In some cases, you want to show your users a UIPickerView with predefined contents for a UITextField instead of a keyboard.

Create a custom UIPickerView

At first, you need a custom wrapper-class for UIPickerView conforming to the protocols UIPickerViewDataSource and UIPickerViewDelegate.

class MyPickerView: UIPickerView, UIPickerViewDataSource, UIPickerViewDelegate

You need to implement the following methods for the DataSource and Delegate:

public func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
    if data != nil {
        return data!.count
    } else {
        return 0
    }
}

public func numberOfComponents(in pickerView: UIPickerView) -> Int {
    return 1
}

public func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
    if data != nil {
        return data![row]
    } else {
        return ""
    }
}

To handle the data, MyPickerView needs the properties data, selectedValue and textFieldBeingEdited:

/**
 The data for the `UIPickerViewDelegate`

 Always needs to be an array of `String`! The `UIPickerView` can ONLY display Strings
 */
public var data: [String]? {
    didSet {
        super.delegate = self
        super.dataSource = self
        self.reloadAllComponents()
    }
}

/**
 Stores the UITextField that is being edited at the moment
 */
public var textFieldBeingEdited: UITextField?

/**
 Get the selected Value of the picker
 */
public var selectedValue: String {
    get {
        if data != nil {
            return data![selectedRow(inComponent: 0)]
        } else {
            return ""
        }
    }
}

Prepare your ViewController

The ViewController that contains your textField, needs to have a property for your custom UIPickerView. (Assuming, that you already have another property or @IBOutlet containing your textField)

/**
 The picker view to present as keyboard
 */
var picker: MyPickerView?

In your viewDidLoad(), you need to initialize picker and configure it a bit:

picker = MyPickerView()
picker?.autoresizingMask = [.flexibleHeight, .flexibleWidth]
picker?.backgroundColor = UIColor.white()

picker?.data = ["One", "Two", "Three", "Four", "Five"] //The data shown in the picker

Now, you can add the MyPicker as inputView of your UITextField:

textField.inputView = picker

Dismissing the picker-keyboard

Now, you have replaced the keyboard by an UIPickerView, but there is no possibility to dismiss it. This can be done with a custom .inputAccessoryView:

Add the property pickerAccessory to your ViewController.

/**
 A toolbar to add to the keyboard when the `picker` is presented.
 */
var pickerAccessory: UIToolbar?

In viewDidLoad(), you need to create an UIToolbar for the inputAccessoryView: