Question

这是我第一次涉足生成的CIL，所以请忍受我的无知。我正在寻找一个简单的DynamicMethod，它可以读取POCO的字段，并将它们填入object[]。不需要类型转换。我把所有的东西放在一起，你能帮忙完成它吗？

Type t = typeof(POCO);

DynamicMethod dm = new DynamicMethod("Get" + memberName,typeof(MemberType), new Type[] { objectType }, objectType);
ILGenerator il = dm.GetILGenerator();

// Load the instance of the object (argument 0) onto the stack
il.Emit(OpCodes.Ldarg_0);

// get fields
FieldInfo[] fields = t.GetFields();

// how do I create an array (object[]) at this point?

// per field
foreach (var pi in fields) {

    // Load the value of the object's field (fi) onto the stack
    il.Emit(OpCodes.Ldfld, fi);

    // how do I add it into the array?

}

// how do I push the array onto the stack?

// return the array
il.Emit(OpCodes.Ret);

Answer 1

您可以使用此代码生成已编译的lambda表达式。

public static Func<T, object[]> MakeFieldGetter<T>() {
    var arg = Expression.Parameter(typeof(T), "arg");
    var body = Expression.NewArrayInit(
        typeof(object)
    ,   typeof(T).GetFields().Select(f => (Expression)Expression.Convert(Expression.Field(arg, f), typeof(object)))
    );
   return (Func<T, object[]>)Expression
        .Lambda(typeof(Func<T, object[]>), body, arg)
        .Compile();
}

这相当于以下手动编写的代码：

object[] GetFields(MyClass arg) {
    return new object[] {
        // The list of fields is generated through reflection
        // at the time of building the lambda. There is no reflection calls
        // inside the working lambda, though: the field list is "baked into"
        // the expression as if it were hard-coded manually.
        (object)arg.Field1
    ,   (object)arg.Field2
    ,   (object)arg.Field3
    };
}

此代码也会生成IL，但不是您手动编写，而是让Lambda Compile方法为您执行此操作。

这是working demo on ideone。

如何使用CIL将POCO转换为数组？

1 个答案: