Deriving by multiple Interfaces containing same members with different data types

Question

I have following situation:

using System.Data;

namespace TestClass
{
    //this is a class generated by a wsdl and may not be changed
    public partial class MyTableClass : DataTable
    {
        public MyRowClass this[int index]
        {
            get { return ((MyRowClass) (this.Rows[index])); }
        }

        public partial class MyRowClass : DataRow
        {
            protected internal MyRowClass(DataRowBuilder builder)
                : base(builder)
            {
            }
        }
    }

    //in this partial class I am able to extend the wsdl class by my own interfaces
    public partial class MyTableClass : IDetailTable
    {
        IDetailRow IDetailTable.this[int index]
        {
            get { return this[index]; }
        }

        public partial class MyRowClass : IDetailRow
        {
        }
    }

    public interface IBaseTable
    {
        IBaseRow this[int index] { get; }
    }

    public interface IDetailTable : IBaseTable
    {
        new IDetailRow this[int index] { get; }
    }

    public interface IBaseRow
    {
    }

    public interface IDetailRow : IBaseRow
    {
    }
     }

The first part is a class generated by a wsdl definition. I have no ability to change anything here. I have many wsdl definition files, most are very similar. So I want to define common interfaces for all, which will make me handle them easier in my code. So my idea was to extend them by a partial class definition like above.

But I get an error here, and I have no idea why and what I should do here:

Error 1 'TestClass.MyTableClass' does not implement interface member 'TestClass.IBaseTable.this[int]'. 'TestClass.MyTableClass.this[int]' cannot implement 'TestClass.IBaseTable.this[int]' because it does not have the matching return type of 'TestClass.IBaseRow'. c:\users\mag\documents\visual studio 2012\Projects\TestClass\TestClass\Class1.cs 6 24 TestClass

Only the base interfaces are implemented, not the derived detail interfaces. But why?

Answer 1

C# only supports single-inheritance, i.e., each class can only extend one from one superclass. However, you have MyTableClass extending DataTable in your first partial class, and IDetailTable in the second. That's what's causing the compilation error.

I think what your really trying to get at is that the second partial class should actually extend from the wsdl definition class. So I would change

public partial class MyTableClass : IDetailTable

to

public class MyAwesomeTableClass : MyTableClass