c# - 为什么我无法在 C# 中使用 IL Generation 创建对象的实例？

Question

我有以下类(class):

private sealed class Person
{
    public string Name { get; }
    public int Age { get; }

    public Person(string name)
    {
        Name = name;
    }

    public Person(string name, int age)
    {
        Name = name;
        Age = age;
    }
}

以及以下动态创建 ConstructorInfo 实例的方法:

public static Func<object[], T> GetBuilder<T>(ConstructorInfo constructor)
{
    var type = constructor.ReflectedType;    
    var ctorParams = constructor.GetParameters();

    var dynamicMethod = new DynamicMethod("Create_" + constructor.Name, type, new[] { typeof(object[]) }, type, true);
    var ilGen = dynamicMethod.GetILGenerator();

    /*
     * Cast each argument of the input object array to the appropriate type
     * The order of objects should match the order set by the Ctor
     * It is also assumed the length of object array args is same length as Ctor args. 
     * Exceptions for the delegate that mean the above weren't satisfied: 
     * InvalidCastException, IndexOutOfRangeException
     */
    for (var i = 0; i < ctorParams.Length; i++)
    {
        // Push Object array
        ilGen.Emit(OpCodes.Ldarg_0);

        // Push the index to access
        ilGen.Emit(OpCodes.Ldc_I4, i);

        // Push the element at the previously loaded index
        ilGen.Emit(OpCodes.Ldelem_Ref);

        // Cast the object to the appropriate Ctor Parameter Type
        var paramType = ctorParams[i].ParameterType;
        ilGen.Emit(paramType.IsValueType ? OpCodes.Box : OpCodes.Castclass, paramType);
    }

    // Call the Ctor, all values on the stack are passed to the Ctor
    ilGen.Emit(OpCodes.Newobj, constructor);
    // Return the new object
    ilGen.Emit(OpCodes.Ret);

    // Create delegate from our IL, cast and return
    return (Func<object[], T>)dynamicMethod.CreateDelegate(typeof(Func<object[], T>));
}

然后我使用该方法为每个构造函数创建此类的两个实例:

var ctorOne = typeof(Person).GetConstructors(BindingFlags.Public | BindingFlags.Instance)[0];
var instanceBuilderOne = GetBuilder<Person>(publicCtor[0]);
var instanceOne = instanceBuilderOne(new object[] { "Foo"});
instanceOne.Name.Dump(); // is "Foo"

var ctorTwo = typeof(Person).GetConstructors(BindingFlags.Public | BindingFlags.Instance)[1];
var instanceBuilderTwo = GetBuilder<Person>(publicCtor[1]);
var instanceTwo = instanceBuilderTwo(new object[] { "Bar", 1});
instanceTwo.Name.Dump(); // is "Bar"
instanceTwo.Age.Dump(); // is 43603896

但是，对于 instanceTwo，我得到的不是 1，而是 43603896。

在相关构造函数中打断点确实显示 43603896 被传递给实例，但我不明白为什么!？

Answer 1

首先，OpCodes.Box 在这里显然是错误的，因为您想从对象中拆箱 int，而不是装箱。

现在 OpCodes.Unbox 所做的是取消装箱值并将未装箱值的 reference 推送到堆栈。该引用是您看到的而不是“1”。如果你想使用OpCodes.Unbox，正确的方法是这样的:

if (paramType.IsValueType) {
     ilGen.Emit(OpCodes.Unbox, paramType);
     ilGen.Emit(OpCodes.Ldobj, paramType);
}
else {
      ilGen.Emit(OpCodes.Castclass, paramType);
}

但是使用 OpCodes.Unbox_Any 会更容易，它基本上会做同样的事情，但在一行中:

ilGen.Emit(OpCodes.Unbox_Any, paramType);