Reflection Emit：如何为此构建构造函数

Question

我要动态构建的代码如下：

public class Sample
{
    public Sample()
    {
        Items = new ObservableTestCollection<Sample>(this);
    }
    public Sample(IEnumerable<Sample> source)
    {
        Items = new ObservableTestCollection<Sample>(this, source);
    }
    public ObservableTestCollection<Sample> Items;
}

ObservableTestCollection的来源如下：

public class ObservableTestCollection<T> : ObservableCollection<T>
{
    public T Parent;       
    public ObservableTestCollection(T parent)
    {
        Parent = parent;
    }
    public ObservableTestCollection(T parent, IEnumerable<T> source) : base(source)
    {
        Parent = parent;
    }
}

我写的代码是：

const string assemblyName = "SampleAssembly";
const string fieldName = "Items";
const string typeName = "Sample";
const string assemblyFileName = assemblyName + ".dll";

AppDomain domain = AppDomain.CurrentDomain;
AssemblyBuilder assemblyBuilder = domain.DefineDynamicAssembly(new AssemblyName(assemblyName), AssemblyBuilderAccess.RunAndSave);
ModuleBuilder moduleBuilder = assemblyBuilder.DefineDynamicModule(assemblyName, assemblyFileName);

TypeBuilder typeBuilder = moduleBuilder.DefineType(typeName, TypeAttributes.Class | TypeAttributes.Public);

Type[] ctorParameters = new Type[] { typeBuilder };
Type typeOfCTS = typeof(ObservableTestCollection<>);
Type genericTypeOTS = typeOfCTS.MakeGenericType(typeBuilder);


FieldBuilder fieldBuilder = typeBuilder.DefineField(fieldName, genericTypeOTS, FieldAttributes.Public);

        //first constructor
ConstructorBuilder ctorBuilder = typeBuilder.DefineConstructor(MethodAttributes.Public, CallingConventions.HasThis, Type.EmptyTypes);
ILGenerator generator = ctorBuilder.GetILGenerator();
        generator.Emit(OpCodes.Ldarg_0); //load this
        generator.Emit(OpCodes.Call, typeof(object).GetConstructor(Type.EmptyTypes)); //call object constructor

var ci = typeOfCTS.GetConstructors()[0];
generator.Emit(OpCodes.Newobj, ci);            
generator.Emit(OpCodes.Stfld, fieldBuilder); // store into Items
generator.Emit(OpCodes.Ret); //return

//second constructor
var typeOfIE = typeof(IEnumerable<>);
var genericTypeIE = typeOfIE.MakeGenericType(typeBuilder);          
ctorParameters = new Type[] {genericTypeIE };
ctorBuilder = typeBuilder.DefineConstructor(MethodAttributes.Public, CallingConventions.HasThis, ctorParameters);

ctorParameters = new Type[] { typeBuilder, genericTypeIE };
generator = ctorBuilder.GetILGenerator();
generator.Emit(OpCodes.Ldarg_0); //load this

ci = typeOfCTS.GetConstructors()[1];
generator.Emit(OpCodes.Newobj, ci);
generator.Emit(OpCodes.Stfld, fieldBuilder); // store into Items
generator.Emit(OpCodes.Ret); //return
Type type = typeBuilder.CreateType();
var obj = Activator.CreateInstance(type);
assemblyBuilder.Save(assemblyFileName);

我无法创建示例实例。

谁能帮我解决这个问题？

非常感谢您的帮助。

Answer 1

您的程序无效，因为您尝试创建一个实例 "ObservableTestCollection of Sample" 但 Sample 是一个类型构建器。

如果泛型参数是类型构建器而不是 "MakeGenericType"，请使用 TypeBuilder.GetConstructor(Type, ConstructorInfo) 获取泛型构造函数。

Answer 2

此错误的原因是调用了开放泛型类型的构造函数。您需要使用 TypeBuilder 作为泛型参数获取封闭泛型类型的构造函数。获取解释 here.

的 ConstructorInfo 存在一些问题

所以解决方案是使用以下参数调用 TypeBuilder.GetConstructor(Type, ConstructorInfo) 静态方法（正如@TonyTHONG 已经提到的）：

Type 必须是在 TypeBuilder 上关闭的通用类型，在您的情况下 typeof(ObservableTestCollection<>).MakeGenericType(typeBuilder)；
ConstructorInfo 您可以从开放泛型类型中获得，在您的情况下 typeof(ObservableTestCollection<>).

您可以在下面查看针对您的问题的代码示例：

        const string assemblyName = "SampleAssembly";
        const string fieldName = "Items";
        const string typeName = "Sample";
        const string assemblyFileName = assemblyName + ".dll";

        var domain = AppDomain.CurrentDomain;
        var assemblyBuilder = domain.DefineDynamicAssembly(new AssemblyName(assemblyName), AssemblyBuilderAccess.RunAndSave);

        var moduleBuilder = assemblyBuilder.DefineDynamicModule(assemblyName, assemblyFileName);
        var typeBuilder = moduleBuilder.DefineType(typeName, TypeAttributes.Class | TypeAttributes.Public);

        var typeOfCts = typeof(ObservableTestCollection<>);
        var genericTypeOfCts = typeOfCts.MakeGenericType(typeBuilder);

        var fieldBuilder = typeBuilder.DefineField(fieldName, genericTypeOfCts, FieldAttributes.Public);

        //first constructor Sample()
        var ctorBuilder = typeBuilder.DefineConstructor(MethodAttributes.Public, CallingConventions.HasThis, Type.EmptyTypes);
        var obsCtor1 = typeOfCts.GetConstructors().First(c => c.GetParameters().Length == 1);
        obsCtor1 = TypeBuilder.GetConstructor(genericTypeOfCts, obsCtor1); //hack to get close generic type ctor with typeBuilder as generic parameter

        var generator = ctorBuilder.GetILGenerator();
        generator.Emit(OpCodes.Ldarg_0); //load this for base type constructor
        generator.Emit(OpCodes.Call, typeof(object).GetConstructors().Single());

        generator.Emit(OpCodes.Ldarg_0); //load this for field setter

        generator.Emit(OpCodes.Ldarg_0); //load this for ObservableTestCollection constructor
        generator.Emit(OpCodes.Newobj, obsCtor1); //call ObservableTestCollection constructor, it will put point to new object in stack

        generator.Emit(OpCodes.Stfld, fieldBuilder); // store into Items
        generator.Emit(OpCodes.Ret); //return

        //second constructor Sample(IEnumerable<Sample> source)
        var ctorParam = typeof(IEnumerable<>).MakeGenericType(typeBuilder);
        ctorBuilder = typeBuilder.DefineConstructor(MethodAttributes.Public, CallingConventions.HasThis, new Type[] { ctorParam } );
        obsCtor1 = typeOfCts.GetConstructors().First(c => c.GetParameters().Length == 2);
        obsCtor1 = TypeBuilder.GetConstructor(genericTypeOfCts, obsCtor1); //hack to get close generic type ctor with typeBuilder as generic parameter

        generator = ctorBuilder.GetILGenerator();
        generator.Emit(OpCodes.Ldarg_0); //load this for base type constructor
        generator.Emit(OpCodes.Call, typeof(object).GetConstructors().Single());

        generator.Emit(OpCodes.Ldarg_0); //load this for field setter

        generator.Emit(OpCodes.Ldarg_0); //load this for ObservableTestCollection constructor
        generator.Emit(OpCodes.Ldarg_1); //load IEnumerable for ObservableTestCollection constructor
        generator.Emit(OpCodes.Newobj, obsCtor1); //call ObservableTestCollection constructor, it will put point to new object in stack

        generator.Emit(OpCodes.Stfld, fieldBuilder); // store into Items
        generator.Emit(OpCodes.Ret); //return


        var type = typeBuilder.CreateType();
        var obj1 = Activator.CreateInstance(type);

        var parameter = Activator.CreateInstance(typeof(List<>).MakeGenericType(type));
        var obj2 = Activator.CreateInstance(type, parameter);
        assemblyBuilder.Save(assemblyFileName);

另外请记住，我只是通过将 ObservableTestCollection 放在与生成 Sample class 的代码不同的程序集中来设法运行它。

如果我没记错的话，您也在动态生成 ObservableTestCollection class。因此它可以在不分离程序集的情况下工作，特别是如果你对它们使用相同的AssemblyBuilder。

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