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Resolved Cannot access an array of a specific Object from .NET C# via COM
  1. Issue
0 Votes
  1. achuta twameva
  2. PowerBuilder
  3. Saturday, 25 January 2020 09:31 AM UTC

Hi all,

I am facing a strange issue while fetching an array of a specific object type from .NET C# to PB 11.2 (classic) via COM.

My C# code is as follows:

namespace RestHandler
{
    [ComVisible(true)]
    [Guid("3CF8AB49-5E7D-4719-B277-5047C6A42FAE")]
    public interface IReturnArray
    {
        String getString();
        String[] getStringArray();
        myClass getClass();
        myClass[] getClassArray();
    }

    [ComVisible(true)]
    [Guid("EDA88A40-73BC-4e61-B134-DD07D42E91E0")]
    public class myClass
    {
        [ComVisible(true)]
        [MarshalAs(UnmanagedType.BStr)]
        public string myString;


        [ComVisible(true)]
        public int myInt;
    }

    [ComVisible(true)]
    [Guid("8035E886-82F1-47c7-AE7D-087DD0A555CE")]
    [ClassInterface(ClassInterfaceType.None)]
    public class ReturnArray : IReturnArray
    {
        public ReturnArray()
        {
        }
        public String getString()
        {
            return "Hello World";
        }
        public String[] getStringArray()
        {
            String[] myArray = new String[2] { "Hello", "World" };
            return myArray;
        }
        public myClass getClass()
        {
            myClass temp =
                new myClass
                {
                    myString = "Hello",
                    myInt = 1
                };
            return temp;
        }
        public myClass[] getClassArray()
        {
            myClass[] myArray =
                new myClass[]{
                    new myClass(){
                        myString = "Hello",
                        myInt = 1
                    },
                    new myClass(){
                        myString = "World",
                        myInt = 2
                    },
                    new myClass(){
                        myString = "This is Bruce",
                        myInt = 3
                    }
               };
            return myArray;
        }
    }
}

My PB code is as follows:

oleobject      retarray
int                    li_rc
int                    li_index, li_count
int                    li_x
String               ls_string
String               ls_stringarray[]
oleobject          loo_class
oleobject          loo_classarray[]

retarray = CREATE OleObject
li_rc = retarray.ConnectToNewObject ( "RestHandler.ReturnArray" )

ls_string = retarray.getString()
MessageBox ( "getString", ls_string )

ls_stringarray = retarray.getStringArray()
MessageBox ( "getStringArray", ls_stringarray[1] )

loo_class = retarray.GetClass()
MessageBox ( "GetClass", String ( loo_class.myString )) /*single object works*/
Destroy loo_class

loo_classarray = retarray.GetClassArray()
st_1.Text = loo_classarray[1].myString /*null error, array of object does not work?*/

retarray.DisconnectObject()

Destroy retarray

This is all Bruce Armstrong sample codes on some other forum. In there, it's mentioned this works. Strangely, when I return a single object from C#, I can access it via a corresponding OLEObject in PB. Now, when I return an array of an object (Employee[]), I am trying to convert that into an array of OLEObject in PB and the number of objects in this OLEObject array is indeed correct in PB. However, all the OLEObject within this array is null; therefore I am getting a null reference exception in PB at the following line:

st_1.Text = loo_classarray[1].myString /*null error, array of object does not work?*/

Does anyone here have any idea why? I have already spent hours trying to find the reason.

Thanking you in advance,

-A

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