How can I populate a picker view depending on the selection of another picker view in Swift?

Question

Looking for a solution to populate a picker view depending on the selection of another picker view within the same view controller. The first selects a category. The second the items of that category.

Here's what I (Swift beginner) came up with:

import UIKit

class ViewController: UIViewController, UIPickerViewDataSource,      UIPickerViewDelegate {

var countryClasses = ["US", "EU", "JP"]
var usItems = ["usitem1", "usitem2", "usitem3", "usitem4", "usitem5"]
var euItems = ["euitem1", "euitem2", "euitem3", "euitem4", "euitem5"]
var jpItems = ["jpitem1", "jpitem2", "jpitem3", "jpitem4", "jpitem5"]

@IBOutlet weak var countryPicker: UIPickerView!

@IBOutlet weak var itemPicker: UIPickerView!

override func viewDidLoad() {
    super.viewDidLoad()
    self.countryPicker.dataSource = self;
    self.countryPicker.delegate = self;
    self.itemPicker.dataSource = self;
    self.itemPicker.delegate = self;
}

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

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

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

}

Answer 1

As both the Pickers are using the same delegate you are going to need a way to identify them when your delegate methods run, also your current Array structure means you are going to need a way to select each item array as and when the country is selected.

Create a store for the selected item array.

var selectedItemsArray = []

Add some checks to your delegate methods.

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

func pickerView(pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
    if pickerView == countryPicker {
        return countryClasses.count
    } else if pickerView == itemPicker {
        return selectedItemsArray.count
    }
    return 0
}

func pickerView(pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String! {
    if pickerView == countryPicker {
        return countryClasses[row]
    } else if pickerView == itemPicker {
        return selectedItemsArray[row]
    }
    return 0
}

Then you need to implement did Select row to setup the item store and reload the data.

func pickerView(pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
    if pickerView == countryPicker {
        switch row {
        case 0:
            selectedItemsArray = usItems
        case 1:
            selectedItemsArray = euItems
        case 2:
            selectedItemsArray = jpItems
        default:
            selectedItemsArray = []  
        }
        // IMPORTANT reload the data on the item picker
        itemPicker.reloadAllComponents()
    } else if pickerView == itemPicker {
        // Get the current item
        var item = selectedItemsArray[row]
        // Assign value to a label based on which array we are using
        if selectedItemsArray == usItems {
            usLabel.text = item
        } else if selectedItemsArray == euItems {
            euLabel.text = item
        } else if selectedItemsArray == jpItems {
            jpLabel.text = item
        }
    }
}

I haven't tested this code, but the logic should be correct.