Main Thread Checker: UI API called on a background thread: -[UIApplication applicationState]
SwiftGoogle MapsXcode9 BetaSwift Problem Overview
I am using google maps in Xcode 9 beta, iOS 11.
I am getting an error outputted to the log as follows:
> Main Thread Checker: UI API called on a background thread: -[UIApplication applicationState] PID: 4442, TID: 837820, Thread name: com.google.Maps.LabelingBehavior, Queue name: com.apple.root.default-qos.overcommit, QoS: 21
Why would this be occurring as I am almost certain I'm not altering any interface elements from the main thread in my code.
override func viewDidLoad() {
let locationManager = CLLocationManager()
locationManager.requestAlwaysAuthorization()
locationManager.requestWhenInUseAuthorization()
if CLLocationManager.locationServicesEnabled() {
locationManager.desiredAccuracy = kCLLocationAccuracyNearestTenMeters
locationManager.startUpdatingLocation()
}
viewMap.delegate = self
let camera = GMSCameraPosition.camera(withLatitude: 53.7931183329367, longitude: -1.53649874031544, zoom: 17.0)
viewMap.animate(to: camera)
}
func locationManager(manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
let locValue:CLLocationCoordinate2D = manager.location!.coordinate
print("locations = \(locValue.latitude) \(locValue.longitude)")
}
func mapView(_ mapView: GMSMapView, willMove gesture: Bool) {
}
func mapView(_ mapView: GMSMapView, idleAt position: GMSCameraPosition) {
if(moving > 1){
moving = 1
UIView.animate(withDuration: 0.5, delay: 0, animations: {
self.topBarConstraint.constant = self.topBarConstraint.constant + (self.topBar.bounds.height / 2)
self.bottomHalfConstraint.constant = self.bottomHalfConstraint.constant + (self.topBar.bounds.height / 2)
self.view.layoutIfNeeded()
}, completion: nil)
}
moving = 1
}
// Camera change Position this methods will call every time
func mapView(_ mapView: GMSMapView, didChange position: GMSCameraPosition) {
moving = moving + 1
if(moving == 2){
UIView.animate(withDuration: 0.5, delay: 0, animations: {
self.topBarConstraint.constant = self.topBarConstraint.constant - (self.topBar.bounds.height / 2)
self.bottomHalfConstraint.constant = self.bottomHalfConstraint.constant - (self.topBar.bounds.height / 2)
self.view.layoutIfNeeded()
}, completion: nil)
}
DispatchQueue.main.async {
print("Moving: \(moving) Latitude: \(self.viewMap.camera.target.latitude)")
print("Moving: \(moving) Longitude: \(self.viewMap.camera.target.longitude)")
}
}
Swift Solutions
Solution 1 - Swift
It's hard to find the UI code which is not executed in main thread sometimes. You can use the trick below to locate it and fix it.
- Choose Edit Scheme -> Diagnostics, tick Main Thread Checker.
Xcode 11.4.1
Click the small arrow next to the Main Thread Checker to create a Main Thread Checker breakpoint.
Previous Xcode
Tick on Pause on issues.
-
Run your iOS application to reproduce this issue. (Xcode should pause on the first issue.)
-
Wrap the code that modify the UI in
DispatchQueue.main.async {}
Solution 2 - Swift
First, make sure your invocations of google maps and ui changes are called from the main thread.
You can enable Thread Sanitizer option in Xcode using below steps:
You can put offending lines on the main thread with the following:
DispatchQueue.main.async {
//Do UI Code here.
//Call Google maps methods.
}
Also, update your current version of google maps. Google maps had to make a couple of updates for the thread checker.
For the question: "Why would this be occurring?" I think Apple added an assertion for an edge case which Google then had to update their pod for.
Solution 3 - Swift
Wrap the lines of code that modify the UI in DispatchQueue.main.async {} in order to make sure they execute on the main thread. Otherwise, you may be calling them from a background thread, where UI modifications are not allowed. All such lines of code must be executed from the main thread.
Solution 4 - Swift
Refer this link https://developer.apple.com/documentation/code_diagnostics/main_thread_checker
For me this worked when I called from block.
Solution 5 - Swift
I think the solution is already given, For my issue is Keyboard on the way.
Solution 6 - Swift
Choose scheme -> Diagnotics, remove main thread checker, then the warning will disappear. scheme editor