  
  const UserCard({
    required this.name,
    required this.email,
    this.avatarUrl,
  });
  
  @override
  Widget build(BuildContext context) {
    return Card(
      child: Padding(
        padding: EdgeInsets.all(16),
        child: Row(
          children: [
            CircleAvatar(
              backgroundImage: avatarUrl != null 
                  ? NetworkImage(avatarUrl!) 
                  : null,
              child: avatarUrl == null 
                  ? Text(name[0]) 
                  : null,
            ),
            SizedBox(width: 12),
            Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: [
                Text(name, style: TextStyle(fontWeight: FontWeight.bold)),
                Text(email, style: TextStyle(color: Colors.grey)),
              ],
            ),
          ],
        ),
      ),
    );
  }
}

CustomPaint(
  painter: MyPainter(),
  size: Size(200, 200),
)

class MyPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    final paint = Paint()
      ..color = Colors.blue
      ..style = PaintingStyle.fill;
    
    canvas.drawCircle(
      Offset(size.width / 2, size.height / 2),
      size.width / 2,
      paint,
    );
  }
  
  @override
  bool shouldRepaint(MyPainter oldDelegate) => false;
}