iOS 13: threading violation: expected the main thread

问题

The app is being crashed when trying to hide the navigation bar for a viewcontroller only for iOS 13 users.

• I got the crash on Crashlytics of Fabric which titled as below,

Fatal Exception: NSInternalInconsistencyException

threading violation: expected the main thread

• The app is being crashed on this line of viewWillAppear method,

    self.navigationController?.isNavigationBarHidden = true

• To hide the navigation bar on the viewWillAppear method of UIViewController, I am using below code,

    override func viewWillAppear(_ animated: Bool) {
        self.navigationController?.isNavigationBarHidden = true
        super.viewWillAppear(animated)
    }

• To show the navigation bar on the viewWillDisappear method of UIViewController, I am using below code,

    override func viewWillDisappear(_ animated: Bool) {
        self.navigationController?.isNavigationBarHidden = false
        super.viewWillDisappear(animated)
    }

回答1:

do following action

  DispatchQueue.main.async {
    self.navigationController?.isNavigationBarHidden = false
  }

来源：https://stackoverflow.com/questions/58335061/ios-13-threading-violation-expected-the-main-thread