Following is one of the easiest way to identify if the action performed over UIStepper, increments the value or decrements it!

Basic logic is to store the initial value in a variable and then comparing new value to the older one to identify & then modifying it on the go.



//Creating outlet for stepper
@IBOutlet weak var stepper : UIStepper!

//Declaring a variable to store initial value
var oldValue : String!

//assign the value of stepper to the variable when view loads
//put this in viewDidLoad method
oldValue = "\(stepper.value)"

//Now inside UIAction of stepper, create an if-else condition to compare! 
@IBAction func stepperValueChanged(_sender:Any)
{
   if (stepper.value > oldValue) //when oldValue is less than new value
   {
      //Implement something..
      oldValue += 1
      //Increment oldValue
   }
   else //anything other than above case
   {
     //Implement something..
     oldValue -= 1
     //decrement oldValue
   }
}