需求如下：

• 有開(kāi)始時(shí)間、結(jié)束時(shí)間勾哩、提醒時(shí)間三個(gè)cell需要彈出時(shí)間選擇器
• 開(kāi)始時(shí)間和結(jié)束時(shí)間只顯示日期死嗦，提醒時(shí)間顯示日期和時(shí)間（小時(shí)和分鐘）
• 選擇好時(shí)間好，開(kāi)始時(shí)間和結(jié)束時(shí)間所在的cell顯示文案只有年月日月劈，提示時(shí)間所在cell顯示的文案有年月日小時(shí)分鐘
• 編輯提醒時(shí)間時(shí)（之前已經(jīng)設(shè)置過(guò)提醒時(shí)間了，現(xiàn)在想改這個(gè)提醒時(shí)間）藤乙，打開(kāi)DatePicker的時(shí)候猜揪，DatePicker的當(dāng)前日期需要是之前設(shè)定的日期，不能是現(xiàn)在的日期

實(shí)現(xiàn)方法如下：

    func updateDateLabel(indexPath:NSIndexPath) {
        let formatter = NSDateFormatter()
        formatter.dateStyle = .MediumStyle        
        switch indexPath.row {
        case 6 :
            formatter.timeStyle = .ShortStyle
            dueDateLabel.text = formatter.stringFromDate(dueDate)
        case 2:
            startDateLabel.text = formatter.stringFromDate(startDate)
        case 3:
            endDateLabel.text = formatter.stringFromDate(endDate)
        default:
            print("erro.....")
        }        
    }
    
    override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
        switch indexPath.row {
        case 2:
            showDatePicker(indexPath)
        case 3:
            showDatePicker(indexPath)
        case 6:
            showDatePicker(indexPath)
        default:
            print("點(diǎn)擊了其他行")
        }        
    }

   func showDatePicker(indexPath: NSIndexPath) {
        let alert = UIAlertController(title: "", message: "\n\n\n\n\n\n\n\n\n\n\n\n\n", preferredStyle: .ActionSheet)
        let cancel = UIAlertAction(title: "取消", style: .Cancel , handler: nil)
        
        let datePicker = UIDatePicker()
        switch indexPath.row {
        case 2:
            datePicker.datePickerMode = .Date
            datePicker.setDate(startDate, animated: false)
        case 3:
            datePicker.datePickerMode = .Date
            datePicker.setDate(endDate, animated: false)
        case 6:
            datePicker.datePickerMode = .DateAndTime
            datePicker.setDate(dueDate, animated: false)
        default:
            print("點(diǎn)擊了其他行")
        }
        
        alert.view.addSubview(datePicker)
        
        
        let confirmOk = UIAlertAction(title: "確定", style: .Destructive) { (UIAlertAction) in
            switch indexPath.row {
            case 6: self.dueDate = datePicker.date
            case 2: self.startDate = datePicker.date
            case 3: self.endDate = datePicker.date
            default: print("erro")
            }
            self.updateDateLabel(indexPath)
        }
        
        alert.addAction(cancel)
        alert.addAction(confirmOk)
        presentViewController(alert, animated: true, completion: nil)
        
    }