VB6到C#interop:不能直接设置'object'类型的属性

鉴于以下C#类:

namespace ComTest
{
    [InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
    [Guid("A1D11BE5-40A1-4566-A1CA-418ABC76017C")]
    public interface IThing
    {
        [DispId(1)]
        void SetValue( object input );
        [DispId(2)]
        object Value {get; set;}
    }

    [ComVisible(true)]
    public class Thing: IThing
    {
        internal object PValue;

        public void SetValue(object input)
        {
            PValue = input;
        }

        public object Value
        {
            get
            {
                return PValue;
            }
            set
            {
                PValue = (object)value;
            }
        }

    }
}

谁能在VB6中解释以下行为？

Dim oThing as Thing
Dim input as Variant, output as Variant
input = "Some text"
Set oThing = new Thing
oThing.SetValue(input)    ' works fine
output = oThing.Value     ' works fine
Set oThing.Value = input  ' fails with runtime error '424': Object required

[new]我将程序集设置为COM可见,并检查标记为"注册COM互操作"的项目属性框("构建"选项卡).

正如您可能猜到的,该示例是我正在使用的实际类的简化版本.我比较了实际类和Thing类(下面)生成的TLB信息.标记为**的行可以在Thing类中找到,但不是实际的类(实际的coclass包含[default] dispinterface IThing),这个额外生成的接口_Thing似乎以两种方式改变了VBA中的行为:(1)属性将不再自动完成,(2)直接赋值给Value现在可以像贡献者找到的那样工作.有什么想法吗？

// Generated .IDL file (by the OLE/COM Object Viewer)
// 
// typelib filename: ThingLib.tlb
[
  uuid(92093AA7-870E-498A-8B80-97545D221E24),
  version(1.0),
  helpstring("AAA Testing COM interop")
]
library ThingLib
{
    // TLib :     // TLib : mscorlib.dll : {BED7F4EA-1A96-11D2-8F08-00A0C9A6186D}
    importlib("mscorlib.tlb");
    // TLib : OLE Automation : {00020430-0000-0000-C000-000000000046}
    importlib("stdole2.tlb");

    // Forward declare all types defined in this typelib
    dispinterface IThing;
**  interface _Thing;

    [
      uuid(7FC255DD-F82F-4B39-8755-9680A97033B5),
      version(1.0),
        custom({0F21F359-AB84-41E8-9A78-36D110E6D2F9}, "ComTest.IThing")    

    ]
    dispinterface IThing {
        properties:
        methods:
            [id(0x00000001)]
            void SetValue([in] VARIANT input);
            [id(0x00000002), propget]
            VARIANT Value();
            [id(0x00000002), propputref]
            void Value([in] VARIANT rhs);
    };

    [
      uuid(D96FB9C7-A0AF-35D3-A0F6-A07A9ED47984),
      version(1.0),
        custom({0F21F359-AB84-41E8-9A78-36D110E6D2F9}, "ComTest.Thing")
    ]
    coclass Thing {
**      [default] interface _Thing;
        interface _Object;
        dispinterface IThing;
    };

**    [
**      odl,
**      uuid(C309BDD0-239F-38AA-A057-254F8E01BD4B),
**      hidden,
**      dual,
**      oleautomation,
**        custom({0F21F359-AB84-41E8-9A78-36D110E6D2F9}, "ComTest.Thing")    
**    ]
**    interface _Thing : IDispatch {
**    };
};

Kris Erickso.. 5

将您的代码更改为:

Dim oThing as Thing
Dim input as Variant, output as Variant
input = "Some text"
Set oThing = new Thing
oThing.SetValue(input)    ' works fine
output = oThing.Value     ' works fine
Set oThing.Value = input  ' Change this line

一切都应该有效.(你必须在VB6中设置对象,你试图让一个对象,这只能用于原子类型).

将您的代码更改为:

Dim oThing as Thing
Dim input as Variant, output as Variant
input = "Some text"
Set oThing = new Thing
oThing.SetValue(input)    ' works fine
output = oThing.Value     ' works fine
Set oThing.Value = input  ' Change this line

一切都应该有效.(你必须在VB6中设置对象,你试图让一个对象,这只能用于原子类型).