Proximity state not changing after receiving notification - ios

Question

I am having a problem with the proximity sensor on the iPhone. It seems that when the idle timer is disabled and the proximity monitoring is enabled the screen (sometimes) will turn on when receiving a notification. After this the proximity state is reported incorrectly and the screen won't turn off again.
I provided a sample project to illustrate the problem. But the steps to reproduce are quite simple. I tested this on multiple phones (4S, 5, 6, 6+) with multiple iOS versions (7.0.3 and 8.3). It seems to occur most reliably when the phone is not connected to a power source or debugger.
The code in my only ViewController is (the view is created in a storyboard):
import UIKit
class ViewController: UIViewController {
#IBOutlet weak var checkingToggleButton: UIButton!
#IBOutlet weak var debugLabel: UILabel!
#IBOutlet weak var screenDebugLabel: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
self.checkingToggleButton.setTitle("Start checking", forState: UIControlState.Normal)
self.debugLabel.text = "Not checking"
NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("proximityChanged:"), name: "UIDeviceProximityStateDidChangeNotification", object: nil)
}
#IBAction func handleCheckingToggle(sender: AnyObject) {
let enabled = !UIDevice.currentDevice().proximityMonitoringEnabled
if enabled {
self.debugLabel.text = "Checking"
self.checkingToggleButton.setTitle("Stop checking", forState: UIControlState.Normal)
} else {
self.debugLabel.text = "Not checking"
self.checkingToggleButton.setTitle("Start checking", forState: UIControlState.Normal)
}
UIApplication.sharedApplication().idleTimerDisabled = enabled
UIDevice.currentDevice().proximityMonitoringEnabled = enabled
}
func proximityChanged(notification:NSNotification)
{
if UIDevice.currentDevice().proximityState{
self.screenDebugLabel.text = "Proximity true"
println("Proximity true")
} else {
self.screenDebugLabel.text = "Proximity false"
println("Proximity false")
}
}
}
Steps to reproduce:
Build the provided sample project on a device and run the App on the the device disconnected from power and the debugger (this seems to make some difference).
Enable proximityMonitoring and disable the idle timer by pressing the "Start checking" button.
Cover the proximity sensor, this turns the screen off.
Wait approximately 2 minutes (this also makes a difference, doing it too soon won't reproduce the problem)
Send yourself a notification (for instance an iMessage)
The screen will turn on and won't turn off again. We also created a label that shows the current proximityState, the state is (incorrectly) reported as false.
Link to sample project on GitHub:
https://github.com/TimPelgrim/ProximityTest

Answer 1

I've tested a lot of things with the Notification method.
As Asi mentioned it, it doesn't work well. The solution is to observe the variable.
The issue is still there in iOS 11.4.1 (not tested on iOS 12 beta yet).
Swift 4:
// Prepare you observer variable
private var observer: NSKeyValueObservation?
// ...
// Start observing proximityState
self.observer = UIDevice.current.observe(\.proximityState) { [weak self] (device, _) in
print("State changed: \("device.proximityState")")
}
// ...
// Don't forget to call the `invalidate` method on your observer when you want to stop observing
self.observer?.invalidate()

Answer 2

I sent in a technical support issue to the apple engineers and they told me this is a bug in the operating system. No report on when it gets fixed but be advised that this issue seems to be occur in all versions of (at least) iOS 7 and 8 and that there does not seem to be a workaround. I will update here if I receive notice of a fix.

Answer 3

There is actually workaround..
UIDevice.current.proximityState is changing as it should change. but the problem is with the UIDeviceProximityStateDidChange notification.
So the workaround is to create timer that check every x time if UIDevice.current.proximityState changed and that it. just don't use UIDeviceProximityStateDidChange.