Proximity State Not Changing After Receiving Notification

In this article, we will explore an issue with the proximity sensor in iOS devices that causes the screen to remain on after receiving a notification. We’ll delve into the problem, its causes, and provide a solution using Swift 4.

Understanding Proximity Monitoring

Proximity monitoring is a feature of the iPhone that detects when a user is holding their device against their ear or another object, typically to avoid displaying the screen during phone calls or other situations where it might be inconvenient. This feature can be enabled or disabled by an app, and it’s controlled through the proximityMonitoringEnabled property of UIDevice.

The proximityState property indicates whether the device is currently in a proximal state (i.e., close to the ear) or not. When this property changes, the UIDeviceProximityStateDidChangeNotification notification is sent to observers.

Problem Description

The problem at hand occurs when proximity monitoring is enabled, and the idle timer is disabled using UIApplication.sharedApplication().idleTimerDisabled = enabled. In such cases, if a notification is received while the device is in a proximal state (i.e., covered by the user’s hand), the screen will not turn off again. Instead, it remains on indefinitely.

Moreover, the proximity state reported after receiving the notification is incorrect, and it’s stuck at false.

Steps to Reproduce the Issue

To reproduce this issue, follow these steps:

Build a project that enables proximity monitoring and disables the idle timer.
Cover the proximity sensor while running the app on an unpowered and debugger-enabled device.
Wait for approximately 2 minutes.
Receive a notification (e.g., an iMessage).

After performing these steps, the screen will remain on, and the reported proximity state will be incorrect.

Solution

The solution to this issue lies in observing the proximityState property using NSKeyValueObservation. Here’s how you can do it:

Swift 4 Code Example

// Prepare your observer variable
private var observer: NSKeyValueObservation?

// ...

func viewDidLoad() {
    super.viewDidLoad()

    // Initialize the observer
    self.observer = UIDevice.current.observe(\.proximityState) { [weak self] (device, _) in
        print("State changed: \("device.proximityState")")
        
        // Update the screen debug label
        self.screenDebugLabel.text = "Proximity \(device.proximityState ? "true" : "false")"
    }
}

// ...

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
    
    // Update the observer when the proximity state changes
    self.observer?.invalidate()
}

// ...

By observing the proximityState property, we can update our view whenever it changes. This ensures that our screen debug label is always accurate and reflects the current proximity state.

In the handleCheckingToggle method, we invalidate the observer whenever the user enables or disables proximity monitoring. This prevents stale observations from causing issues.

Conclusion

The issue with the proximity sensor in iOS devices can be frustrating to deal with. However, by understanding how proximity monitoring works and using NSKeyValueObservation, you can create accurate and reliable applications that respond to changes in the device’s state.

In this article, we explored the problem of a proximal state not changing after receiving a notification. We also provided a solution using Swift 4 by observing the proximityState property. This approach ensures that our screen debug label is always up-to-date and reflects the current proximity state accurately.

By implementing these best practices in your own projects, you can create more reliable and accurate apps for iOS devices.

Table of Contents

Understanding Proximity Monitoring
Problem Description
Steps to Reproduce the Issue
Solution
- Swift 4 Code Example
  - Initializing the observer
  - Updating the screen debug label
  - Handling changes in proximity state
  - Invalidating the observer

Related Topics

Proximity monitoring in iOS devices
Using NSKeyValueObservation to observe device properties
Swift 4 best practices for app development

Last modified on 2025-02-02