C# 从字符串名称实例化一个 Class

Question

有多个 classes 做很多事情，我不得不实例化其中之一，填充一些属性并调用一个方法。示例将具有以下方法，例如

        public class Method100Response201
    {
        public string R1_01 { get; set; }
        public void DoSpecialThing()
        { Console.WriteLine ("Something Blue..}"); }
    }
    public class Method100Response404
    {
        public string R2_01 { get; set; }
        public void DoSpecialThing()
        { Console.WriteLine ("Something Old..}"); }
    }
    public class Method110Response200
    {
        public string R3_01 { get; set; }
        public void DoSpecialThing()
        { Console.WriteLine ("Something New..}"); }
    }

所有这些都在程序 class 中的同一个命名空间中，我有机制找出我需要哪个 Class：

       static void Main(string[] args)
    {
        int[] MethodResponse = DoSomethingHere (23, "something", true);
        string DerivedClassName = ResponseModel(MethodResponse[0], MethodResponse[1]);
        Console.WriteLine (
            "For method " + MethodResponse[0].ToString () 
            + " and response " + MethodResponse[1].ToString ()
            + " you must instantiate Class " 
            + DerivedClassName);
        Console.ReadKey ();

        //how do I do this????
        //const string objectToInstantiate = "MyProject.Domain.MyNewTestClass, MyTestProject";
        //var objectType = Type.GetType (objectToInstantiate);
        //dynamic instantiatedObject = Activator.CreateInstance (objectType) as ITestClass;
        // set a property value
        //instantiatedObject.Name = DerivedClassName;
        // get a property value
        //string name = instantiatedObject.Name;

        // call a method - output "Something Blue.."
        //Console.Write (instantiatedObject.DoSpecialThing ());

    }

    public static int[] DoSomethingHere (int param1, string param2, bool whatever)
    {
        int firstInt = 0; int secondInt = 0;
        //
        //lots of work here, I end up with method and selector.. 
        //
        firstInt = 100;
        secondInt = 201;
        return new int[] { firstInt, secondInt };
    }

    public static string ResponseModel(int method, int response)
    {
        string returnClass = String.Empty;

        switch (method)
            {
            case 100:
                if (response == 201)
                { Console.WriteLine ("Case 100,201"); returnClass = "Method100Response201"; }
                else
                { Console.WriteLine ("Case 100,404"); returnClass = "Method100Response404"; }
                break;
            case 110:
                Console.WriteLine ("Case 100,404"); returnClass = "Method110Response200";
                break;
            case 120:
                // ...
                break;
            }
        return returnClass;
    }

我尝试过一种叫做 Activator 的东西，我不是专家，这对我来说真的很重要。有人可以帮我吗？（基于 SO 中已发布的解决方案，我对我正在尝试的一些代码发表了评论。谢谢）。

Answer 1

这个技术叫做Reflection，意思是从字符串中调用一个实例。我的电话 class 将是

public class Class1
{
    public string Property { get; set; } = "I'm class1";
    public void DoSpecialThings()
    {
        Console.WriteLine("Class1 does special things");
    }
}

接下来我在静态函数中创建一个实例，应该将所有 classes 放在同一个命名空间中以便于控制

    public static dynamic GetClassFromString(string className)
    {
        var classAddress = $"NetCoreScripts.{className}";
        Type type = GetType(classAddress);

        // Check whether the class is existed?
        if (type == null)
            return null;

        // Then create an instance
        object instance = Activator.CreateInstance(type);

        return instance;
    }

还有一个 GetType 方法

    public static Type GetType(string strFullyQualifiedName)
    {
        Type type = Type.GetType(strFullyQualifiedName);
        if (type != null)
            return type;
        foreach (var asm in AppDomain.CurrentDomain.GetAssemblies())
        {
            type = asm.GetType(strFullyQualifiedName);
            if (type != null)
                return type;
        }
        return null;
    }

我用动态类型实现很快，基本上你可以用接口显式编码。

    static async Task Main(string[] args)
    {
        dynamic instance = GetClassFromString("Class1");

        Console.WriteLine(instance.GetType().FullName); //NetCoreScripts.Class1

        Console.WriteLine(instance.GetType().Name); //Class1

        Console.WriteLine(instance.Property); //I'm class1

        instance.Property = "Class1 has been changed";
        Console.WriteLine(instance.Property); //Class1 has been changed

        instance.DoSpecialThings(); // Class1 does special things
    }

Answer 2

您要解决的问题与创建新对象有关。 Here 是一些常用的编码模式。

我想说这是工厂模式的一个很好的用例。我们所做的是将创建对象的责任委托给 factory.

首先，我们可以将它们识别为扩展抽象 class

的 classes

public abstract class MehodResponseBase {
    public abstract void  DoSpecialThing();
    public abstract string responseText;
}

public class Method100Response201 : MehodResponseBase
{
    public override responseText = "Method100Response201";
    public string R1_01 { get; set; }
    public override void DoSpecialThing()
    { Console.WriteLine ("Something Blue..}"); }
}
public class Method100Response404 : MehodResponseBase
{
    public override responseText = "Method100Response404";

    public string R2_01 { get; set; }
    public override void DoSpecialThing()
    { Console.WriteLine ("Something Old..}"); }
}
public class Method110Response200 : MehodResponseBase
{
    public override responseText = "Method110Response200";

    public string R3_01 { get; set; }
    public override void DoSpecialThing()
    { Console.WriteLine ("Something New..}"); }
}

然后我们可以将他们的创建提取到工厂中

pubic class MethodResponseFactory() 
{
    public static MehodResponseBase Make(int method, int response)
    {
        if (method == 100) 
        {
            if(response == 201) 
            {
                return new Method100Response201();
            }

            if(response == 404) 
            {
                return new Method100Response404();
            }
        }

        if (method == 110) 
        {
            if (response == 200) 
            {
                return new Method110Response200();
            }
        }

        throw new MethodResponseCreationException($"Cannot create for mothod: {method} and response: {response}")
    }

}

因此您的响应模型被重构为

public static string ResponseModel(int method, int response)
{
        try 
        {
            return MethodResponseFactory.Make(method, response).returnClass;
        }
        catch (MethodResponseCreationException ex)
        {
            return string.Empty;
        }
}

因此，如您所见，创建对象的所有委托现在都在工厂中。而 resonseModel class 只是调用工厂在 method 和 response.

的基础上构建一个 class

C# 从字符串名称实例化一个 Class

C# Instantiate a Class from String name

c#

static-methods

activator

dynamicobject