How can I pause a Timer being used in SwiftUI? - swiftui

Question

I have this function that changes the centerLocation of the map, this causes the map to animate over all the locations. The lat and longitude are being incremented and decremented and repeats with the use of a timer. However I am currently trying to pause the timer. I have tried multiple methods and can't seem to get the timer to pause for a few seconds and resume. The only thing that works is using sleep, but that causes the whole UI to pause. This 'move' function is updating an #State CLLocationCoordinate's lat and long. This method is called in .onAppear().
timer.fire() does not work
I also tried something like this:
timer.invalidate()
DispatchQueue.main.asyncAfter(deadline: .now() + 5.00) {
timer.fire()
}
Code above does not work
func moveRegion() {
var currentLatitude = region.center.latitude
var currentLongitude = region.center.longitude
let increment = 0.25
var southAmerica = false
var europe = false
var australia = false
var america = true
Timer.scheduledTimer(withTimeInterval: (1.0/30.0), repeats: true) { (timer) in
//AMERICA CORD 37.0000, -95.000
//MOVING TO SOUTH AMERICA
//SOUTH AMERICA CORD -33.000, -70.000
if (america == true && southAmerica == false && europe == false && australia == false){
if (currentLatitude <= -33.000 && currentLatitude >= 37.0000 || currentLongitude <= -70.0000 && currentLongitude >= -95.0000 || currentLongitude >= -101.69999999998991) {
currentLatitude -= increment
currentLatitude -= increment
currentLatitude -= increment
if currentLongitude < -70.00 {
currentLongitude += increment
}
}
if (currentLatitude == -38.15000000000002 || currentLatitude <= -38.150000000000006 && currentLongitude <= -69.95000000000142){
// sleep(5), works but pauses whole UI
timer.invalidate()
Timer.scheduledTimer(withTimeInterval: 5.0, repeats: false) { pauseTimer in
timer.fire()
print(timer.isValid)
}
southAmerica = true
australia = false
america = false
europe = false
}
}
//MOVING TO EUROPE
//Europe CORD 48.000, 15.000
//if (currentLongitude > -74.00 && currentLongitude < -4.00)
if (southAmerica == true && australia == false && america == false && europe == false ){
if (currentLatitude > -39.000 && currentLatitude < 55.000 || currentLongitude > -70.00 && currentLongitude < 16.000) {
currentLongitude += increment
currentLongitude += increment
currentLatitude += increment
currentLatitude += increment
}
if (currentLatitude >= 48.04999999999936 || currentLatitude == 48.04999999999937 && currentLongitude <= 16.249999999996835){
sleep(5)
europe = true
southAmerica = false
australia = false
america = false
}
}
//MOVING TO AUSTRALIA
//AUSTRALIA CORD -36.000, 133.000
if (europe == true && southAmerica == false && australia == false && america == false){
if (currentLongitude > 9.00 && currentLongitude < 133.000) {
currentLongitude += increment
currentLongitude += increment
currentLongitude += increment
}
if (currentLatitude >= -38.000 && currentLatitude <= 49.0000){
currentLatitude -= increment
currentLatitude -= increment
}
if (currentLatitude <= -37.05000000000008 && currentLongitude >= 132.04999999999274){
sleep(5)
australia = true
southAmerica = false
europe = false
america = false
}
}
//MOVING TO AMERIA
if (australia == true && southAmerica == false && america == false && europe == false){
if (currentLongitude < 179.55){
currentLongitude += increment
currentLongitude += increment
if (currentLongitude > 179.500){
currentLongitude = -179.000
}
}
if (currentLongitude > -95.100) {
currentLongitude += increment
currentLongitude += increment
}
if (currentLatitude >= -39.000 && currentLatitude <= 37.0000){
currentLatitude += increment
currentLatitude += increment
}
if (currentLatitude >= 37.04999999999998 && currentLongitude >= -95.100){
australia = false
southAmerica = false
europe = false
america = true
currentLatitude = 37.0000
currentLongitude = -95.000
sleep(5)
}
}
region.center.longitude = currentLongitude
region.center.latitude = currentLatitude
centerLocation.latitude = currentLatitude
centerLocation.longitude = currentLongitude
}
}
Then in the view
var body: some View {
SwiftUIMapView(centerLocation: $centerLocation)
.onAppear {
DispatchQueue.main.async {
moveRegion()
}
}
}
Here is the full code bellow:
import SwiftUI
import MapKit
struct MapView: View {
var timer = Timer()
//Start Location of the Map
#State var region = MKCoordinateRegion(
center: CLLocationCoordinate2D(latitude: 37.0000, longitude: -95.000),
span: MKCoordinateSpan(latitudeDelta: 40, longitudeDelta: 40)
)
#State var centerLocation = CLLocationCoordinate2D()
func moveRegion() {
var currentLatitude = region.center.latitude
var currentLongitude = region.center.longitude
let increment = 0.25
var southAmerica = false
var europe = false
var australia = false
var america = true
Timer.scheduledTimer(withTimeInterval: (1.0/30.0), repeats: true) { (timer) in
//AMERICA CORD 37.0000, -95.000
//MOVING TO SOUTH AMERICA
//SOUTH AMERICA CORD -33.000, -70.000
if (america == true && southAmerica == false && europe == false && australia == false){
if (currentLatitude <= -33.000 && currentLatitude >= 37.0000 || currentLongitude <= -70.0000 && currentLongitude >= -95.0000 || currentLongitude >= -101.69999999998991) {
currentLatitude -= increment
currentLatitude -= increment
currentLatitude -= increment
if currentLongitude < -70.00 {
currentLongitude += increment
}
}
if (currentLatitude == -38.15000000000002 || currentLatitude <= -38.150000000000006 && currentLongitude <= -69.95000000000142){
// sleep(5), works but pauses whole UI
timer.invalidate()
Timer.scheduledTimer(withTimeInterval: 5.0, repeats: false) { pauseTimer in
timer.fire()
print(timer.isValid)
}
southAmerica = true
australia = false
america = false
europe = false
}
}
//MOVING TO EUROPE
//Europe CORD 48.000, 15.000
//if (currentLongitude > -74.00 && currentLongitude < -4.00)
if (southAmerica == true && australia == false && america == false && europe == false ){
if (currentLatitude > -39.000 && currentLatitude < 55.000 || currentLongitude > -70.00 && currentLongitude < 16.000) {
currentLongitude += increment
currentLongitude += increment
currentLatitude += increment
currentLatitude += increment
}
if (currentLatitude >= 48.04999999999936 || currentLatitude == 48.04999999999937 && currentLongitude <= 16.249999999996835){
sleep(5)
europe = true
southAmerica = false
australia = false
america = false
}
}
//MOVING TO AUSTRALIA
//AUSTRALIA CORD -36.000, 133.000
if (europe == true && southAmerica == false && australia == false && america == false){
if (currentLongitude > 9.00 && currentLongitude < 133.000) {
currentLongitude += increment
currentLongitude += increment
currentLongitude += increment
}
if (currentLatitude >= -38.000 && currentLatitude <= 49.0000){
currentLatitude -= increment
currentLatitude -= increment
}
if (currentLatitude <= -37.05000000000008 && currentLongitude >= 132.04999999999274){
sleep(5)
australia = true
southAmerica = false
europe = false
america = false
}
}
//MOVING TO AMERIA
if (australia == true && southAmerica == false && america == false && europe == false){
if (currentLongitude < 179.55){
currentLongitude += increment
currentLongitude += increment
if (currentLongitude > 179.500){
currentLongitude = -179.000
}
}
if (currentLongitude > -95.100) {
currentLongitude += increment
currentLongitude += increment
}
if (currentLatitude >= -39.000 && currentLatitude <= 37.0000){
currentLatitude += increment
currentLatitude += increment
}
if (currentLatitude >= 37.04999999999998 && currentLongitude >= -95.100){
australia = false
southAmerica = false
europe = false
america = true
currentLatitude = 37.0000
currentLongitude = -95.000
sleep(5)
}
}
region.center.longitude = currentLongitude
region.center.latitude = currentLatitude
centerLocation.latitude = currentLatitude
centerLocation.longitude = currentLongitude
}
}
var body: some View {
SwiftUIMapView(centerLocation: $centerLocation)
.onAppear {
DispatchQueue.main.async {
moveRegion()
}
}
}
}
Any help is greatly appreciated thank you!

Answer 1

Using Timer for this and trying to invalidate, re-fire, etc is going to be difficult (or in fact, impossible -- Timer can't re-fire once it is invalidated). But, this seemed like a pretty good opportunity to user Timer in a publisher with Combine and then just give it some intervals to wait out -- the publisher still fires events, it just doesn't do anything with them until the next wait interval has been hit:
struct ContentView : View {
var body: some View {
MapView()
}
}
class LocationManager : ObservableObject {
#Published var centerLocation = CLLocationCoordinate2D()
#Published var region : MKCoordinateRegion
private var currentLatitude : CLLocationDegrees
private var currentLongitude : CLLocationDegrees
init() {
let region = MKCoordinateRegion(
center: CLLocationCoordinate2D(latitude: 37.0000, longitude: -95.000),
span: MKCoordinateSpan(latitudeDelta: 40, longitudeDelta: 40)
)
currentLatitude = region.center.latitude
currentLongitude = region.center.longitude
self.region = region
}
private var cancellable : AnyCancellable?
private var waitUntil : Date?
private var currentFireDate : Date = Date()
func start() {
cancellable = Timer.publish(every: (1.0/30.0), on: .main, in: .default)
.autoconnect()
.sink { val in
if let waitUntil = self.waitUntil {
if val < waitUntil {
return
} else {
self.waitUntil = nil
}
}
self.currentFireDate = val
self.moveRegion()
}
}
let increment = 0.25
var southAmerica = false
var europe = false
var australia = false
var america = true
func moveRegion() {
//AMERICA CORD 37.0000, -95.000
//MOVING TO SOUTH AMERICA
//SOUTH AMERICA CORD -33.000, -70.000
if (america == true && southAmerica == false && europe == false && australia == false){
if (currentLatitude <= -33.000 && currentLatitude >= 37.0000 || currentLongitude <= -70.0000 && currentLongitude >= -95.0000 || currentLongitude >= -101.69999999998991) {
currentLatitude -= increment
currentLatitude -= increment
currentLatitude -= increment
if currentLongitude < -70.00 {
currentLongitude += increment
}
}
if (currentLatitude == -38.15000000000002 || currentLatitude <= -38.150000000000006 && currentLongitude <= -69.95000000000142){
waitUntil = currentFireDate.addingTimeInterval(5.0)
southAmerica = true
australia = false
america = false
europe = false
}
}
//MOVING TO EUROPE
//Europe CORD 48.000, 15.000
//if (currentLongitude > -74.00 && currentLongitude < -4.00)
if (southAmerica == true && australia == false && america == false && europe == false ){
if (currentLatitude > -39.000 && currentLatitude < 55.000 || currentLongitude > -70.00 && currentLongitude < 16.000) {
currentLongitude += increment
currentLongitude += increment
currentLatitude += increment
currentLatitude += increment
}
if (currentLatitude >= 48.04999999999936 || currentLatitude == 48.04999999999937 && currentLongitude <= 16.249999999996835){
waitUntil = currentFireDate.addingTimeInterval(5.0)
europe = true
southAmerica = false
australia = false
america = false
}
}
//MOVING TO AUSTRALIA
//AUSTRALIA CORD -36.000, 133.000
if (europe == true && southAmerica == false && australia == false && america == false){
if (currentLongitude > 9.00 && currentLongitude < 133.000) {
currentLongitude += increment
currentLongitude += increment
currentLongitude += increment
}
if (currentLatitude >= -38.000 && currentLatitude <= 49.0000){
currentLatitude -= increment
currentLatitude -= increment
}
if (currentLatitude <= -37.05000000000008 && currentLongitude >= 132.04999999999274){
waitUntil = currentFireDate.addingTimeInterval(5.0)
australia = true
southAmerica = false
europe = false
america = false
}
}
//MOVING TO AMERIA
if (australia == true && southAmerica == false && america == false && europe == false){
if (currentLongitude < 179.55){
currentLongitude += increment
currentLongitude += increment
if (currentLongitude > 179.500){
currentLongitude = -179.000
}
}
if (currentLongitude > -95.100) {
currentLongitude += increment
currentLongitude += increment
}
if (currentLatitude >= -39.000 && currentLatitude <= 37.0000){
currentLatitude += increment
currentLatitude += increment
}
if (currentLatitude >= 37.04999999999998 && currentLongitude >= -95.100){
australia = false
southAmerica = false
europe = false
america = true
currentLatitude = 37.0000
currentLongitude = -95.000
waitUntil = currentFireDate.addingTimeInterval(5.0)
}
}
region.center.longitude = currentLongitude
region.center.latitude = currentLatitude
centerLocation.latitude = currentLatitude
centerLocation.longitude = currentLongitude
}
}
struct MapView: View {
#ObservedObject var locationManager = LocationManager()
var body: some View {
SwiftUIMapView(centerLocation: $locationManager.centerLocation)
.onAppear {
locationManager.start()
}
}
}
struct SwiftUIMapView : UIViewRepresentable {
#Binding var centerLocation : CLLocationCoordinate2D
func makeUIView(context: Context) -> MKMapView {
let mapView = MKMapView()
return mapView
}
func updateUIView(_ uiView: MKMapView, context: Context) {
uiView.centerCoordinate = centerLocation
}
}
Here's what happens:
Location is now controlled by an ObservableObject LocationManager
On start(), a publisher that fires once every 1/30 seconds is fired
On each fire, it calls moveLocation()
When moveLocation wants to pause, it sets waitUntil 5 seconds ahead of the last date of the publisher firing
If the the publisher gets fired and the time is before waitUntil, it just returns and waits for the next fire