发出对 lambda 表达式的调用

Question

当我尝试调用 lambda 表达式时出现异常。 lambda 生成一个私有静态方法似乎是真实的。我怎样才能实现我想要的？

    static void Main(string[] args)
    {
        var typeBuilder = CreateTypeBuilder();
        AddStaticMethodAsAProperty(typeBuilder, "StaticPublic", Return1);
        AddStaticMethodAsAProperty(typeBuilder, "StaticPrivate", Return2);
        AddStaticMethodAsAProperty(typeBuilder, "Lambda", () => 3);

        var newType = typeBuilder.CreateType();
        dynamic newObject = Activator.CreateInstance(newType);
        var resultFromStatic = newObject.StaticPublic; //Ok
        var resultFromStaticPrivate = newObject.StaticPrivate; //Additional information: Attempt by method 'NewType.get_StaticPrivate()' to access method 'Test.Program.Return2()' failed.
        var resultFromLambda = newObject.Lambda; //failed with Additional information: Attempt by method 'NewType.get_Lambda()' to access method 'Test.Program.<Main>b__3()' failed.
    }

    public static void AddStaticMethodAsAProperty(TypeBuilder typeBuilder, string propertyName, Func<int> methodToAdd)
    {
        var propertyType = methodToAdd.Method.ReturnType;

        var getPropertyMethodBuilder = typeBuilder.DefineMethod(string.Format("get_{0}", propertyName), MethodAttributes.Public | MethodAttributes.HideBySig, propertyType, Type.EmptyTypes);

        var getIL = getPropertyMethodBuilder.GetILGenerator();

        getIL.Emit(OpCodes.Call, methodToAdd.Method);
        getIL.Emit(OpCodes.Ret);

        var propertyBuilder = typeBuilder.DefineProperty(propertyName, PropertyAttributes.None, propertyType, new Type[] { });
        propertyBuilder.SetGetMethod(getPropertyMethodBuilder);
    }

    public static int Return1()
    {
        return 1;
    }

    private static int Return2()
    {
        return 1;
    }

    private static TypeBuilder CreateTypeBuilder()
    {
        var newTypeName = "NewType";
        var newAssemblyName = new AssemblyName(newTypeName);
        var assemblyBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(newAssemblyName, AssemblyBuilderAccess.Run);
        var moduleBuilder = assemblyBuilder.DefineDynamicModule("MainModule");
        var typeBuilder = moduleBuilder.DefineType(newTypeName
                                            , TypeAttributes.Public |
                                            TypeAttributes.Class |
                                            TypeAttributes.AutoClass |
                                            TypeAttributes.AnsiClass |
                                            TypeAttributes.BeforeFieldInit |
                                            TypeAttributes.AutoLayout
                                            , null);
        return typeBuilder;
    }

Answer 1

methodToAdd 是代表。您正在尝试调用它内部包含的 Method ，但这是错误的方法。您想改为执行委托，这有点复杂。

基本上，您需要在 methodToAdd 上调用 Invoke 方法。这也意味着您需要将委托放在最终代码可访问的地方。换句话说，您需要做很多 C# 编译器通常做的工作——创建包含对委托的引用的匿名类。对该引用调用 callvirt Func<int>.Invoke 是比较简单的部分。

值得庆幸的是，新的 Expression 东西非常棒。所以你应该能够做到这一点：

Expression<Func<T>> expr = () => methodToAdd();
expr.CompileToMethod(getPropertyMethodBuilder);

始终尽量远离发射 IL - 即使 ilasm 本身也在做很多 ILGenerator 没有做的工作。但它仍然必须生成有效的 IL - 并且 call 在错误范围内的私有方法上肯定不是有效的 IL。

Answer 2

我找到了我想做的事情，想法是跟踪函数作为字段，然后在 getter 中调用这个字段。

  static void Main(string[] args)
    {
        var typeBuilder = CreateTypeBuilder();
        AddStaticMethodAsAProperty(typeBuilder, "StaticPublic", Return1);
        AddStaticMethodAsAProperty(typeBuilder, "StaticPrivate", Return2);
        AddStaticMethodAsAProperty(typeBuilder, "Lambda", () => 3);

        var newType = typeBuilder.CreateType();

        dynamic newObject = Activator.CreateInstance(newType);
        foreach (var onNewObjectCreated in _onNewObjectCreated)
        {
            onNewObjectCreated(newObject);
        }

        var resultFromStatic = newObject.StaticPublic; //Ok 1
        var resultFromStaticPrivate = newObject.StaticPrivate; //Ok 2
        var resultFromLambda = newObject.Lambda; //Ok 3
    }

    private static List<Action<object>> _onNewObjectCreated = new List<Action<object>>();
    public static void AddStaticMethodAsAProperty<T>(TypeBuilder typeBuilder, string propertyName, Func<T> valueGetter)
    {
        var propertyType = valueGetter.Method.ReturnType;
        var delegateFieldBuilder = typeBuilder.DefineField(string.Format("_backingDelegate{0}", propertyName), valueGetter.GetType(), FieldAttributes.Private);

        var getMethod = typeBuilder.DefineMethod(string.Format("get_{0}", propertyName), MethodAttributes.Public | MethodAttributes.HideBySig, propertyType, Type.EmptyTypes);


        Action<object> setDelegateFieldAction = newlyCreatedObject => { newlyCreatedObject.GetType().GetField(delegateFieldBuilder.Name, BindingFlags.NonPublic | BindingFlags.Instance).SetValue(newlyCreatedObject, valueGetter); };
        _onNewObjectCreated.Add(setDelegateFieldAction);

        var il = getMethod.GetILGenerator();
        il.Emit(OpCodes.Ldarg_0);//stack [this]
        il.Emit(OpCodes.Ldfld, delegateFieldBuilder);//stack [this._backingDelegateXXX]
        il.Emit(OpCodes.Callvirt, valueGetter.GetType().GetMethod("Invoke"));//stack [valueReturnedByTheDelegate]
        il.Emit(OpCodes.Ret);
        var propertyBuilder = typeBuilder.DefineProperty(propertyName, PropertyAttributes.None, propertyType, new Type[] { });
        propertyBuilder.SetGetMethod(getMethod);
    }

    public static int Return1()
    {
        return 1;
    }

    private static int Return2()
    {
        return 2;
    }

发出对 lambda 表达式的调用

Emit a call to a lambda expression

c#

reflection.emit