swift-如何从另一个类设置UIStepper值? [英] swift - How to set UIStepper value from another class?

问题描述

我有一个tableview包含一些带有UIStepper的tableviewcell.这是tableviewcell代码:

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
    }
}
}

这是表格视图中的uistepper代码:

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
     }
}

如何更新ShoppingCartViewController类中的quantityStepper值?有人会告诉我在ShoppingCartItemCell类中创建quantityStepper的@IBAction，但是我的业务逻辑必须这样做.请帮忙.谢谢大家.

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.

推荐答案

我强烈建议在Swift 4中使用键值观察，这很容易实现

I highly recommend to use Key-Value Observation in Swift 4, it's very easy to implement

在单元格中创建一个NSKeyValueObservation属性

In the cell create a NSKeyValueObservation property

var observation : NSKeyValueObservation?

在cellForRowAt中的视图控制器中，为stepper设置值并为标签添加观察者

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!
}

最后，在单元格离开屏幕后，您必须在didEndDisplaying中删除观察者.

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
}

否IBAction，没有协议/委托.这是非常简单和高效的.

No IBAction, no protocol / delegate. It's very simple and efficient.

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