C# 中面向对象编程的 SOLID 原则

SRP: Splitting a non-SRP class

代码示例

1// 不符合 SRP
2public class RegisterService
3{
4    public void RegisterUser(string username)
5    {
6        if (username == "admin")
7            throw new InvalidOperationException();
8
9        SqlConnection connection = new SqlConnection();
10        connection.Open();
11        SqlCommand command = new SqlCommand("INSERT INTO [...]");//Insert user into database. 
12
13        SmtpClient client = new SmtpClient("smtp.myhost.com");
14        client.Send(new MailMessage()); //Send a welcome email. 
15    }
16}

代码示例

1public void RegisterUser(string username)
2{
3    if (username == "admin")
4        throw new InvalidOperationException();
5
6    _userRepository.Insert(...);
7    
8    _emailService.Send(...);
9}

OCP: Modifying OldClass instead of extending

代码示例

1// 不符合 OCP
2public double Area(object[] shapes)
3{
4    double area = 0;
5    foreach (var shape in shapes)
6    {
7        if (shape is Rectangle)
8        {
9            Rectangle rectangle = (Rectangle) shape;
10            area += rectangle.Width*rectangle.Height;
11        }
12        else
13        {
14            Circle circle = (Circle)shape;
15            area += circle.Radius * circle.Radius * Math.PI;
16        }
17    }
18
19    return area;
20}
21
22public class AreaCalculator
23{
24    public double Area(Rectangle[] shapes)
25    {
26        double area = 0;
27        foreach (var shape in shapes)
28        {
29            area += shape.Width*shape.Height;
30        }
31
32        return area;
33    }
34}

代码示例

1public abstract class Shape
2{
3    public abstract double Area();
4}
5
6public class Rectangle : Shape
7{
8    public double Width { get; set; }
9    public double Height { get; set; }
10    public override double Area()
11    {
12        return Width*Height;
13    }
14}
15
16public class Circle : Shape
17{
18    public double Radius { get; set; }
19    public override double Area()
20    {
21        return Radius*Radius*Math.PI;
22    }
23}
24
25public double Area(Shape[] shapes)
26{
27    double area = 0;
28    foreach (var shape in shapes)
29    {
30        area += shape.Area();
31    }
32
33    return area;
34}

LSP: seamless substitution for the B class in existing code

代码示例

1namespace SOLID_PRINCIPLES.LSP
2{
3    class Program
4    {
5        static void Main(string[] args)
6        {
7            Apple apple = new Orange();
8            Debug.WriteLine(apple.GetColor());
9        }
10    }
11    public class Apple
12    {
13        public virtual string GetColor()
14        {
15            return "Red";
16        }
17    }
18    public class Orange : Apple
19    {
20        public override string GetColor()
21        {
22            return "Orange";
23        }
24    }
25}

代码示例

1namespace SOLID_PRINCIPLES.LSP
2{
3    class Program
4    {
5        static void Main(string[] args)
6        {
7            Fruit fruit = new Orange();
8            Debug.WriteLine(fruit.GetColor());
9            fruit = new Apple();
10            Debug.WriteLine(fruit.GetColor());
11        }
12    }
13    public abstract class Fruit
14    {
15        public abstract string GetColor();
16    }
17    public class Apple : Fruit
18    {
19        public override string GetColor()
20        {
21            return "Red";
22        }
23    }
24    public class Orange : Fruit
25    {
26        public override string GetColor()
27        {
28            return "Orange";
29        }
30    }
31}

ISP: Only inherit applicable methods

代码示例

1// 不符合接口隔离原则  
2  
3  public interface IWorker  
4  {  
5      string ID { get; set; }  
6      string Name { get; set; }  
7      string Email { get; set; }  
8      float MonthlySalary { get; set; }  
9      float OtherBenefits { get; set; }  
10      float HourlyRate { get; set; }  
11      float HoursInMonth { get; set; }  
12      float CalculateNetSalary();  
13      float CalculateWorkedSalary();  
14  }  
15  
16  public class FullTimeEmployee : IWorker  
17  {  
18      public string ID { get; set; }  
19      public string Name { get; set; }  
20      public string Email { get; set; }  
21      public float MonthlySalary { get; set; }  
22      public float OtherBenefits { get; set; }  
23      public float HourlyRate { get; set; }  
24      public float HoursInMonth { get; set; }  
25      public float CalculateNetSalary() => MonthlySalary + OtherBenefits;  
26      public float CalculateWorkedSalary() => throw new NotImplementedException();  
27  }  
28  
29  public class ContractEmployee : IWorker  
30  {  
31      public string ID { get; set; }  
32      public string Name { get; set; }  
33      public string Email { get; set; }  
34      public float MonthlySalary { get; set; }  
35      public float OtherBenefits { get; set; }  
36      public float HourlyRate { get; set; }  
37      public float HoursInMonth { get; set; }  
38      public float CalculateNetSalary() => throw new NotImplementedException();  
39      public float CalculateWorkedSalary() => HourlyRate * HoursInMonth;  
40  }

代码示例

1// 符合接口隔离原则  
2  
3    public interface IBaseWorker  
4    {  
5        string ID { get; set; }  
6        string Name { get; set; }  
7        string Email { get; set; }  
8         
9         
10    }  
11  
12    public interface IFullTimeWorkerSalary : IBaseWorker  
13    {  
14        float MonthlySalary { get; set; }  
15        float OtherBenefits { get; set; }  
16        float CalculateNetSalary();  
17    }  
18  
19    public interface IContractWorkerSalary : IBaseWorker  
20    {  
21        float HourlyRate { get; set; }  
22        float HoursInMonth { get; set; }  
23        float CalculateWorkedSalary();  
24    }  
25  
26    public class FullTimeEmployeeFixed : IFullTimeWorkerSalary  
27    {  
28        public string ID { get; set; }  
29        public string Name { get; set; }  
30        public string Email { get; set; }  
31        public float MonthlySalary { get; set; }  
32        public float OtherBenefits { get; set; }  
33        public float CalculateNetSalary() => MonthlySalary + OtherBenefits;  
34    }  
35  
36    public class ContractEmployeeFixed : IContractWorkerSalary  
37    {  
38        public string ID { get; set; }  
39        public string Name { get; set; }  
40        public string Email { get; set; }  
41        public float HourlyRate { get; set; }  
42        public float HoursInMonth { get; set; }  
43        public float CalculateWorkedSalary() => HourlyRate * HoursInMonth;  
44    }

DIP: Changes to Objects A and B will not affect the other

代码示例

1public interface ICustomerDataAccess
2{
3    string GetCustomerName(int id);
4}

代码示例

1public class CustomerDataAccess: ICustomerDataAccess
2{
3    public CustomerDataAccess() {
4    }
5
6    public string GetCustomerName(int id) {
7        return "Dummy Customer Name";        
8    }
9}

代码示例

1public class DataAccessFactory
2{
3    public static ICustomerDataAccess GetCustomerDataAccessObj() 
4    {
5        return new CustomerDataAccess();
6    }
7}

代码示例

1public class CustomerBusinessLogic
2{
3    ICustomerDataAccess _custDataAccess;
4
5    public CustomerBusinessLogic()
6    {
7        _custDataAccess = DataAccessFactory.GetCustomerDataAccessObj();
8    }
9
10    public string GetCustomerName(int id)
11    {
12        return _custDataAccess.GetCustomerName(id);
13    }
14}

代码示例

1public interface ICustomerDataAccess
2{
3    string GetCustomerName(int id);
4}
5
6public class CustomerDataAccess: ICustomerDataAccess
7{
8    public CustomerDataAccess() {
9    }
10
11    public string GetCustomerName(int id) {
12        return "Dummy Customer Name";        
13    }
14}
15
16public class DataAccessFactory
17{
18    public static ICustomerDataAccess GetCustomerDataAccessObj() 
19    {
20        return new CustomerDataAccess();
21    }
22}
23
24public class CustomerBusinessLogic
25{
26    ICustomerDataAccess _custDataAccess;
27
28    public CustomerBusinessLogic()
29    {
30        _custDataAccess = DataAccessFactory.GetCustomerDataAccessObj();
31    }
32
33    public string GetCustomerName(int id)
34    {
35        return _custDataAccess.GetCustomerName(id);
36    }
37}

Visual chart of our data access program