swift - How to set UIStepper value from another class? - ios

Question

I have a tableview contains some tableviewcell with UIStepper. This is tableviewcell code:
class ShoppingCartItemCell: UITableViewCell {
static let reuseIdentifier = "ShoppingCartItemCell"
#IBOutlet weak var itemImage: UIImageView!
#IBOutlet weak var itemNameLabel: UILabel!
#IBOutlet weak var itemProviderLabel: UILabel!
#IBOutlet weak var itemPriceLabel: UILabel!
#IBOutlet weak var itemQuantityText: UITextField!
#IBOutlet weak var quantityStepper: UIStepper!
var oldValue = 0.0
var itemName = "" {
didSet {
itemNameLabel.text = itemName
}
}
var itemProvider = "" {
didSet {
itemProviderLabel.text = itemProvider
}
}
var itemPrice = "" {
didSet {
itemPriceLabel.text = itemPrice
}
}
var itemQuantity = "" {
didSet {
itemQuantityText.text = itemQuantity
}
}
}
And this is uistepper code in tableview:
class ShoppingCartViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {
#IBOutlet weak var tableView: UITableView!
#IBAction func quantityStepper(_ sender: UIStepper) {
ShoppingCartItemCell.itemQuantity = "\(Int(sender.value))"// this way is not possible...
// How to update the quantityStepper value in ShoppingCartItemCell class here
}
}
How to update the quantityStepper value in ShoppingCartViewController class? Some people will tell me to create #IBAction of quantityStepper in ShoppingCartItemCell class but my business logic must to do this way. Please help. Thanks all.

Answer 1

I highly recommend to use Key-Value Observation in Swift 4, it's very easy to implement
In the cell create a NSKeyValueObservation property
var observation : NSKeyValueObservation?
In the view controller in cellForRowAt set the values for stepper and label add the observer
let item = dataSource[indexPath.row] // assuming `dataSource` is the data source array
cell.quantityStepper.value = item.quantity
cell.itemQuantityText.text = "\(item.quantity)"
cell.observation = cell.quantityStepper.observe(\.value, options: [.new]) { (stepper, change) in
cell.itemQuantityText.text = "\(change.newValue!)"
// update the data model for example
item.quantity = change.newValue!
}
Finally you have to remove the observer in didEndDisplaying after the cell has left the screen.
func tableView(_ tableView: UITableView, didEndDisplaying cell: UITableViewCell, forRowAt indexPath: IndexPath) {
(cell as! ShoppingCartItemCell).observation = nil
}
No IBAction, no protocol / delegate. It's very simple and efficient.