title: NSNotification getting called multiple times
body: <p>I have the following code in my didFinishLaunchingWithOptions</p>
  
  <pre><code>  NotificationCenter.default.addObserver(
              self,
              selector: #selector(addressBookDidChange),
              name: NSNotification.Name.CNContactStoreDidChange,
              object: nil)
  </code></pre>
  
  <p>This is the method it calls </p>
  
  <pre><code>@objc func addressBookDidChange(notification: NSNotification){
                  self.processContacts()
  
      }
  </code></pre>
  
  <p>and here is the notification being removed </p>
  
  <pre><code>func applicationWillTerminate(_ application: UIApplication) {
  NotificationCenter.default.removeObserver(NSNotification.Name.CNContactStoreDidChange)
      }
  </code></pre>
  
  <p>The problem is that when I add a new contact via the method below, addressBookDidChange gets called multiple times after, not just once</p>
  
  <pre><code>func addContact(contact:ContactObject) {
          let store = CNContactStore()
  
          let contactToAdd = CNMutableContact()
          contactToAdd.givenName = contact.firstName
          contactToAdd.familyName = contact.lastName
          contactToAdd.organizationName = contact.company
  
          for case let contactNumber as PhoneNumberObject in contact.phoneNumbers!{
              let mobileNumber = CNPhoneNumber(stringValue: contactNumber.number)
              contactToAdd.phoneNumbers.append(CNLabeledValue(label: contactNumber.type.getCNLabelValue(), value: mobileNumber))
          }
  
  
          if let image = contact.image {
              contactToAdd.imageData = UIImagePNGRepresentation(image)
          }
  
          let saveRequest = CNSaveRequest()
          saveRequest.add(contactToAdd, toContainerWithIdentifier: nil)
  
          do {
              try store.execute(saveRequest)
          } catch {
              NSLog("Error adding contact \(contact.firstName) \(contact.lastName) : \(error)")
          }
      }
  </code></pre>
  
  <p>How can I make the notification be just called once for an addition of one contact?</p>