Validation in MVP WinForms Application

Question

I am creating a Windows Forms application that reads various tables from a database into a DataSet in order to display said tables in multiple DataGridViews . Rather than putting all my code in the code-behind file, I have started doing some research on different design patterns, and have found many articles/threads with the consensus that MVP is the best option for WinForms .

After doing a few tutorials, and starting to organize my code using the MVP pattern; I have placed my DataSet in what would be the Model, most of the logic in the Presenter, and everything else in the View.

My question is: where should I place the validation of user input? I do not want the user to be able to enter invalid values into the DataGridView s, and if they happen to do so, I would like to let them know the row/cell that has the error. Previously, I would handle the RowValidating event and check the row and cells of the DataGridView for any errors, and then display a message accordingly, but this seems to not fit within the MVP pattern.

Should I leave the validation in the view, or should it be moved elsewhere?

Answer 1

IMHO you should keep the view (the form) as simple as possible. You can indeed subscribe for the RowValidating event and call the presenter (presenter.ValidateRow(...)) from there and pass to it the info and let it handle the validation. The presenter on his turn can ask the model for some info if the validation logic happens to be complex and has to go all the way down (to the DB for example). It is the presenter's responsibility for how to handle the errors. When the validation process completes it's the presenter's job to call a method or set a property on the view in order to display failure or success. Remember that your view is just a "window" to the state of your business logic (objects). Ask yourself the question "Is my program going to work if I swap this specific view with another implementing the same interface but not written by me?". You may want to take a look at this http://msdn.microsoft.com/en-us/magazine/ee336019.aspx article for further clarification on MVP pattern.