Check out example codes for "change opacity of button clicked swift". It will help you in understanding the concepts better.

Code Example 1

@IBAction func keyPressed(_ sender: UIButton) {
  // sets opacity to half - you can change the opacity by editing "0.5"
  sender.alpha = 0.5
  
  /* 
  Code should execute after 0.2 second delay.
  You can change delay by editing 0.2.
  */
  DispatchQueue.main.asyncAfter(deadline: .now() + 0.2) {
    // Bring's sender's opacity back up to fully opaque
    sender.alpha = 1.0
  }
  
 }

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