Navegação entre meses

.swift

import Foundation

class NavigationMonth{    
    var current = Date()
    var next : Date{return Calendar.current.date(byAdding: .month, value: 1, to: current)!}
    var before : Date{return Calendar.current.date(byAdding: .month, value: -1, to: current)!}

    init() {} // deve possuir um inicializador em branco  
    
    init(date : Date) {
        current = date
    }
}


//exemplo de implemantacao
let dateFormater = DateFormatter()
dateFormater.dateFormat = "MMMM"
var month = NavigationMonth()

//altere para que seja sua @IBAction no butao 'avancar'
func next() -> String{
    let nextMonthString = dateFormater.string(from: month.next)
    month = NavigationMonth(date: month.next)
    return nextMonthString
}

//altere para que seja sua @IBAction no butao 'voltar'
func before() -> String{
    let beforeMonthString = dateFormater.string(from: month.before)
    month = NavigationMonth(date: month.before)
    return beforeMonthString
}