Ok. Forduljunk a forráshoz:
Separate Domain from Presentation
You have GUI classes that contain domain logic.Separate the domain logic into separate domain classes
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Domain objects contain no visual code but all the business logic. This separates two complicated parts of the program into pieces that are easier to modify. It also allows multiple presentations of the same business logic. Those experienced in working with objects use this separation instinctively, and it has proved its worth.