使用 Reflection.Emit 调用 AutoGenerated 类的方法

Question

您好，我想知道如何在不使用反射的情况下调用尚未存在的类的方法。如您所见，我正在使用生成器类 Weaver（使用 Reflection.Emit）返回一个Func<object>（我无法指定动态类型）。当我检索实例时，我将如何调用它的方法之一，特别是DoInt？

我想要自动生成

class Gen {
            public Gen() {

            }
            public int DoInt(int a,string b) {
               int rez=a+b.count();
                return 3;
            }
        }

生成器类

class Weaver {

            public static Func<object> Weave() {
                var weaver = new Weaver();
                weaver.Run();
                return weaver.output as Func<object>;

            }


            private AssemblyBuilder assemblyBuilder;
            private ModuleBuilder moduleBuilder;
            private TypeBuilder typebuilder;

            private object output;
            public Weaver() {

            }


            private void Run() {
                this.DefineAssembly();
                this.DefineModule();
                this.DefineClass();
                this.DefineMethod();
                this.Wrap();
            }


            private void DefineAssembly() {
                AssemblyName name = new AssemblyName("Coda");
                AppDomain domain = AppDomain.CurrentDomain;
                assemblyBuilder = AssemblyBuilder.DefineDynamicAssembly(name, AssemblyBuilderAccess.RunAndCollect);
            }

            private void DefineModule() {
                this.moduleBuilder = assemblyBuilder.DefineDynamicModule(assemblyBuilder.FullName + ".dll");
            }
            private void DefineClass() {
                this.typebuilder = this.moduleBuilder.DefineType("A", 
                    TypeAttributes.Abstract|TypeAttributes.Public|TypeAttributes.BeforeFieldInit|TypeAttributes.AnsiClass|TypeAttributes.AutoClass,
                    typeof(object), null );
            }
            private void DefineMethod() {
                MethodBuilder methodBuilder = this.typebuilder.DefineMethod("DoInt", MethodAttributes.Public, typeof(int), new[] { typeof(int), typeof(string) });
                var il = methodBuilder.GetILGenerator();
                il.Emit(OpCodes.Ldarg_1);
                il.EmitCall(OpCodes.Call, typeof(Enumerable).GetMethod("Count", BindingFlags.Static), null);
                il.Emit(OpCodes.Ldarg_1);
                il.Emit(OpCodes.Add);
                il.Emit(OpCodes.Ret);
            }

            private void Wrap() {
                Type type = typebuilder.CreateType();
                this.output = Activator.CreateInstance(type);
            }

        }

主要

static void Main(string[] args)
        {
            string t = "astada";
            var c = Weaver.Weave();
            var result=c.GetType().GetMethod("DoInt").Invoke(null, new object[] { 3, "mystring" });  //should be 3+ "mystring".Count() 
            Console.ReadLine();
        }

Answer 1

要使其正常工作，您首先需要修复您的Weaver，因为它包含几个错误：

private void DefineClass()
{
    // TypeAttributes.Abstract should not be used here as we want to create
    // type that can be instantiated
    this.typebuilder = this.moduleBuilder.DefineType(
        "A",
        TypeAttributes.Public | TypeAttributes.BeforeFieldInit | TypeAttributes.AnsiClass | TypeAttributes.AutoClass,
        typeof(object),
        null);
}

private void DefineMethod()
{
    MethodBuilder methodBuilder = this.typebuilder.DefineMethod(
        "DoInt",
        MethodAttributes.Public,
        typeof(int), new[] { typeof(int), typeof(string) });

    var il = methodBuilder.GetILGenerator();

    // Arguments are counted from zero. For instance methods, argument0 is
    // reserved for 'this' instance. So to get "string" argument (second "real" argument),
    // you need Ldarg_2
    il.Emit(OpCodes.Ldarg_2);

    // You cannot get MethodInfo for "Count" method with simple GetMethod(),
    // since it is generic method with several overloads.
    var countMethodInfo = typeof(Enumerable)
        .GetMethods(BindingFlags.Public | BindingFlags.Static)
        .Where(m => m.Name == "Count")
        .Where(m => m.GetParameters().Length == 1)
        .Single()
        //We want Count<char>() method, because we want to count characters on string (casted to IEnumerable<char>).
        .MakeGenericMethod(typeof(char));
    il.EmitCall(OpCodes.Call, countMethodInfo, null);
    il.Emit(OpCodes.Ldarg_1);
    il.Emit(OpCodes.Add);
    il.Emit(OpCodes.Ret);
}

public static object Weave()
{
    var weaver = new Weaver();
    weaver.Run();
    // return weaver.output as Func<object>;
    // Output is an instance of an (dynamically generated) 'A' class, not a Func<>
    return weaver.output;
}

现在有几种方法可以调用 A.DoInt：

1. 反思：

   var c = Weaver.Weave();
   var result = (int)c.GetType().GetMethod("DoInt").Invoke(c, new Object[] { 3, "foo" });
   

2. 创建委托：

   var c = Weaver.Weave();
   var mi = c.GetType().GetMethod("DoInt");
   var del = (Func<int, string, int>)Delegate.CreateDelegate(typeof(Func<int, string, int>), c, mi);
   var result = del(3, "foo");
   

3. 动态：

   var d = Weaver.Weave() as dynamic;
   var result = (int)d.DoInt(3, "foo");
   

4. 界面：

   这是最难做到的。首先你必须声明接口，例如：

   public interface IDoInt
   {
       int DoInt(int i, string s);
   }
   

   您需要在另一个程序集中声明此接口，否则您将无法从动态定义的程序集中使用此类型（由于循环引用）。

   那你需要稍微修改一下Weaver，让你的A类型实现这个接口：

   private void DefineClass()
   {
       this.typebuilder = this.moduleBuilder.DefineType(
           "A",
           TypeAttributes.Public | TypeAttributes.BeforeFieldInit | TypeAttributes.AnsiClass | TypeAttributes.AutoClass,
           typeof(object),
           new[] { typeof(IDoInt) });
   }
   
   private void DefineMethod()
   {
       MethodBuilder methodBuilder = this.typebuilder.DefineMethod(
           "DoInt",
           MethodAttributes.Public | MethodAttributes.HideBySig |
           MethodAttributes.NewSlot |  MethodAttributes.Virtual |
           MethodAttributes.Final,
           typeof(int), new[] { typeof(int), typeof(string) });
   
       // ... rest ot the method is the same ...
   
       // just add this at the end of the method to implement the IDoInt interface
       this.typebuilder.DefineMethodOverride(methodBuilder, typeof(IDoInt).GetMethod("DoInt"));
   }
   

   现在你可以在IDoInt接口上调用DoInt了：

   var i = Weaver.Weave() as IDoInt;
   var result = i.DoInt(3, "foo");