Problem creating new Telerik DataSource implementation: "does not implement inherited abstract member 'DataSource.CreateClone()'"

Question

I'm investigating the behavior of Telerik Reporting DataSources because I have the need to implement a new complex DataSource that coordinates with another process providing data to Telerik in a lazy way.

For now, I want to study how Telerik talks to a specified DataSource by implementing a mock class that implements directly DataSource class.

class MockDataSource : DataSource
{
    internal override object CreateClone()
    {
        throw new NotImplementedException();
    }
}

I added CreateClone method because the compiler shows me the following error:

Error CS0534 'MockDataSource' does not implement inherited abstract member 'DataSource.CreateClone()'

but even with the added method the above error doesn't disappear, and also the added method seems to override nothing:

Error CS0115 'MockDataSource.CreateClone()': no suitable method found to override

I'm pretty new to C#, but I can't figure out why this happens; also Telerik documentation doesn't state anywhere the feasibility of a custom DataSource which is not one of the provided: https://docs.telerik.com/reporting/connecting-to-data-data-source-components.

Answer 1

The reason of those errors resides in the visibility modifier of the abstact method CreateClone(): inspecting library code decompiled from the DLL with the help of JetBrains Rider, it is possible to see that the method is declared as internal:

[...]

namespace Telerik.Reporting
{
  [SRCategory("DataSources_Category")]
  [ToolboxItemFilter("VS.Telerik.Reporting.14.1.20.513", ToolboxItemFilterType.Require)]
  public abstract class DataSource : Component, ISimpleDataSource, IDataSource, INamedObject, ICloneable
  {
    [...]

    internal abstract object CreateClone();

    [...]
  }
}

Because of that, the method we need to override is not visible outside of Telerik's assembly, so it is not possible to actually extend the DataSource abstract class from a third-party assembly.