如何将我的日期设置为昨天?

How to set my date into yesterday?

我正在尝试在我的项目中创建 UIDatePicker,最大日期应该是昨天而不是当前日期。有没有办法将所选日期设置为昨天而不是选择当前日期?

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var datePicker: UIDatePicker!

    override func viewDidLoad() {
        super.viewDidLoad()

        datePicker.datePickerMode = .Date

        let yesterday = NSCalendar.currentCalendar().dateByAddingUnit(.Day, value: -1, toDate: NSDate(), options: [])!

        datePicker.maximumDate = NSCalendar.currentCalendar().dateBySettingHour(12, minute: 0, second: 0, ofDate: yesterday, options: [])
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}