Validating user defaults when using NSDictionaryController and Swift

Question

I have a view-based table with an NSDictionaryController, the content of which is bound to NSUserDefaultsController in Interface Builder:

What is the correct way of validating the dictionary values in Swift? (The dictionary keys are automatically validated, and an error is raised for empty keys. I want to do the same for the dictionary values.)

Answer 1

Set the delegate of the text field in the cell to the delegate of the table view and implement control(_:isValidObject:).

Answer 2

You will need to implement a function as follows:

@objc func validateToken(_ ioValue: AutoreleasingUnsafeMutablePointer<AnyObject?>) throws {
    guard ioValue.pointee != nil else {
        // throw some error
    }
}

Your Cocoa Binding will look for that function via validateValue(_:forKey:).

For it to be found, the property specific validation function must be exposed to Objective-C, must be named according to the pattern validateInKey, must take a single, optional AnyObject pointer argument, and must throw (Apple Inc., 2018).

I am assuming that your binding points to a specific value in your dictionary.

Reference:

Apple Inc. (2018). validateValue(_:forKey:). Retrieved from https://developer.apple.com/documentation/objectivec/nsobject/1416754-validatevalue