如何在.NET Core中发出类型

Question

在C#中,如何在运行时使用.NET Core发出新的Type？我可以在.NET 6中找到的所有示例似乎都不适用于.NET内核(它们都是从获取当前AppDomain开始的,而后者在.NET内核中不再存在).

如果可能的话,我将会感谢一个涉及创建Type并向Type添加属性的示例.

Answer 1

这是关于在.NET 4中创建动态类型的帖子.

如何在C#中动态创建一个类？

在接受的答案中只是一个用途AppDomain.

AssemblyBuilder assemblyBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(an, AssemblyBuilderAccess.Run);

这是关于DefineDynamicAssembly在.NET核心中替换功能的另一篇SO帖子.

在.NET Core中是否有任何AssemblyBuilder.DefineDynamicAssembly的替换？

这里是:

AssemblyBuilder.DefineDynamicAssembly(new AssemblyName(Guid.NewGuid().ToString()),AssemblyBuilderAccess.Run);

在"System.Reflection.Emit": "4.0.1"nuget.

另外,有区别TypeBuilder.CreateType功能不再存在,而是创建我们应该使用的类型CreateTypeInfo.是的,它再次来自SO帖子.

TypeBuilder中缺少CreateType.如何移植这个？

这是一个工作修改示例(对于.NET核心),用于创建Type并向Type添加属性.

using System;
using System.Collections.Generic;
using System.Reflection.Emit;
using System.Reflection;

namespace ConsoleApp1
{
    public class FieldDescriptor
    {
        public FieldDescriptor(string fieldName, Type fieldType)
        {
            FieldName = fieldName;
            FieldType = fieldType;
        }
        public string FieldName { get; }
        public Type FieldType { get;  }
    }

    public static class MyTypeBuilder
    {
        public static object CreateNewObject()
        {
            var myTypeInfo = CompileResultTypeInfo();
            var myType = myTypeInfo.AsType();
            var myObject = Activator.CreateInstance(myType);

            return myObject;
        }

        public static TypeInfo CompileResultTypeInfo()
        {
            TypeBuilder tb = GetTypeBuilder();
            ConstructorBuilder constructor = tb.DefineDefaultConstructor(MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.RTSpecialName);

            var yourListOfFields = new List<FieldDescriptor>()
            {
                new FieldDescriptor("YourProp1",typeof(string)),
                new FieldDescriptor("YourProp2", typeof(int))
            };
            foreach (var field in yourListOfFields)
                CreateProperty(tb, field.FieldName, field.FieldType);

            TypeInfo objectTypeInfo = tb.CreateTypeInfo();
            return objectTypeInfo;
        }

        private static TypeBuilder GetTypeBuilder()
        {
            var typeSignature = "MyDynamicType";
            var an = new AssemblyName(typeSignature);
            var assemblyBuilder = AssemblyBuilder.DefineDynamicAssembly(new AssemblyName(Guid.NewGuid().ToString()), AssemblyBuilderAccess.Run);
            ModuleBuilder moduleBuilder = assemblyBuilder.DefineDynamicModule("MainModule");
            TypeBuilder tb = moduleBuilder.DefineType(typeSignature,
                    TypeAttributes.Public |
                    TypeAttributes.Class |
                    TypeAttributes.AutoClass |
                    TypeAttributes.AnsiClass |
                    TypeAttributes.BeforeFieldInit |
                    TypeAttributes.AutoLayout,
                    null);
            return tb;
        }

        private static void CreateProperty(TypeBuilder tb, string propertyName, Type propertyType)
        {
            FieldBuilder fieldBuilder = tb.DefineField("_" + propertyName, propertyType, FieldAttributes.Private);

            PropertyBuilder propertyBuilder = tb.DefineProperty(propertyName, PropertyAttributes.HasDefault, propertyType, null);
            MethodBuilder getPropMthdBldr = tb.DefineMethod("get_" + propertyName, MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.HideBySig, propertyType, Type.EmptyTypes);
            ILGenerator getIl = getPropMthdBldr.GetILGenerator();

            getIl.Emit(OpCodes.Ldarg_0);
            getIl.Emit(OpCodes.Ldfld, fieldBuilder);
            getIl.Emit(OpCodes.Ret);

            MethodBuilder setPropMthdBldr =
                tb.DefineMethod("set_" + propertyName,
                  MethodAttributes.Public |
                  MethodAttributes.SpecialName |
                  MethodAttributes.HideBySig,
                  null, new[] { propertyType });

            ILGenerator setIl = setPropMthdBldr.GetILGenerator();
            Label modifyProperty = setIl.DefineLabel();
            Label exitSet = setIl.DefineLabel();

            setIl.MarkLabel(modifyProperty);
            setIl.Emit(OpCodes.Ldarg_0);
            setIl.Emit(OpCodes.Ldarg_1);
            setIl.Emit(OpCodes.Stfld, fieldBuilder);

            setIl.Emit(OpCodes.Nop);
            setIl.MarkLabel(exitSet);
            setIl.Emit(OpCodes.Ret);

            propertyBuilder.SetGetMethod(getPropMthdBldr);
            propertyBuilder.SetSetMethod(setPropMthdBldr);
        }
    }
}