Can I have auto-properties in a COM Interface

Question

I currently have an interface for a COM component that is something like this:

[ComVisible(true), InterfaceType(ComInterfaceType.InterfaceIsIUnknown), Guid("aa950e58-7c6e-4818-8fc9-adecbc7a8f14")]
    public interface MyIObjects
    {
        void set_price(float rx);
        void set_size(long rx);

        float get_price();
        long get_size();
    }

Now is there a simple shortcut that might reduce two lines of the following to one line

            void set_price(float rx);
            float get_price();

I know in classes I can do something like this

int Price { get; set; }

but will this work in an interface ?

Yes a visual studio feature or a macro (but C# doesnt have macros) — MistyD
– MistyD, Commented May 23, 2013 at 16:54
I think Resharper has something along that lines, but I can't comment for sure. — Chris Sinclair
– Chris Sinclair, Commented May 23, 2013 at 16:55
Oh, if your question is only "can I have auto-properties in an interface", then the answer is "yes". Thought you were looking for a keyboard/function shortcut helper in Visual Studio that would do it automatically (like Refactor -> Extract Method) and update all references/usages to use standard get/set syntax rather than invoking the non-existent methods. — Chris Sinclair
– Chris Sinclair, Commented May 23, 2013 at 16:56
@ChrisSinclair I believe his question is "Can I have auto-proerties in a COM Interface", is the answer still "Yes" in that case? — Scott Chamberlain
– Scott Chamberlain, Commented May 23, 2013 at 16:58

Scott Chamberlain · Accepted Answer · 2013-05-23 18:51:30Z

1

COM only cares about interfaces, not about their implementation. You already declare a property with a syntax that resembles an auto-property definition.

[ComVisible(true), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
public interface IMyObjects
{
    float price { get; set; }
    int size { get; set; }
}

How you implement the property is entirely up to you. And yes, using an auto-property in the class that implements the interface is fine.

[ComVisible(true), ClassInterface(ClassInterfaceType.None)]
public class MyObjects : IMyObjects {
    public float price { get; set; }
    public int size { get; set; }
}

Note that the long type as it appears in COM type libraries or native code is the same as the int type in C#.

Here is what the IDL definition of the interface would be (assuming inside the namespace CSDllCOMServer)

[
  odl,
  uuid(AA950E58-7C6E-4818-8FC9-ADECBC7A8F14),
  version(1.0),
  oleautomation,
  custom(0F21F359-AB84-41E8-9A78-36D110E6D2F9, "CSDllCOMServer.MyIObjects")

]
interface MyIObjects : IUnknown {
    [propget]
    HRESULT _stdcall price([out, retval] single* pRetVal);
    [propput]
    HRESULT _stdcall price([in] single pRetVal);
    [propget]
    HRESULT _stdcall size([out, retval] long* pRetVal);
    [propput]
    HRESULT _stdcall size([in] long pRetVal);
};

edited May 23, 2013 at 18:51

Scott Chamberlain

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answered May 23, 2013 at 18:35

Hans Passant

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1 Comment

Scott Chamberlain Over a year ago

You covered really well what I was going to go over in my answer (you just beat me to it) I added in the IDL definition for the sample interface in to your answer (I was going to put in my own answer).

Daniel A. White · Accepted Answer · 2013-05-23 16:56:20Z

0

You can declare properties in interfaces just fine!

answered May 23, 2013 at 16:56

Daniel A. White

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2 Comments

Scott Chamberlain Over a year ago

I believe his question is "Can I have auto-proerties in a COM Interface", does the fact that this will be used for COM and possibly consumed by non .NET programs affect the answer? (I am not saying it does, I just think that factor needs clarification)

MistyD Over a year ago

How would the implementation of this interface look like if I used an auto-property ?

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