Question

I’m not sure if this has been asked or not yet, but how much logic should you put in your UI classes?

When I started programming I used to put all my code behind events on the form which as everyone would know makes it an absolute pain in the butt to test and maintain. Overtime I have come to release how bad this practice is and have started breaking everything into classes.

Sometimes when refactoring I still have that feeling of ‘where should I put this stuff’, but because most of the time the code I’m working on is in the UI layer, has no unit tests and will break in unimaginable places, I usually end up leaving it in the UI layer.

Are there any good rules about how much logic you put in your UI classes? What patterns should I be looking for so that I don’t do this kind of thing in the future?

Answer 1

Just logic dealing with the UI.

Sometimes people try to put even that into the Business layer. For example, one might have in their BL:

if (totalAmount < 0)      color = 'RED'; else      color = 'BLACK'; 

And in the UI display totalAmount using color — which is completely wrong. It should be:

if (totalAmount < 0)      isNegative = true; else      isNegative = false; 

And it should be completely up to the UI layer how totalAmount should be displayed when isNegative is true.