Detect UILabel text change in swift

Question

Is there a way to get notified when there is a change in a UILabel\'s text or would I be better off using a UITextField with userInteractionE

Answer 1

Swift 5

If you want to observe text changes in the label and make an animation. You need to create subclass UILabel

class ObservedLabelAnimate: SpringLabel {

    override var text: String? {
        didSet {
            if let text = text {
                if oldValue != text {
                    animation = "fadeInLeft"
                    duration = 1.2
                    animate()
                }
                print("This is oldvalue \(oldValue), and this is the new one \(text)")
            }
        }
    }
}

for this example, I subclass 'SpringLabel' that inherits from UILabel

from https://github.com/MengTo/Spring

Basically it will check if the oldValue and text (new one) is different then the animation will be fired

To use:

@IBOutlet weak var label: ObservedLabelAnimate!

Answer 2

Create a class that inherits from UILabel. Such as:

class YourLabel: UILabel {

    override var text: String? {
        didSet {
            if let text = text {
                println("Text changed.")
            } else {
                println("Text not changed.")
            }
        }
    }
}

Create a outlet of this class for your object.

@IBOutlet weak var label: YourLabel!
label.text = "abc"

Answer 3

You can do this simply with a subclass of UILabel:

class Label : UILabel {
    override var text: String? {
        didSet {
            print("Text changed from \(oldValue) to \(text)")
        }
    }
}

oldValue is a special value provided by Swift. See Property Observers

Answer 4

For Swift 3.2 and later, the preferred method is to use a closure-based observer:

@IBOutlet public weak var label: UILabel!

var textObserver: NSKeyValueObservation?

func someAppropriateFunction() {
  ...
  textObserver = label.observe(\.text) { [weak self] (label, observedChange) in
    self?.updateStuff()
  }
}

The closure will pass you the label instance and an NSKeyValueObservedChange that includes the following properties:

  indexes: IndexSet?
  isPrior: Bool
  kind: NSKeyValueObservedChange<Value>.Kind
  newValue: Value?
  oldValue: Value?

Answer 5

Swift 3

First, add an observer to UILabel for key path text.

label.addObserver(self, forKeyPath: "text", options: [.old, .new], context: nil)

Then

override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
  if keyPath == "text" {
    print("old:", change?[.oldKey])
    print("new:", change?[.newKey])
  }
}

Swift 2

label.addObserver(self, forKeyPath: "text", options: [.Old, .New], context: nil)

Then

override func observeValueForKeyPath(keyPath: String?, ofObject object: AnyObject?, change: [String : AnyObject]?, context: UnsafeMutablePointer<Void>) {
    if keyPath == "text" {
        print("old:", change["old"])
        print("new:", change["new"])
    }
}

Console Output

For example console would be:

old: Optional(<null>)
new: Optional(ABC)