废话不多说，直接上代码

 @IBAction func SelectDatePick(_ sender: Any) {
        //初始化UIPickerView
        pickerView = UIPickerView()
        pickerView.dataSource = self
        pickerView.delegate = self
        //设置选择框的默认值
        pickerView.selectRow(0,inComponent:0,animated:true)
        //把UIPickerView放到alert里面（也可以用datePick）
        let alertController:UIAlertController=UIAlertController(title: "\n\n\n\n\n\n\n\n\n\n\n\n", message: nil, preferredStyle: UIAlertControllerStyle.actionSheet)
        alertController.addAction(UIAlertAction(title: "确定", style: UIAlertActionStyle.default){
            (alertAction)->Void in
            print("date select:" + String(self.pickerView.selectedRow(inComponent: 0)+1))
        })
        alertController.addAction(UIAlertAction(title: "取消", style: UIAlertActionStyle.cancel,handler:nil))
        let width = frameView.frame.width;
        pickerView.frame = CGRect(x: 10, y: 0, width: width, height: 250);
        alertController.view.addSubview(pickerView)
        self.present(alertController, animated: true, completion: nil)
    }
    var pickerView:UIPickerView!
    @IBOutlet weak var frameView: UIView!

    //设置选择框的列数为3列,继承于UIPickerViewDataSource协议
    func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return 1
    }
    //设置选择框的行数为9行，继承于UIPickerViewDataSource协议
    func pickerView(_ pickerView: UIPickerView,
                    numberOfRowsInComponent component: Int) -> Int {
        return 12
    }
    //设置选择框各选项的内容，继承于UIPickerViewDelegate协议
    func pickerView(_ pickerView: UIPickerView, titleForRow row: Int,
                    forComponent component: Int) -> String? {
        return String(row+1)+""+String("个月")
    }

fds.png

代码很简单，适用于UIPickerView跟DatePicker，还有其他的，有兴趣的朋友可以自己在去试试看别的哈
注解：
frameView:是我页面上面定义的一个view用来存放UIPickerVIew的宽度，可以直接无视
有任何问题请大家指出，谢谢！