c# 以类名为参创建父类相同的类的实例代码

要想创建一个父类相同的类的实例，需要使用 c# 的反射机制。首先需要获取要创建类的 Type 对象，然后使用 Activator.CreateInstance 方法创建实例。

步骤如下：

1. 获取父类的 Type 对象；

Type baseType = typeof(BaseClass);

1. 使用 Type 对象动态创建子类的 Type 对象；

Type subType = TypeBuilder
                .GetTypeBuilder("SubClass")
                .CreateType();

1. 使用 Activator.CreateInstance 方法创建子类的实例；

object instance = Activator.CreateInstance(subType);

完整代码示例：

using System;
using System.Reflection;
using System.Reflection.Emit;

public class BaseClass
{
    public void Print()
    {
        Console.WriteLine("This is base class.");
    }
}

class Program
{
    static void Main(string[] args)
    {
        Type baseType = typeof(BaseClass);

        TypeBuilder subTypeBuilder = GetTypeBuilder("SubClass");
        subTypeBuilder.SetParent(baseType);
        subTypeBuilder.DefineDefaultConstructor(MethodAttributes.Public);

        Type subType = subTypeBuilder.CreateType();

        object instance = Activator.CreateInstance(subType);
        BaseClass baseInstance = instance as BaseClass;
        baseInstance.Print();
    }

    private static TypeBuilder GetTypeBuilder(string className)
    {
        var assemblyName = new AssemblyName(className);
        AssemblyBuilder assemblyBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(assemblyName, AssemblyBuilderAccess.Run);
        ModuleBuilder moduleBuilder = assemblyBuilder.DefineDynamicModule("MainModule");

        TypeBuilder typeBuilder = moduleBuilder.DefineType(
            className,
            TypeAttributes.Public |
            TypeAttributes.Class |
            TypeAttributes.AutoClass |
            TypeAttributes.AnsiClass |
            TypeAttributes.BeforeFieldInit |
            TypeAttributes.AutoLayout,
            null
        );

        return typeBuilder;
    }
}

在上面的示例中，我们建立了一个名为 SubClass 的动态子类，并将它的父类设为了 BaseClass，并创建了它的实例。执行结果：

This is base class.

示例2：

如果子类的构造函数需要传递参数，还需要使用 CreateInstance 方法的重载函数来传入参数。

完整代码示例

using System;
using System.Reflection;
using System.Reflection.Emit;

public class BaseClass
{
    private readonly string message;

    public BaseClass(string message)
    {
        this.message = message;
    }

    public void Print()
    {
        Console.WriteLine(message);
    }
}

class Program
{
    static void Main(string[] args)
    {
        Type baseType = typeof(BaseClass);

        TypeBuilder subTypeBuilder = GetTypeBuilder("SubClass");
        ConstructorBuilder constructorBuilder = DefineConstructor(subTypeBuilder);
        Type subType = subTypeBuilder.CreateType();

        object[] constructorArgs = new object[] { "This is sub class." };
        object instance = Activator.CreateInstance(subType, constructorArgs);
        BaseClass baseInstance = instance as BaseClass;
        baseInstance.Print();
    }

    private static TypeBuilder GetTypeBuilder(string className)
    {
        var assemblyName = new AssemblyName(className);
        AssemblyBuilder assemblyBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(assemblyName, AssemblyBuilderAccess.Run);
        ModuleBuilder moduleBuilder = assemblyBuilder.DefineDynamicModule("MainModule");

        TypeBuilder typeBuilder = moduleBuilder.DefineType(
            className,
            TypeAttributes.Public |
            TypeAttributes.Class |
            TypeAttributes.AutoClass |
            TypeAttributes.AnsiClass |
            TypeAttributes.BeforeFieldInit |
            TypeAttributes.AutoLayout,
            typeof(BaseClass)
        );

        return typeBuilder;
    }

    private static ConstructorBuilder DefineConstructor(TypeBuilder typeBuilder)
    {
        ConstructorBuilder constructorBuilder = typeBuilder.DefineConstructor(
            MethodAttributes.Public,
            CallingConventions.Standard,
            new Type[] { typeof(string) }
        );

        ILGenerator ilGenerator = constructorBuilder.GetILGenerator();
        ilGenerator.Emit(OpCodes.Ldarg_0);
        ilGenerator.Emit(OpCodes.Ldarg_1);
        ilGenerator.Emit(OpCodes.Call, typeof(BaseClass).GetConstructor(new Type[] { typeof(string) }));
        ilGenerator.Emit(OpCodes.Ret);

        return constructorBuilder;
    }
}

在上面的示例中，我们建立了一个名为 SubClass 的动态子类，并将它的父类设为了 BaseClass，SubClass 继承了父类的构造函数，并创建了它的实例。执行结果：

This is sub class.