swift 3 如何获取明天和昨天的日期(注意特殊情况)新月或新年

我正在 for each 月的数据日历工作

我因为特殊情况(索引越界)而崩溃

这是我的密码

class ViewController: UIViewController {
    var dateComponents: DateComponents!
    var TimeToday :[String] = []
    var TimeTomorrow :[String] = []
    var TimeYesterday :[String] = []
    override func viewDidLoad() {
        super.viewDidLoad()
        let dateDay = Date()
        let calendar = Calendar(identifier: .gregorian)
        dateComponents = calendar.dateComponents([.day, .month, .year], from: dateDay)
        done()
    }
    func done()  {
        //------ for tomorrow ------
        // month end day 31
        if (dateComponents.day! == 30){
            if(dateComponents.month! == 1 || dateComponents.month! == 4 || dateComponents.month! == 6 || dateComponents.month! == 7 || dateComponents.month! == 9 || dateComponents.month! == 11 ){
                TimeTomorrow.append("\(dateComponents.month!+1)")
            }
        // month end day 31
        }else if (dateComponents.day! == 31){
            if(dateComponents.month! == 3 || dateComponents.month! == 5 || dateComponents.month! == 8 ){
                TimeTomorrow.append("\(dateComponents.month!+1)")
            }else if(dateComponents.month! == 12){
                TimeTomorrow.append("\(dateComponents.year!+1)")
            }
         // month end day 29
        // special case for leap year i donot know how find it
        //****************************************************
            else if (dateComponents.day! == 29){
                if(dateComponents.month! == 2 || dateComponents.month! == 10  ){
                    TimeTomorrow.append("\(dateComponents.month!+1)")
                }
            }
        //------ for yesterday  ------
            if (dateComponents.month! == 12 || dateComponents.month! == 10 || dateComponents.month! == 8 || dateComponents.month! == 7 || dateComponents.month! == 5 || dateComponents.month! == 2){
                var day = dateComponents.date! - 1
                //fatal error: unexpectedly found nil while unwrapping an Optional value
                TimeYesterday.append("\(day)")
                TimeYesterday.append("30 - \(dateComponents.month! - 1)")
            }else {
                //////
            }
        }
    }
}