C#: combine DllImport with inheritance?
public abstract class abstractClassA
{
    public abstract int abstractMethodA(int parameter);
}

public class usualClass : abstractClassA
{
    [DllImort("ExternalLib.dll")]
    public static extern abstractMethodA(int parameter);
}

abstractClassA instance = new usualClass();

public class usualClass : abstractClassA
{
    public extern override abstractMethodA(int parameter);
}

abstractClassA instance = new usualClass();

public abstract class AbstractClassA
{
    public abstract int AbstractMethodA(int parameter);
}

public class UsualClass : AbstractClassA
{
    [DllImport("ExternalLib.dll", EntryPoint = "abstractMethodA")]
    static extern int AbstractMethodAImport(int parameter);
    public override int AbstractMethodA(int parameter)
    {
        return AbstractMethodAImport(parameter);
    }
}

public abstract class AbstractClassA
{
    public abstract int AbstractMethodA(int parameter);
}

public class UsualClass : AbstractClassA
{
    public override int AbstractMethodA(int parameter)
    {
        return NativeMethods.AbstractMethodA(parameter);
    }
}

[SuppressUnmanagedCodeSecurity]
internal class NativeMethods
{
    [DllImport("ExternalLib.dll", EntryPoint = "abstractMethodA")]
    public static extern int AbstractMethodA(int parameter);
}

public abstract class abstractClassA
{
    public abstract int abstractMethodA(int parameter);
}

public class usualClass : abstractClassA
{
    [DllImort("ExternalLib.dll", EntryPoint="TheFunctionName")]
    private static extern abstractMethodAextern(int parameter);

    public override int abstractMethodA(int parameter)
    {
        return abstractMethodAextern(parameter);
    }
}