在C＃中，如何实例化一个方法内传递的泛型类型？ [英] In C#, how to instantiate a passed generic type inside a method?

问题描述

如何在我的 InstantiateType< T> 方法中实例化类型T？

出现错误：'T'是一个'类型参数'，但用作'变量'。：

（SCROLL DOWN FOR REFACTORED ANSWER）

  using System; 
使用System.Collections.Generic; 
使用System.Linq; 
使用System.Text; 
 
名称空间TestGeneric33 
 {
类程序
 {
 static void Main（string [] args）
 {
容器容器= new Container（）; 
 Console.WriteLine（container.InstantiateType< Customer>（Jim，Smith））; 
 Console.WriteLine（container.InstantiateType< Employee>（Joe，Thompson））; 
 Console.ReadLine（）; 
 
 
 
 public class Container 
 {
 public T InstantiateType< T>（string firstName，string lastName）其中T：IPerson 
 {
 T obj = T（）; 
 obj.FirstName（firstName）; 
 obj.LastName（lastName）; 
 return obj; 
} 
 
} 
 
公共接口IPerson 
 {
字符串FirstName {get;组; } 
字符串姓氏{get;组; } 
} 
 
 public class Customer：IPerson 
 {
 public string FirstName {get;组; } 
 public string LastName {get;组; } 
 public string Company {get;组; } 
} 
 
 public class Employee：IPerson 
 {
 public string FirstName {get;组; } 
 public string LastName {get;组; } 
 public int EmployeeNumber {get;组; } 
} 
} 
  

REFACTORED ANSWER：

感谢所有评论，他们让我走上了正轨，这就是我想要做的：

c $ c>使用系统;

名称空间TestGeneric33
{
类程序
{
static void Main（string [] args）
{
容器容器= new Container（）;
Customer customer1 = container.InstantiateType< Customer>（Jim，Smith）;
Employee employee1 = container.InstantiateType< Employee>（Joe，Thompson）;
Console.WriteLine（PersonDisplayer.SimpleDisplay（customer1））;
Console.WriteLine（PersonDisplayer.SimpleDisplay（employee1））;
Console.ReadLine（）;


$ b $ public class Container
{
public T InstantiateType< T>（string firstName，string lastName）其中T：IPerson，new ）
{
T obj = new T（）;
obj.FirstName = firstName;
obj.LastName = lastName;
return obj;
}
}

公共接口IPerson
{
字符串FirstName {get;组; }
字符串姓氏{get;组; }
}

public class PersonDisplayer
{
private IPerson _person;

public PersonDisplayer（IPerson person）
{
_person = person;
}

public string SimpleDisplay（）
{
return String.Format（{1}，{0}，_person.FirstName，_person.LastName） ;


public static string SimpleDisplay（IPerson person）
{
PersonDisplayer personDisplayer = new PersonDisplayer（person）;
return personDisplayer.SimpleDisplay（）;
}
}

public class Customer：IPerson
{
public string FirstName {get;组; }
public string LastName {get;组; }
public string Company {get;组; }
}

public class Employee：IPerson
{
public string FirstName {get;组; }
public string LastName {get;组; }
public int EmployeeNumber {get;组; }
}
}

解决方案

声明你的方法是这样的：
$ b $ pre $ public string InstantiateType< T>（string firstName，string lastName）
where T： IPerson，new（）


注意最后的附加约束。然后在方法体中创建一个 new 实例：

  T obj =新的T（）; 
  

How can I instantiate the type T inside my InstantiateType<T> method below?

I'm getting the error: 'T' is a 'type parameter' but is used like a 'variable'.:

(SCROLL DOWN FOR REFACTORED ANSWER)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace TestGeneric33
{
    class Program
    {
        static void Main(string[] args)
        {
            Container container = new Container();
            Console.WriteLine(container.InstantiateType<Customer>("Jim", "Smith"));
            Console.WriteLine(container.InstantiateType<Employee>("Joe", "Thompson"));
            Console.ReadLine();
        }
    }

    public class Container
    {
        public T InstantiateType<T>(string firstName, string lastName) where T : IPerson
        {
            T obj = T();
            obj.FirstName(firstName);
            obj.LastName(lastName);
            return obj;
        }

    }

    public interface IPerson
    {
        string FirstName { get; set; }
        string LastName { get; set; }
    }

    public class Customer : IPerson
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string Company { get; set; }
    }

    public class Employee : IPerson
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public int EmployeeNumber { get; set; }
    }
}

REFACTORED ANSWER:

Thanks for all the comments, they got me on the right track, this is what I wanted to do:

using System;

namespace TestGeneric33
{
    class Program
    {
        static void Main(string[] args)
        {
            Container container = new Container();
            Customer customer1 = container.InstantiateType<Customer>("Jim", "Smith");
            Employee employee1 = container.InstantiateType<Employee>("Joe", "Thompson");
            Console.WriteLine(PersonDisplayer.SimpleDisplay(customer1));
            Console.WriteLine(PersonDisplayer.SimpleDisplay(employee1));
            Console.ReadLine();
        }
    }

    public class Container
    {
        public T InstantiateType<T>(string firstName, string lastName) where T : IPerson, new()
        {
            T obj = new T();
            obj.FirstName = firstName;
            obj.LastName = lastName;
            return obj;
        }
    }

    public interface IPerson
    {
        string FirstName { get; set; }
        string LastName { get; set; }
    }

    public class PersonDisplayer
    {
        private IPerson _person;

        public PersonDisplayer(IPerson person)
        {
            _person = person;
        }

        public string SimpleDisplay()
        {
            return String.Format("{1}, {0}", _person.FirstName, _person.LastName);
        }

        public static string SimpleDisplay(IPerson person)
        {
            PersonDisplayer personDisplayer = new PersonDisplayer(person);
            return personDisplayer.SimpleDisplay();
        }
    }

    public class Customer : IPerson
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string Company { get; set; }
    }

    public class Employee : IPerson
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public int EmployeeNumber { get; set; }
    }
}

解决方案

Declare your method like this:

public string InstantiateType<T>(string firstName, string lastName) 
              where T : IPerson, new()

Notice the additional constraint at the end. Then create a new instance in the method body:

T obj = new T();    

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