This seems to be a stupid question but I'm struggling to find an answer, here's part of my codes where user can update the count of any activity in the details view:

      Stepper("\(activity.count) \(activity.count <= 1 ? "time" : "times")", onIncrement: {
          newActivity.count += 1
          changeCount(for: activity, updatedActivity: newActivity)
      }, onDecrement: {
          newActivity.count -= 1
          changeCount(for: activity, updatedActivity: newActivity)
      })

My question is how can I prevent the stepper from going below 0? I want to specify a range but it does not allow me to add an "in: 0..." parameter to it.

It's not covered by the examples in the definition or have I missed it? Thanks for your help!

Your Stepper seems overly complicated, but maybe I'm not understanding what you're trying to do. Here's a simple Stepper that stays between 0 and 10:

struct ContentView: View {
    @State private var count = 0.0

    var body: some View {
        Form {
            Stepper("Count: \(count.formatted())", value: $count, in: 0...10, step: 0.25)
        }
    }
}

@vtabmow Thanks for your reply!

Actually I want to call the changeCount() function whenver user change the value of activity count using the stepper. This will change the value of newActivity.count while newActivity is a copy of the current activity struct instance, and will be used to replace it in the original activities array.

I think I just want to know if it's possible to specify the range like you do when closures like onIncrement / onDecrement are passed in, somehow like this:

Stepper(
  "<Text here>", 
  value: <$binding>, 
  in: <range>, 
  onIncrement: { 
   // Do something
      }, 
  onDecrement: {
   // Do something      
   })

If not then how should it be done?

You could try

First need a property to track count

@State private var oldCount = 0

then do this (where count is your activity.count)

Stepper("\(count)", value: $count, in: 0...10)
      .onAppear {
          oldCount = count
      }
      .onChange(of: count) { newCount in
            if newCount > oldCount {
                print("Increased Count - changeCount()")
            } else {
                print("Decreased Count - changeCount()")
            }
            oldCount = newCount
        }
      }

Or you can do

Stepper("\(count)") {
    if count <= 10 {
        count += 1
        print("Increased Count - changeCount()")
    } else {
        count = 10
    }
} onDecrement: {
    if count > 0 {
        count -= 1
        print("Decreased Count - changeCount()")
    } else {
        count = 0
    }
}

Part of the problem is that it seems you may want to use a one-sided range, at least judging by this:

I want to specify a range but it does not allow me to add an "in: 0..." parameter to it.

0... is a PartialRangeFrom. The Stepper initializers that accept an in parameter only take a ClosedRange (e.g., 0...10).

You can simulate a PartialRangeFrom like so:

Stepper("\(count)") {
    count += 1
} onDecrement: {
    count = max(0, count - 1)
}

Thanks you all for the advice, I get it now!