NSTableView and data validation?

Question

In order to properly learn Objective-C and the Cocoa framework, I have started building a CoreData application, but I'm a bit at a loss on how to properly provide data validation when an item is being edited in an NSTableView.

My model has an entity called "Business" with two string properties: a name and an issued tax number. The second property must have a length of exactly 10 characters. This entity's objects are displayed and edited in an NSTableView, through an NSArrayController bound to the Business entity and the app's managedObjectContext.

What I would like to do is: - the user starts editing the tax number in the appropriate cell (NSTextFieldCell) of the tableview. - when pressing Enter, the new value is validated, i.e. checks to see that the new value has a length of 10 characters. If validation fails, an alert sounds and the cell keeps being focused. - pressing Escape restores the old value and the cell loses focus.

What is the proper way to perform this validation?

Answer 1

See the Managed Object Validation chapter of the Core Data Programming Guide.

Answer 2

If you are using bindings, you can check the "Validates Immediately" in the binding for cell value. That will call the validation method for the managed object.