A few months ago, Apple removed my app Interval RunCalc from the App Store for being too old and not updated. In this series of articles I’ll document what I did on rebuilding and improving the app. In the last installment, I built a very flexible UIPickerView into my app for fast but reliable data entry. Now I have to hook up that picker view to my app, and build the first round of user interfaces, along the way finding I’ve painted myself into a corner a few times and made several really silly mistakes.

Back in the first installment in this series, I did a few sketches of what I wanted for the user interface. My final sketch was this:

After I made that sketch, I realized something I forgot. I’ll need a way to change units. I also want a better solution to locking one of the variables to be my result. In sketch above, that feature is scribbled in the margin. To change units, I made a button that displays units. Tapping it would give a selection of units.

I removed two of my five entries on the top, Speed and Repetition. I dropped the repetition feature completely. While writing the model, pace and speed became the same, just with different units. That left the three parts on top, a table for the intervals below it and a toolbar. I cleaned it up to look like this:

I liked the look of this, so I went to Xcode, deleted the controls on the storyboard I was using for testing and designed this:

I kept to a very simple palette. The three rows on top are UIViews, labeled Time, Pace and Speed. Each row has two or three buttons as subviews.

Using auto layout, I aligned the baselines of the of the Units  buttons( the one marked m) and Entry buttons( the one marked Distance), and aligned the Entry vertically to the view, The lock button was pinned up, down and left to 0 and I made the width of the lock button 10% the width of the view. If you need a refresher on auto layout, Check out my book Practical Autolayout for Xcode 8

I can pin all the elements where I want them. This keeps everything modular, and with no extra effort I have a landscape layout, something I never had in the original app.

In a later installment, I’ll use class sizes to make a different layout for iPad.
The lighter center section is a UIView which I use as a container view for my interval table. On the bottom is a space for the toolbar, which is not a real toolbar, but a UIView I’ll once again add buttons to. A UIView with buttons for subviews gives me greater control of the buttons than I get with a toolbar.

Once I have this on a storyboard and all my constraints in place, I add outlets and actions for all the buttons. I’m ready to code.

The Lock Button

I designed the app to input data on two of the three rows, and get a result on the third. To indicate what row will get the result, I’ll use a lock button that toggles between the rows. The selected lock button is bright yellow, the deselected buttons a dark transparent yellow. I’ll add two constants for that

let lockOffColor = UIColor(red: 1.0, green: 1.0, blue: 0.31, alpha: 0.3)
let lockOnColor = UIColor(red: 1.0, green: 1.0, blue: 0.0, alpha: 0.9)

At the press of a lock button, I set the property in the model locked to the locked value, I turn on the touched button to glow yellow, and dim the other two buttons.

@IBAction func lockTime(_ sender: UIButton) {
runStats.locked = .time
timeLock.backgroundColor = lockOnColor
distanceLock.backgroundColor = lockOffColor
paceLock.backgroundColor = lockOffColor
}
@IBAction func lockDistance(_ sender: UIButton) {
runStats.locked = .distance
timeLock.backgroundColor = lockOffColor
distanceLock.backgroundColor = lockOnColor
paceLock.backgroundColor = lockOffColor

}
@IBAction func lockPace(_ sender: UIButton) {
runStats.locked = .pace
timeLock.backgroundColor = lockOffColor
distanceLock.backgroundColor = lockOffColor
paceLock.backgroundColor = lockOnColor

}

This is purely cosmetic. Figuring out what I’ll do with the lock will come later.

Setting the Unit of Measure

Each row has a unit of measure. The time row has no change of units, but the user can change the units for distance and pace. For changeable units, the button’s action will present a UIAlertController as an action sheet with possible units of measure. That will change the title of the button with the units measurement on it. Each unit of measure is a UIAlertAction with a closure. Here the distance action sheet code selecting miles and kilometers :

@IBAction func changeDistanceUnits(_ sender: UIButton) {
let actionSheet = UIAlertController(title: "Distance Units", message: "Select distance units", preferredStyle: .actionSheet)
let kilometers = UIAlertAction(title: "Kilometers", style: .default) { (alertAction) in
self.distanceUnits.setTitle("Km", for: .normal)
}
let miles = UIAlertAction(title: "Miles", style: .default) { (alertAction) in
self.distanceUnits.setTitle("Mi", for: .normal)
}
actionSheet.addAction(kilometers)
actionSheet.addAction(miles)
present(actionSheet, animated: true, completion: nil)
}

I start to get a sinking feeling here, one I had when finishing the picker as well. In version 1.0 the unit conversions were the biggest problem, and I’m beginning to wonder if they will be here too. There is nowhere in the model or controller to select the unit for distance or pace.

Opening the Entry Pickers

I’ll put that aside for the moment. Instead I’ll set up the actions for the three input buttons. In the last installment I went through the testing of a picker, and I copy that code to call the picker view as a modal. This time I’ll use a cross dissolve for the transition:

@IBAction func timerEntry(_ sender: UIButton) {
if runStats.locked != .time{
let vc = storyboard?.instantiateViewController(withIdentifier: "InputController") as! PickerViewController
vc.delegate = self
vc.units = .hoursMinutesSecond
vc.value = 4283.0 // in seconds 3600 + 600 + 60 + 20 + 3 = 1 hr 11min 23sec
vc.modalTransitionStyle = .crossDissolve
present(vc, animated: true, completion: nil)
}
}

I’m leaving the literal data in the action for now, so I’m testing known data. I’ll do similar for the distance and pace entry actions.

The Container View Table

Before I test, I want to add a little bit of code to the interval table view. I’ll implement the intervals after I get the basic app working. I’ll put some dummy data so I can look at the full User Interface. This is in a container view, a great way of getting a table view controller on a part of the superview without it using the complete view. I wrote about this more here if you are interested in the details. In short, I dragged a table view controller to the storyboard, and control-dragged from the UIView to the table view controller, selecting the Embed segue. That creates a relationship between controllers, which you see in the table view controller resizing to the size of the view.

I make a new UIViewController file. I tend not to use the UITableviewController template, since it has way too much junk in it. Instead I change the subclass UIViewController to UITableViewController.

class IntervalTableViewController: UITableViewController

Once I have this file made, I’ll use the identity inspector to set it as the class of the table view controller.

For the table view data sources I give one section and ten rows.

override func numberOfSections(in tableView: UITableView) -> Int {
return 1
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return 10
}

For the cells I print the row number with alternating colors.

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
let row = indexPath.row
if (row % 2) == 0{
cell.backgroundColor = UIColor.blue
} else {
cell.backgroundColor = UIColor.white
}
cell.textLabel?.text = " Row:\(row)"
return cell
}

I’ll add a title to the one section I have.

override func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
return "Intervals"
}

The table will show up for placement, but I’ll do nothing with it in this installment. I want calculations working first.

The First Iteration Test

I’m ready for my first test. Running the app gets me this:

The table is in place and the app looks nice and clean. Tapping the m/s for meters per second, opens up a action sheet.

Tapping Miles per Hour gets me mile per hour

If I tap Time, nothing happens. That’s the lock in action. But If I tap speed, the pickers show, with the correct value.

I lock speed

and try the time:

I can send data to the pickers.

 

Matching Colors in the Picker

I’m not happy about the colors. The pickers don’t match the rest of the app. I’d like the pickers to reflect the colors of the RootViewController without me playing around too much. If I change the root’s colors later on, the colors should still match.

I set up PickerViewController for background color property observers.

var backgroundColor = UIColor.darkGray{
didSet{
view.backgroundColor = backgroundColor
}
}
var toolBarColor = UIColor.lightGray{
didSet{
toolBar.backgroundColor = toolBarColor
}
}

In RootViewController, I assign the view’s background color to the PickerViewController’s background color.

@IBAction func timerEntry(_ sender: UIButton) {
if runStats.locked != .time{
let vc = storyboard?.instantiateViewController(withIdentifier: "InputController") as! PickerViewController
vc.units = .hoursMinutesSecond
vc.value = 4283.0 // in seconds 3600 + 600 + 60 + 20 + 3 = 1 hr 11min 23sec
vc.modalTransitionStyle = .crossDissolve
present(vc, animated: true, completion: nil)
vc.backgroundColor = view.backgroundColor!
}
}

When I change the property backgroundColor in the picker it should change the color in the picker. I try it and still get bright backgrounds, not dark ones. I forgot to take out test code. In the PickerViewController class, I have these three functions:

func distance(){
titleLabel.text = "Distance"
backgroundColor = UIColor.cyan
}
func paceOrSpeed(){
titleLabel.text = "Pace / Speed"
backgroundColor = UIColor.yellow
}
func time(){
titleLabel.text = "Time"
backgroundColor = UIColor.green
}

I comment out those background colors and run again. The background appears.

I see two more changes. I want to change the toolbar color to the button’s color. If I change the toolbar at top to the same color as the button’s background with this:

vc.toolBarColor = sender.backgroundColor!

It fails with an unexpectedly found nil while unwrapping an Optional value error. I know what’s wrong almost immediately. This is one of those silly mistakes, but one that is so subtle it could take a long time to find it. I’m relieved I found it early. The background isn’t in the button, but in the superview of the button. The button background is transparent, hence the nil. It should be this:

vc.toolBarColor = (sender.superview?.backgroundColor!)!

That works, but the result is worse for the text. Black on dark just doesn’t work.

I’m a little nervous about all those optionals and want a function to set the the text color. I add this to clean it all up.

func colors(picker:PickerViewController, from button:UIButton){
    if let backgroundColor = view.backgroundColor{
    picker.backgroundColor = backgroundColor
}
     if let toolBarColor = button.superview?.backgroundColor{
     picker.toolBarColor = toolBarColor
}
}

I replace the lines changing color in the actions with the colors method.

colors(picker: vc, from: sender)

My foreground text solution will go in the colors function. The color I’ll choose is the same as a title color, so I can start like this:

if let titleColor = button.titleColor(for: .normal){
}

Then I get stuck. I forgot to add a foreground color property to PickerViewController. The UIPickerView in the controller also does not have a foreground color property to set. Originally, I used the easiest of the UIPickerViewDatasource methods to display a picker component pickerView:titleForRow:forComponent. That returns a string. There’s a delegate method to return a UIView, such as a UILabel in whatever color or font I want:

func pickerView(_ pickerView: UIPickerView, viewForRow row: Int, forComponent component: Int, reusing view: UIView?) -> UIView {
    let label = UILabel()
    label.font = UIFont.preferredFont(forTextStyle: .title1)
    label.textColor = textColor
    switch components[component]{
    case .ten:
        label.text = String(format: "%01i", row)
    case .six:
        label.text = String(format: "%01i", row)
    case .colon:
        label.text = ":"
    case .decimal:
        label.text = "."
    }
    return label
}

I used a property textColor which I have yet to define. I’ll use a property observer to change all the other text on the picker controller to this color.

var textColor = UIColor.black{
    didSet{
        backButton.setTitleColor(textColor, for: .normal)
        doneButton.setTitleColor(textColor, for: .normal)
        titleLabel.textColor = textColor
        unitsOfMeasureLabel.textColor = textColor
}
}

Back in RootViewController, the colors method changes to:

func colors(picker:PickerViewController, from button:UIButton){
     if let backgroundColor = view.backgroundColor{
         picker.backgroundColor = backgroundColor
}
     if let toolBarColor = button.superview?.backgroundColor{
         picker.toolBarColor = toolBarColor
}
     if let titleColor = button.titleColor(for: .normal){
         picker.textColor = titleColor

}
}

Now I reflect the colors in my buttons in the picker, giving a consistent and readable look:

The title should read Distance, not 583.0 . That’s a testing element I left in the title, which I comment out.

func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
updatePickerValue()
//titleLabel.text = "\(value)" //for testing only
}

Delegation From the Picker

I’ll send data from the picker to the root via delegation. I’ll add to PickerViewController.swift a protocol for a delegate:

protocol PickerViewControllerDelegate{
func pickerDidFinish(value:Double, controller:PickerViewController)
}

I’ll go through all the normal steps for making a delegate. If you don’t know those I’d suggest my LinkedInLearning course on delegation and datasources. The last of those steps is adding the delegate method to RootViewController.

func pickerDidFinish(value: Double, controller: PickerViewController) {
}

I’ve been ignoring an important question: value is a Double, but what does it measure? What’s the units? How do I reflect that in the user interface?

I designed PickerViewController with an enum for that.

enum Units {
        case meters,kilometers,miles //distance
        case milesPerHour,minutesSecondsPerMile,kilometersPerHour // speed and pace
        case hoursMinutesSecond //time
    }
}

I set up a switch clause, and assign value to the right place in the right unit system…well almost.

func pickerDidFinish(value: Double, controller: PickerViewController) {
    switch controller.units {
    case .meters:
        runStats.distance.meters(value)
    case .kilometers:
        runStats.distance.kilometers(value)
    case .miles:
        runStats.distance.miles(value)
    case .hoursMinutesSecond:
        runStats.time.seconds(value)
    case .kilometersPerHour:
        runStats.pace.kilometersPerHour(value)
    case .milesPerHour:
        runStats.pace.milesPerHour(value)
    case .minutesSecondsPerMile:
        //ummmmm.......not there!!!
    }
}

I need one more conversion setter I didn’t originally have in PaceStats. for .minutesSecondsPerMile going to the picker, I have seconds per mile coming back out, but no method to change and store that as meters per second. I did the calculations and included it as part of the minutes and seconds getter:

public func minutes(_ minutes:Int,seconds:Int){
let secondsPerMile = Double(60 * minutes + seconds)
paceStat = 1609.344 / secondsPerMile
}

I can break this up to

func secondsPerMile(_ secondsPerMile:Double){
paceStat = 1609.344 / secondsPerMile
}
public func minutes(_ minutes:Int,seconds:Int){
secondsPerMile(Double(60 * minutes + seconds))
}

then finish the delegate method with

case .minutesSecondsPerMile:
runStats.pace.secondsPerMile(value)

Display Updates

I returned data from the picker and changed the model. Next I’ll update the root view’s display with new values. I’ll start a new method and add this for the time using the hourMinutesSeconds function of TimeStat

func updateDisplay(){
//time
    let timeTitle = "Time: " + runStats.time.hoursMinutesSeconds()
    timeEntry.setTitle(timeTitle, for: .normal)
}

For distance, I have meters, kilometers and miles. Which one do I display? I have no idea and the model doesn’t either. I’ll have to add tracking of this. I can track this in the model or in the controller. I go for the model. I’ll add an enumeration, a property using that enumeration, and a method that returns a formatted string based on that property.

I’ll try this first with the simpler DistanceStat. The enum for distance DisplayUnits would be kilometers and miles, which I add to a property displayUnits.

enum DisplayUnits {
    case kilometers,miles
}
var displayUnits:DisplayUnits = .miles

To my getters, I add the method

func displayString()->String{
    let string = "Distance: %7.1"
    switch displayUnits {
    case .miles:
         return String(format:string, miles())
    case .kilometers:
        return String(format:string, kilometers())
}

}

With a model that tracks the units I’m using, I set displayUnits in the action sheets’ alert actions I set up earlier. I’ll also update the display when I change units. For distance’s kilometer Alert Action it would look like this:

let kilometers = UIAlertAction(title: "Kilometers", style: .default) { (alertAction) in
self.distanceUnits.setTitle("Km", for: .normal)
self.runStats.distance.displayUnits = .kilometers
self.updateDisplay()
}

Miles would follow the same pattern. I‘ll set the distanceEntry button title in updateDisplay to

distanceEntry.setTitle(runStats.distance.displayString(), for: .normal)

In distanceEntry, I’ll set vc to 5 kilometers as the initial value. I’ll hit run and get 5 kilometers.

I’ll change that to 8 and press Done. Nothing happens. That’s because I forgot to add update to the delegate method. I did add it to the units, so I’ll change to Kilometers and get 7, which is the wrong answer.

I change to Miles and also get 7.

Checking my code I find a seriously stupid error.

let string = "Distance: %7.1”

I forgot an f. It should be %7.1f. I add updateDisplay to the delegate method too. I try again. And this time it works. For kilometers I get 5.0 and for miles 3.11.

I’ll do the same thing for the pace, now that I know this works. The only variation is distinguishing between speed and pace, which I do in updateDisplay.

var paceTitle = runStats.distance.displayString()
if runStats.pace.displayUnits == .minutesSecondsPerMile{
    paceTitle = "Pace: " + paceTitle
} else {
    paceTitle = "Speed: " + paceTitle
}
paceEntry.setTitle(paceTitle, for: .normal)

I try that out in the simulator, and it fails, reading zero. The picker reads correctly as 11:23 min/mi and the speed/pace label changes correctly. Changing the units always reads zero. I add to the delegate method a print(value) to check if the value gets there, and it does. Still in the delegate method I try to see if the displayString() works right, and it does. The problem is in updateDisplay, and once again it’s a typo. I had runStats.distance instead of runStats.pace.

I try it one more time, And this time it works.

I’ve connected all the user interface elements to the controller. Along the way, I made several silly mistakes, which can and will happen to anyone writing code. Its silly mistakes like these that make the most bugs. I also gained a greater appreciation for enum and switch, which are doing an incredibly good job of keeping my units straight. I have a consistent user interface, one that I find streamlined and elegant, at least compared to version 1.0. I have a lot to go though. In the next installment, I’ll hookup the model to the entry buttons, and start calculating run stats.

In an earlier post, I discussed the repeating local notifications in the UserNotification framework, but that discussion misses one detail: repeating notifications less than 60 seconds. The framework will very stubbornly refuse to have a repeating notification less than a minute, giving a runtime error if you do.

In my LinkedInLearning course Learning iOS Notifications, I mentioned a workaround to get around this problem, but didn’t show how to in that course. Today, I’ll show you how to get repeating notifications for times less than 30 seconds.

Before I do, I will give a big warning from the user experience perspective. Rapid-fire notifications are annoying to the user under most circumstances. Don’t do this unless the functionality of the application is such that the user needs the frequent interruptions. Almost all the cases I can think of  are interval timers.

In fitness,  interval training is a recommended training regimen with lots of benefits .  There’s even a movement  created by U.S. Olympian Jeff Galloway among distance runners  to do run/walk/run a interval-based distanced running strategy to reduce injury. There’s also speedwork intervals for runners. It’s here that you’ll often see those less than 60 second time intervals repeated. Often it will be 30 seconds of intense activity repeated with lesser activity for a rest period. In this lesson, We’ll set up a 30 second repeat timer to show you the workaround to the 60 second limitation.

I’m going to assume you have a good idea of how to use local notifications for this lesson. If you don’t, try this lesson first or even better take my video course Learning iOS Notifications on Lynda.com or LinkedInlearning.

Make a New Project

I’ve made a starting file for this lesson which you can download here: shortrepeat_start If making this yourself, Make a new single view project ShortRepeat.  When the project loads change the display name to Repeat 30s

Go to the storyboard. Drag out two buttons and a label. Title and arrange them like this:

You can leave this like this for this lesson if you want to code. I’ll clean them up in a little auto layout and color:

To see how I did this, you can download the start file. 

Open the assistant editor and add two actions to the code:

@IBAction func startButton(sender:UIButton) {
}
@IBAction func stopButton(sender:UIButton) {
}

Drag from the startButton‘s circle to the to the Start button. Drag from the stopButton‘s  circle to the Stop button.

You’re ready to code. You can download a starter version of this here: shortrepeat_start

Set Up a Notification

There’s a few steps we’ll need to set up before using a notification. Close the assistant editor and go to the ViewController class code. You’ll need to include the UserNotification framework first. Under import UIKit, add this

import UserNotifications

You’ll be using the user notification delegate too. Add its protocol to the class

class ViewController: UIViewController,UNUserNotificationCenterDelegate {

At the bottom of the class, add this to make the two delegates:

//MARK: - User Notification Center Delegates
    func userNotificationCenter(_ center: UNUserNotificationCenter, didReceive response: UNNotificationResponse, withCompletionHandler completionHandler: @escaping () -> Void) {
        completionHandler()
    }
    
    func userNotificationCenter(_ center: UNUserNotificationCenter, willPresent notification: UNNotification, withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) {
        completionHandler([.alert,.sound])
    }

The usernotificationCenter:willPresent notification method assures us that the notification will show up and sound the alert when we are viewing the application. We’ll use the usernotificationCenter:didRecieve response: a little later to code a stop action, but for now I added the required completion handler.

Go to ViewDidload to point the delegate to the delegate methods.

UNUserNotificationCenter.current().delegate = self

Notifications require user permission, so add this to viewDidLoad as well:

UNUserNotificationCenter.current().requestAuthorization(
    options: [.alert,.sound]) 
    {(granted, error) in
         self.isGrantedAccess = granted
    }

You’ll set the notification for alert and sound, and set a variable isGrantedAccess as a flag to decide if you have been granted access for notifications.

Of course you haven’t defined isGrantedAccess yet. Add it to the top of the class.

var isGrantedAccess = false

You’ll also need a category with a Stop button action for the notification. Add this to viewDidLoad

let stopAction = UNNotificationAction(identifier: "stop.action", title: "Stop", options: [])
        let timerCategory = UNNotificationCategory(identifier: "timer.category", actions: [stopAction], intentIdentifiers: [], options: [])
        UNUserNotificationCenter.current().setNotificationCategories([timerCategory])
        

This adds a stop action, which will display a stop button on the notification.

Making a Notification

We’ve done much of the setup, it’s time to make the notification. The secret to the notification is to make a time interval trigger of near zero, to launch an immediate notification. You’ll use a timer to send the notification.

Make a new function sendNotification. Add an if clause to check if we are granted access

func sendNotification(){
    if isGrantedAccess{
    }
}

In the if clause’s block, add some content:

let content = UNMutableNotificationContent()
content.title = "HIIT Timer"
content.body = "30 Seconds Elapsed"
content.sound = UNNotificationSound.default()
content.categoryIdentifier = "timer.category"

This will print a simple message and will play the default sound when 30 seconds is up. It also will use the timer.category to display buttons.

Next add the trigger. The strategy is to use a trigger at zero, but a timeInterval of zero is not allowed either. Use a time interval trigger set to a small interval such as 0.001, with no repeat to send one notification immediately.

let trigger = UNTimeIntervalNotificationTrigger(
    timeInterval: 0.001, repeats: false) //close to immediate as we can get. 

Finally make and add the notification request to the current user notification center. For error handling, I just print a message to the console.

        let request = UNNotificationRequest(identifier: "timer.request", content: content, trigger: trigger)
        UNUserNotificationCenter.current().add(request) { (error) in
            if let error = error{
                print("Error posting notification:\(error.localizedDescription)")
            }
        }

To test out this function, add it to the startButton method

@IBAction func startButton(_ sender: UIButton) {
        sendNotification()
    }

Build and Run. you’ll get the permissions alert:

Tap Allow.  Hit the Start button and you immediately get a notification

Repeat the Notification

I’ve gotten the notification to fire pretty close to immediately. Now I’ll add a timer to fire repeatedly every 10 seconds. Add to the top of the view controller class a timer

private var timer = Timer()

Code the following function to start a timer:

func startTimer(){
        let timeInterval = 10.0
        if isGrantedAccess && !timer.isValid { //allowed notification and timer off
            timer = Timer.scheduledTimer(withTimeInterval: timeInterval, repeats: true, block: { (timer) in
                self.sendNotification()
            })
        }
    }

For this code, I used the Timer initializer with a closure named block, instead of the one with a target. We have only one line of code to send the notification, to execute every time the timer completes an interval, so using a closure is more compact and easier to read than calling another function. I placed the timer’s start in a if clause to prevent the timer from starting if we don’t have permission for notifications and if the timer is already started. We don’t want to re-start the timer once started because that will mess up the intervals we are timing, and it is possible for someone working out to accidentally hit the Start button on their phone. I also set the time interval to a shorter ten seconds for testing purposes. I’ll move it back to 30  as shown in the notification when the app finishes testing.

Stopping the Notification

I’ll need to stop the notifications firing when I’m done with my workout. To do that, I’ll make another function to invalidate the timer. I’ll also clean out all the notifications

func stopTimer(){
    //shut down timer
    timer.invalidate()
    //clear out any pending and delivered notifications
    UNUserNotificationCenter.current().removeAllPendingNotificationRequests()
    UNUserNotificationCenter.current().removeAllDeliveredNotifications()
} 

There’s nothing useful about having a timer notifications floating around, so getting rid of them when you stop the timer makes things nice and tidy. There can be at most two here, because all pending notifications replace each other. Therefore you may have one pending notification, and very likely will have one delivered notification at most.

I’ll place the stopTimer method in two places. First, I’ll place it in the stopButton

@IBAction func stopButton(_ sender: UIButton) {
        stopTimer()
    }

Secondly, I’ll add it as the action for the stop.action on the notification. Drop down to the user notification center delegates at the bottom of your code and change the userNotificationCenter: didReceive response: to this:

func userNotificationCenter(_ center: UNUserNotificationCenter, 
    didReceive response: UNNotificationResponse, 
    withCompletionHandler completionHandler: @escaping () -> Void) {
        if response.actionIdentifier == "stop.action"{
            stopTimer()
        }
        completionHandler()
    }

Set your simulator device to an iPhone6. Phones later than this one use 3D touch in the simulator and you may not be able to get the action to appear otherwise with mice and older trackpads in the simulator. Build and run.

Unless you were using an iPhone 6 simulator earlier in this tutorial, the phone should boot and then ask permission again.

Select Allow, and then Start. Notifications will start to appear every ten seconds.

Press Stop The notifications stop. Press Start again and then Command-L to lock the phone. You’ll start to see notifications on the lock screen.

Swipe toward the left and you’ll see two buttons

Tap the View button.  You’ll see your notification and the action button. Tap Stop and the notifications stop.

Bonus:The Apple Watch and Repeat Notifications

The Stop action button is something you should definitely put into your application. On a long run, it takes a while to unlock the phone and hit Stop in the app.  Opening the notification is faster. There is the other place this notification might show up: An Apple Watch

Local phone notifications appear on an Apple watch paired to a phone that is locked or asleep. There may be a slight time delay, but they will show up. On a workout where you start your app, the phone will eventually lock during the workout.  The paired Apple watch will continue to get the notifications. Since we included sound as part of the content, that will mean the watch will include a haptic touch for the notification.

This method of repeat notification does have it limitations. It does run in the foreground and does use more processor time and power than the repeat notifications. You’ll need to set it up for background timing if you turn the app off or the device times out. If you do not have to do time intervals less than  60 seconds use the framework instead of this.

The Whole Code

You will find the complete project here: shortrepeat_end It includes some extra watchOS files and some graphics  to make the watch and project look a little nicer.

//
//  ViewController.swift
//  ShortRepeat
//
//  Created by Steven Lipton on 2/24/17.
//  Copyright © 2017 Steven Lipton. All rights reserved.
//

import UIKit
import UserNotifications

class ViewController: UIViewController,UNUserNotificationCenterDelegate {
    var isGrantedAccess = false
    private var timer = Timer()
    
    func startTimer(){
        let timeInterval = 30.0
        if isGrantedAccess && !timer.isValid { //allowed notification and timer off
            timer = Timer.scheduledTimer(withTimeInterval: timeInterval, repeats: true, block: { (timer) in
                self.sendNotification()
            })
        }
    }
    
    func stopTimer(){
        //shut down timer
        timer.invalidate()
        //clear out any pending and delivered notifications
        UNUserNotificationCenter.current().removeAllPendingNotificationRequests()
        UNUserNotificationCenter.current().removeAllDeliveredNotifications()
    }
    
    func sendNotification(){
        if isGrantedAccess{
            let content = UNMutableNotificationContent()
            content.title = "HIIT Timer"
            content.body = "30 Seconds Elapsed"
            content.sound = UNNotificationSound.default()
            content.categoryIdentifier = "timer.category"
        
            let trigger = UNTimeIntervalNotificationTrigger(timeInterval: 0.001, repeats: false)
            let request = UNNotificationRequest(identifier: "timer.request", content: content, trigger: trigger)
            UNUserNotificationCenter.current().add(request) { (error) in
                if let error = error{
                    print("Error posting notification:\(error.localizedDescription)")
                }
            }
        }
    }
    
    
    @IBAction func startButton(_ sender: UIButton) {
        startTimer()
    }
    @IBAction func stopButton(_ sender: UIButton) {
        stopTimer()
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        UNUserNotificationCenter.current().delegate = self
        UNUserNotificationCenter.current().requestAuthorization(options: [.alert,.sound]) { (granted, error) in
                self.isGrantedAccess = granted
        }
        let stopAction = UNNotificationAction(identifier: "stop.action", title: "Stop", options: [])
        let timerCategory = UNNotificationCategory(identifier: "timer.category", actions: [stopAction], intentIdentifiers: [], options: [])
        UNUserNotificationCenter.current().setNotificationCategories([timerCategory])
        
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
    
//MARK: - User Notification Center Delegates
    func userNotificationCenter(_ center: UNUserNotificationCenter, didReceive response: UNNotificationResponse, withCompletionHandler completionHandler: @escaping () -> Void) {
        if response.actionIdentifier == "stop.action"{
            stopTimer()
        }
        completionHandler()
    }
    
    func userNotificationCenter(_ center: UNUserNotificationCenter, willPresent notification: UNNotification, withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) {
        completionHandler([.alert,.sound])
    }

}