fix: ios view registration race condition (#555)

Co-authored-by: Joonas Kerttula <[email protected]>

Author: illuminati1911

ios/google_navigation_flutter/Sources/google_navigation_flutter/GoogleMapsNavigationView.swift

@@ -133,7 +133,8 @@ public class GoogleMapsNavigationView: NSObject, FlutterPlatformView, ViewSettle
       _viewRegistry.unregisterCarPlayView()
     } else {
       if let _viewId {
-        _viewRegistry.unregisterView(viewId: _viewId)
+        let viewInstanceId = ObjectIdentifier(self)
+        _viewRegistry.unregisterView(viewId: _viewId, viewInstanceIdToUnregister: viewInstanceId)
       }
     }
   }

ios/google_navigation_flutter/Sources/google_navigation_flutter/GoogleMapsNavigationViewRegistry.swift

@@ -33,16 +33,16 @@ class GoogleMapsNavigationViewRegistry {
   )
 
   func registerView(viewId: Int64, view: GoogleMapsNavigationView) {
-    queue.async(flags: .barrier) { [weak self] in
-      DispatchQueue.main.async {
-        self?.views[viewId] = view
-      }
+    queue.sync(flags: .barrier) { [weak self] in
+      self?.views[viewId] = view
     }
   }
 
-  func unregisterView(viewId: Int64) {
+  func unregisterView(viewId: Int64, viewInstanceIdToUnregister: ObjectIdentifier) {
     queue.async(flags: .barrier) { [weak self] in
-      DispatchQueue.main.async {
+      if let registeredView = self?.views[viewId],
+        ObjectIdentifier(registeredView) == viewInstanceIdToUnregister
+      {
         self?.views.removeValue(forKey: viewId)
       }
     }