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SOLVED: Project 22 - blinking background color

Forums > 100 Days of Swift

In project 22, the background color is blinking between (any color) and grey if there is

else { update(distance: .unknown) }

In locationmanager(didrangebeacons) function.

If I remove the line it works alright.

import UIKit import CoreLocation

class ViewController: UIViewController, CLLocationManagerDelegate { var hasShownNotification = false

@IBOutlet weak var uuuidIdentifier: UILabel!
var uuids = [String]()

@IBOutlet weak var distanceReading: UILabel!
var locationManager: CLLocationManager?

override func viewDidLoad() {

    locationManager = CLLocationManager()
    locationManager?.delegate = self

    view.backgroundColor = .gray


func locationManager(_ manager: CLLocationManager, didChangeAuthorization status: CLAuthorizationStatus) {
    if status == .authorizedAlways {
        if CLLocationManager.isMonitoringAvailable(for: CLBeaconRegion.self) {
            if CLLocationManager.isRangingAvailable() {
                startScanning()                }

func startScanning() {

    uuids = ["5A4BCFCE-174E-4BAC-A814-092E77F6B7E5", "2F234454-CF6D-4A0F-ADF2-F4911BA9FFA6", "E2C56DB5-DFFB-48D2-B060-D0F5A71096E0"]

    for (number,uuidString) in uuids.enumerated() {
        let uuid = UUID(uuidString: uuidString)!
        let beaconIdentity = CLBeaconIdentityConstraint(uuid: uuid, major: 123, minor: 456)
        let beaconRegion = CLBeaconRegion(beaconIdentityConstraint: beaconIdentity, identifier: "MyBeacon\(number)")
        locationManager?.startMonitoring(for: beaconRegion)
        locationManager?.startRangingBeacons(satisfying: beaconIdentity)


func update(distance: CLProximity) {
    UIView.animate(withDuration: 1) {
        switch distance {
        case .far:
            self.view.backgroundColor = UIColor.blue
            self.distanceReading.text = "FAR"

        case .near:
            self.view.backgroundColor = UIColor.orange
            self.distanceReading.text = "NEAR"

        case .immediate:
            self.view.backgroundColor = UIColor.red
            self.distanceReading.text = "RIGHT HERE"
        case .unknown:
            self.view.backgroundColor = UIColor.gray
            self.distanceReading.text = "UNKNOWN"
            self.uuuidIdentifier.text = "UNKNOWN"

        @unknown default:
            self.view.backgroundColor = UIColor.red
            self.distanceReading.text = "UNKNOWN"
            self.uuuidIdentifier.text = "UNKNOWN"

func locationManager(_ manager: CLLocationManager, didRangeBeacons beacons: [CLBeacon], in region: CLBeaconRegion) {
    if let beacon = beacons.first {
        if hasShownNotification == false {
            hasShownNotification = true
            let ac = UIAlertController(title: "Beacon detected", message: "Beacon has been detected", preferredStyle: .alert)
            ac.addAction(UIAlertAction(title: "OK", style: .default))
            present(ac, animated: true)

        for uuid in uuids {
            if uuid == beacon.uuid.uuidString {
                self.uuuidIdentifier.text = uuid
                update(distance: beacon.proximity)

    else {
        update(distance: .unknown)



Is it possible that the function is called more often than the beacon is transmitting and that is the cause?


Hi @nyannyanrabu

Is it because you have more then one beacon that it trying to find. In the tutorial they is one one uuid where you have a Array of uuids


Thank you! I see it now!


Hi @nyannyanrabu ,

How did you manage to solve the blinking issue? It's occuring as I attempt Challenge 2 for this project, scanning for multiple beacons. Which I implemented in a very similar way to you (used an array).

Any help would be very beneficial, thank you!


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