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6.6

Help with casting to a different class (upcasting?)

Asked by Jon500 in C# Programming Language

Tags: upcasting

I don't understand something basic about classes and inheritance (or perhaps I'm just tired after hours of programming?)...

I created my own class that derived from System.Data.DataTable:

public class MyTable : System.Data.DataTable
{ ... }

I did this because I want to carry along specific information in MyTable object that are useful to my application.

I have some database-wrapper code (let's call that myFunction()) that returns the data type System.Data.DataTable:

System.Data.DataTable dt = myFunction();

But want I want to do is return the results of myFunction into a object of type MyTable (let's call that object mt). I thought I could do this by simply casting it as follows:

MyTable mt = (MyTable)myFunction();

This compiles fine. And I thought this should work since MyTable is derived from DataTable. However, at runtime, I get a "Specified cast is not valid" exception at the code line above.

How can I get the System.Data.DataTable object value into my own MyTable object? Do I have to use a Copy method on the DataTable returned by myFunction?

Is what I'm trying to do called "upcasting"?

Thank you for your help.

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20091111-EE-VQP-92

Help with casting to a different class (upcasting?)

Asked by Jon500 in C# Programming Language

Tags: upcasting

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