UIPickerView won't allow changing font name and size via delegate's `attributedTitleForRow...`

I have a another option may be it helpfull for you..

Do all work that need for normal picker view : for more help UIPickerView make in Swift iOS

Now follow this step : - you can use method of viewForRow like this

func pickerView(pickerView: UIPickerView, viewForRow row: Int, forComponent component: Int, reusingView view: UIView!) -> UIView
{
    var pickerLabel = UILabel()
    pickerLabel.textColor = UIColor.blackColor()
    pickerLabel.text = "PickerView Cell Title"
   // pickerLabel.font = UIFont(name: pickerLabel.font.fontName, size: 15)
    pickerLabel.font = UIFont(name: "Arial-BoldMT", size: 15) // In this use your custom font
    pickerLabel.textAlignment = NSTextAlignment.Center
    return pickerLabel
}

Updated Swift 3

func pickerView(pickerView: UIPickerView, viewForRow row: Int, forComponent component: Int, reusingView view: UIView!) -> UIView
{
    let pickerLabel = UILabel()
    pickerLabel.textColor = UIColor.black
    pickerLabel.text = "PickerView Cell Title"
    // pickerLabel.font = UIFont(name: pickerLabel.font.fontName, size: 15)
    pickerLabel.font = UIFont(name: "Arial-BoldMT", size: 15) // In this use your custom font
    pickerLabel.textAlignment = NSTextAlignment.center
    return pickerLabel
}

Updated Swift 5

func pickerView(_ pickerView: UIPickerView, viewForRow row: Int, forComponent component: Int, reusing view: UIView?) -> UIView
    {
        let pickerLabel = UILabel()
        pickerLabel.textColor = UIColor.white
        pickerLabel.text = "PickerView Cell Title"
        // pickerLabel.font = UIFont(name: pickerLabel.font.fontName, size: 15)
        pickerLabel.font = UIFont.boldSystemFont(ofSize: 20) // In this use your custom font
        pickerLabel.textAlignment = NSTextAlignment.center
        return pickerLabel
    }

May be it help full for you, I also used this in my project.

You can declare the datasource for pickerview

let arrDataSource:[String] = ["row 1","row 2","row 3"]

then use this array of string as title for row in below function

func pickerView(pickerView: UIPickerView, viewForRow row: Int, forComponent component: Int, reusingView view: UIView!) -> UIView

{
    let pickerLabel = UILabel()
    pickerLabel.textColor = UIColor.blackColor()
    pickerLabel.text = arrDataSource[row]
     pickerLabel.font = UIFont(name: pickerLabel.font.fontName, size: 15)
    //pickerLabel.font = UIFont(name: "Arial-BoldMT", size: 15) // In this use your custom font
    pickerLabel.textAlignment = NSTextAlignment.Center
    return pickerLabel
 }

SWIFT 3

func pickerView(_ pickerView: UIPickerView, viewForRow row: Int, forComponent component: Int, reusing view: UIView?) -> UIView {

    var string = ""

    let pickerLabel = UILabel()
    pickerLabel.textColor = UIColor.white
    pickerLabel.text = string
    pickerLabel.font = UIFont(name: "Rubik-Regular", size: 22) // In this use your custom font
    pickerLabel.textAlignment = .center

    return pickerLabel

}