Update label.text at runtime

问题:

I try to make a label.text value get updated in a row of a table. The update is supposed to be triggered by a user entering a number in another textfield in this row:

My code looks like this:

Swift 3: ViewController

import UIKit

class RiskPlan: UIViewController, UITableViewDelegate, UITableViewDataSource {

    @IBOutlet weak var tableView: UITableView!
    var probability1 = String()
    var impact1 = String()
    var riskFactor = String()

    var result = Int()

func numberOfSections(in tableView: UITableView) -> Int {
        return 1
    }

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return 1
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = self.tableView!.dequeueReusableCell(withIdentifier: "Cell", for: indexPath) as! CellCustomized

    impact1 = (cell.impact?.text)!
    probability1 = (cell.probability?.text)!

    result = Int(impact1)! * Int(probability1)!
    cell.riskFactor?.text = String(result)

    self.tableView.reloadRows(at: [indexPath], with: UITableViewRowAnimation.top)

        return cell
    }
}

Swift 3: CellCustomized

import UIKit

class CellCustomized: UITableViewCell {

    @IBOutlet weak var probability: UITextField!
    @IBOutlet weak var impact: UITextField!
    @IBOutlet weak var riskFactor: UILabel!    

}

My problem is that

• self.tableView.reloadRows(at: [indexPath], with: UITableViewRowAnimation.top) does not do the update and
• I get a "fatal error: unexpectedly found nil while unwrapping an Optional value" for result = Int(impact1)! * Int(probability1)!

回答1:

If you want to know when changes are done in the textFields, func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell is not the place you want to put your calculation code.

Instead you should listen to the event .editingChanged on text fields from your CellCustomized class.

class RiskPlan: UIViewController, UITableViewDelegate, UITableViewDataSource {

  @IBOutlet weak var tableView: UITableView!

  func numberOfSections(in tableView: UITableView) -> Int {
    return 1
  }

  func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return 1
  }

  func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = self.tableView!.dequeueReusableCell(withIdentifier: "Cell", for: indexPath) as! CellCustomized

    return cell
  }
}

---

class CellCustomized: UITableViewCell {

  @IBOutlet weak var probability: UITextField!
  @IBOutlet weak var impact: UITextField!
  @IBOutlet weak var riskFactor: UILabel!

  var probability1 = 0
  var impact1 = 0

  override func awakeFromNib() {
    super.awakeFromNib()

    probability.addTarget(self, action: #selector(textOnTextFieldDidChange(textField:)), for: .editingChanged)
    impact.addTarget(self, action: #selector(textOnTextFieldDidChange(textField:)), for: .editingChanged)
  }

  func textOnTextFieldDidChange(textField: UITextField) {
    if textField === probability {
      probability1 = Int(textField.text!) ?? 0
    } else if textField === impact {
      impact1 = Int(textField.text!) ?? 0
    }

    riskFactor.text = String(probability1 * impact1)
  }

}

回答2:

If I'm not mistaking, you want to update the label's text depending on what you are inserting in the textfield(s).

In your CellCustomized you can do this:

class CellCustomized: UITableViewCell {

    // assuming that the outlets has been renamed...
    @IBOutlet weak var textField: UITextField!
    @IBOutlet weak var label: UILabel!

    override func awakeFromNib() {
        super.awakeFromNib()

        textField.addTarget(self, action: #selector(editing(sender:)), for: .editingChanged)
    }

    func editing(sender: UITextField) {
        // checking if the input is convertible to a number, and then add 5 for it (you can do your own operations)
        if let string = sender.text, Int(sender.text!) != nil {
            let int = Int(string)

            label.text = "\(int! + 5)"
        }
    }
}

hope that helped.