ViewModel.swift

import Foundation

class ViewModel: NSObject
{
    struct SerializationKey
    {
        static let query = "query"
        static let hasValidValues = "hasValidValues"
    }

    var query: String = ""
    {
        willSet
        {
            self.willChangeValueForKey(SerializationKey.hasValidValues)
        }
        didSet
        {
            self.didChangeValueForKey(SerializationKey.hasValidValues)
        }
    }

    var hasValidValues: Bool
    {
        return !query.isEmpty
    }
}