Detect UILabel text change in swift
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)
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"
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