how to use UIPicker dataSource

Question

I use the Xcode 8 and swift 2.3, but I met a problem the UIPickerView.dataSource = (self as! UIPickerViewDataSource) doesn't work when I try to use func of UIPicker, this is my code:

import UIKit

class ViewController: UIViewController {

    let Num = ["1","2","3","4","5","6"]

    @IBOutlet weak var UIPicker: UIPickerView!
    override func viewDidLoad() {
        super.viewDidLoad()

        func numberOfRows(inComponent component: Int) -> Int {return 1}

        func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {return Num.count}

        func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {return Num[row]}

        UIPicker.dataSource = (self as! UIPickerViewDataSource)
        UIPicker.delegate = (self as! UIPickerViewDelegate)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}

When I run my code, Xcode warning the code:

Could not cast value of type 'test.ViewController' (0x1000bd8c0) to 'UIPickerViewDataSource' (0x1ab289738). 2016-06-29 15:33:35.079300 test[474:98176] Could not cast value of type 'test.ViewController' (0x1000bd8c0) to 'UIPickerViewDataSource' (0x1ab289738).

Answer 1

Add UIPickerViewDataSource and UIPickerViewDelegate to the class declaration:

class ViewController: UIViewController, UIPickerViewDataSource, UIPickerViewDelegate

and don't use type casting using self:

override func viewDidLoad() {
    super.viewDidLoad()

    UIPicker.dataSource = self
    UIPicker.delegate = self
}

Also you must move your methods out of viewDidLoad function, and correct them a bit:

func numberOfComponentsInPickerView(pickerView: UIPickerView) -> Int {return 1}

func pickerView(pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {return Num.count}

func pickerView(pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {return Num[row]}

Note that I highly recommend you to rename your Num and UIPicker properties to num and picker, so you will not mix them with class names

Upd: full ViewController code:

class ViewController: UIViewController, UIPickerViewDataSource, UIPickerViewDelegate {

    let Num = ["1","2","3","4","5","6"]

    @IBOutlet weak var UIPicker: UIPickerView!
    override func viewDidLoad() {
        super.viewDidLoad()

        UIPicker.dataSource = self
        UIPicker.delegate = self
    }

    func numberOfComponentsInPickerView(pickerView: UIPickerView) -> Int {return 1}
    func pickerView(pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {return Num.count}
    func pickerView(pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {return Num[row]}
}