import UIKit

class ViewController:UIViewController, UIPickerViewDelegate, UIPickerViewDataSource{
    
    var pickerView:UIPickerView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        pickerView = UIPickerView()
        //将dataSource设置成自己
        pickerView.dataSource = self
        //将delegate设置成自己
        pickerView.delegate = self
        //设置选择框的默认值
        pickerView.selectRow(1,inComponent:0,animated:true)
        pickerView.selectRow(2,inComponent:1,animated:true)
        pickerView.selectRow(3,inComponent:2,animated:true)
        self.view.addSubview(pickerView)
        
        //建立一个按钮，触摸按钮时获得选择框被选择的索引
        let button = UIButton(frame:CGRect(x:0, y:0, width:100, height:30))
        button.center = self.view.center
        button.backgroundColor = UIColor.blue
        button.setTitle("获取信息",for:.normal)
        button.addTarget(self, action:#selector(ViewController.getPickerViewValue),
                         for: .touchUpInside)
        self.view.addSubview(button)
    }
    //设置选择框的列数为3列,继承于UIPickerViewDataSource协议
    func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return 3
    }
    
    //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 9
    }
    
    //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)+"-"+String(component)
    }
    
    //触摸按钮时，获得被选中的索引
    @objc func getPickerViewValue(){
        let message = String(pickerView.selectedRow(inComponent: 0)) + "-"
            + String(pickerView!.selectedRow(inComponent: 1)) + "-"
            + String(pickerView.selectedRow(inComponent: 2))
        let alertController = UIAlertController(title: "被选中的索引为",
                                                message: message, preferredStyle: .alert)
        let okAction = UIAlertAction(title: "OK", style: .cancel, handler: nil)
        alertController.addAction(okAction)
        self.present(alertController, animated: true, completion: nil)
    }
}

2，调整选择框的尺寸

UIPickerView 用 frame 和 center 两个属性设置整个选择框的大小和位置。
如果要调整内部列的宽度，需要实现 UIPickerViewDelegate 协议类中 pickerView:widthForComponent 方法设置
如果要调整内部行高，则需要实习上述协议类中 pickerView:rowHeightForComponent 方法设置

//设置列宽
func pickerView(_ pickerView: UIPickerView, widthForComponent component: Int) -> CGFloat {
    if(0 == component){
        //第一列变宽
        return 100
    }else{
        //第二、三列变窄
        return 30
    }
}

//设置行高
func pickerView(_ pickerView: UIPickerView, rowHeightForComponent component: Int)
    -> CGFloat {
    return 50
}

3，将图片作为选择框选项

选择框选项的内容，除了可以使字符串类型的，还可以是任意UIView类型的元素。比如我们将选项内容设置为图片：

func pickerView(_ pickerView: UIPickerView, viewForRow row: Int, forComponent component: Int,
                reusing view: UIView?) -> UIView {
    let image = UIImage(named:"icon_"+String(row))
    let imageView = UIImageView()
    imageView.image = image
    return imageView
}

4，检测响应选项的选择状态

func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int,
                inComponent component: Int) {
    //将在滑动停止后触发，并打印出选中列和行索引
    print(component)
    print(row)
}

func pickerView(_ pickerView: UIPickerView, viewForRow row: Int,
                forComponent component: Int, reusing view: UIView?) -> UIView {
    var pickerLabel = view as? UILabel
    if pickerLabel == nil {
        pickerLabel = UILabel()
        pickerLabel?.font = UIFont.systemFont(ofSize: 13)
        pickerLabel?.textAlignment = .center
    }
    pickerLabel?.text = String(row)+"-"+String(component)
    pickerLabel?.textColor = UIColor.blue
    return pickerLabel!
}