C#中的流畅接口和继承 [英] Fluent interfaces and inheritance in C#

问题描述

我会举例说明一个问题.有一个接口流畅的基类:

I'll show a problem by example. There is a base class with fluent interface:

class FluentPerson
{
    private string _FirstName = String.Empty;
    private string _LastName = String.Empty;

    public FluentPerson WithFirstName(string firstName)
    {
        _FirstName = firstName;
        return this;
    }

    public FluentPerson WithLastName(string lastName)
    {
        _LastName = lastName;
        return this;
    }

    public override string ToString()
    {
        return String.Format("First name: {0} last name: {1}", _FirstName, _LastName);
    }
}

和一个子类:

class FluentCustomer : FluentPerson
{
    private long _Id;

    private string _AccountNumber = String.Empty;

    public FluentCustomer WithAccountNumber(string accountNumber)
    {
        _AccountNumber = accountNumber;
        return this;
    }
    public FluentCustomer WithId(long id)
    {
        _Id = id;
        return this;
    }

    public override string ToString()
    {
        return base.ToString() + String.Format(" account number: {0} id: {1}", _AccountNumber, _Id);
    }
}

问题在于，当您调用 customer.WithAccountNumber("000").WithFirstName("John").WithLastName("Smith") 时，您无法添加 .WithId(123) 最终是因为 WithLastName() 方法的返回类型是 FluentPerson(不是 FluentCustomer).

The problem is that when you call customer.WithAccountNumber("000").WithFirstName("John").WithLastName("Smith") you can't add .WithId(123) in the end because return type of the WithLastName() method is FluentPerson (not FluentCustomer).

这个问题通常是如何解决的?

How this problem usually solved?

推荐答案

您可以使用泛型来实现这一点.

You can use generics to achieve that.

public class FluentPerson<T>
    where T : FluentPerson<T>
{
    public T WithFirstName(string firstName)
    {
        // ...
        return (T)this;
    }

    public T WithLastName(string lastName)
    {
        // ...
        return (T)this;
    }
}

public class FluentCustomer : FluentPerson<FluentCustomer>
{
    public FluentCustomer WithAccountNumber(string accountNumber)
    {
        // ...
        return this;
    }
}

现在:

var customer = new FluentCustomer()
  .WithAccountNumber("123")
  .WithFirstName("Abc")
  .WithLastName("Def")
  .ToString();

这篇关于C#中的流畅接口和继承的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！