So if you don't have such classes, why are you using them? You have to create a subclass of QDialog that uses your uic generated code to initialise itself which is explained in the link you're constantly being pointed to.

Please, understand, there is nothing magical going on here. If you don't implement a class, you can't use it - it won't be created out of thin air. I asked you about your C++ knowledge and I was given an empty answer, but from what I see you don't know much about it. So I repeat Jacek's suggestion to take a good book about C++, be it either C++ Primer, Thinking in C++ (available online) or even Symfonia C++.

The problem here is that if we don't give you exact code you are to copy and paste into your files, there is no way you're going to obtain the result you want, because you don't seem to try to do anything by yourself. It seems that you know what to do, because you implemented the exact same thing that is required here with the main window. I just can't seem to understand why don't you repeat the exact same approach with the dialog.
We're all trying to teach you something here, but it seems we're doing something wrong, so please explain us what exactly you don't know how to do and I'm speaking of some fundamental things - like subclassing, creating variables, single or multiple inheritance, etc. Is this all known to you? Do you have any trouble handling those basics?