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SOLVED: Day 28 - Challenge Three

Forums > 100 Days of SwiftUI


I have met with some problems when trying to keep recomended bed time always on the screen. I didn't know how to call calculateBedTime function automatcially when any settings are changed if calculate button removed. I have tried onAppear but it seemed to only work on the first appearance.

Could someone help me on this?


Hi @wctjerry,

it was a long time that I did this day so I had too look back what the challenge was 😛.

If I remember correctly the original project shown by Paul uses a button and when you press it, it will show the recommended bed time right?

Well if you want to automate this you just have to create a computed propterty with the name calculatedBedtime and the type String. A Computed property is always updated so you can just show that property inside a text block:

            Section(header: Text("Recommended Bedtime")) {

The computed property I used is shown below but you might have to adjust it to your needs.

var calculatedBedtime: String {
    let model = SleepCalculator()

    let components = Calendar.current.dateComponents([.hour, .minute], from: wakeUp)
    let hour = (components.hour ?? 0) * 60 * 60
    let minute = (components.minute ?? 0) * 60
    var bedTime = "Please set all input values"

    do {
        let prediction = try model.prediction(wake: Double(hour + minute), estimatedSleep: sleepAmount, coffee: Double(coffeeAmount))
        let sleepTime = wakeUp - prediction.actualSleep

        let formatter = DateFormatter()
        formatter.timeStyle = .short
        bedTime = formatter.string(from: sleepTime)
    } catch {
        alertTitle = "Error"
        alertMessage = "Sorry, there was a problem calculating your bedtime."
        showingAlert = true

    return bedTime

I hope this helps you further?


A Computed property is always updated so you can just show that property inside a text block:

Thank you @@nicolinden , I didn't notice this way to use computed property. That works perfectly!


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