Fix nav bars during registration & change number

The new OWSNavigationController design handles showing/hiding the nav
bar. The code in this class was fighting against it, which caused the
nav bars to appear/disappear unexpectedly throughout the process.

The vc.navigationController.navigationItem.backBarButtonItem.isEnabled
code also appears to be a no-op. A view controller should configure its
own navigationItem (ie vc.navigationItem), not that of its
navigationController. Furthermore, backBarButtonItem isn't set to what's
actually shown -- this is an opportunity to override what should be
shown to our own custom button.

Signal/src/ViewControllers/Registration/ChangePhoneNumber/ChangePhoneNumberCaptchaViewController.swift

@@ -58,12 +58,9 @@ extension ChangePhoneNumberCaptchaViewController: RegistrationCaptchaViewControl
 
         changePhoneNumberController.requestVerification(fromViewController: self, isSMS: true) { [weak self] willDismiss, _ in
 
-            if let self = self,
-               !willDismiss {
-                RegistrationBaseViewController.restoreBackButton(self)
-
-                // There's nothing left to do here. If onboardingController isn't taking us anywhere, let's
-                // just pop back to the phone number verification controller
+            if let self = self, !willDismiss {
+                // There's nothing left to do here. If onboardingController isn't taking us
+                // anywhere, let's just pop back to the phone number confirm controller
                 self.navigationController?.popViewController(animated: true)
             }
             viewModel.removeProgressView(progressView)

Signal/src/ViewControllers/Registration/ChangePhoneNumber/ChangePhoneNumberController.swift

@@ -128,8 +128,6 @@ class ChangePhoneNumberController: Dependencies {
             return
         }
 
-        RegistrationBaseViewController.restoreBackButton(changePhoneNumberViewFromViewController)
-
         if didSucceed {
             guard let newPhoneNumber = newPhoneNumber else {
                 owsFailDebug("Missing new number.")

Signal/src/ViewControllers/Registration/ChangePhoneNumber/ChangePhoneNumberVerificationViewController.swift

@@ -63,11 +63,6 @@ public class ChangePhoneNumberVerificationViewController: RegistrationBaseViewCo
 
     // MARK: - Methods
 
-    @objc
-    public func hideBackLink() {
-        backLink?.isHidden = true
-    }
-
     @objc
     public func setVerificationCodeAndTryToVerify(_ verificationCode: String) {
         AssertIsOnMainThread()
@@ -137,8 +132,6 @@ extension ChangePhoneNumberVerificationViewController: RegistrationVerificationV
 
         Logger.info("")
 
-        RegistrationBaseViewController.restoreBackButton(self)
-
         let phoneNumberVC = navigationController?.viewControllers
             .filter { $0 is ChangePhoneNumberSplashViewController }.last
 

Signal/src/ViewControllers/Registration/RegistrationBaseViewController.swift

@@ -6,7 +6,7 @@
 import UIKit
 
 @objc
-public class RegistrationBaseViewController: OWSViewController {
+public class RegistrationBaseViewController: OWSViewController, OWSNavigationChildController {
 
     // MARK: - Factory Methods
 
@@ -109,34 +109,12 @@ public class RegistrationBaseViewController: OWSViewController {
         navigationController?.popViewController(animated: true)
     }
 
-    @objc
-    public var shouldHideBackButton = true
-
-    public override func viewWillAppear(_ animated: Bool) {
-        super.viewWillAppear(animated)
-
-        if shouldHideBackButton {
-            Self.hideBackButton(self)
-        }
+    public var prefersNavigationBarHidden: Bool {
+        true
     }
 
-    public override func viewDidAppear(_ animated: Bool) {
-        super.viewDidAppear(animated)
-
-        if shouldHideBackButton {
-            Self.hideBackButton(self)
-        }
-    }
-
-    public static func hideBackButton(_ vc: UIViewController) {
-        vc.navigationController?.isNavigationBarHidden = true
-        // Disable "back" gesture.
-        vc.navigationController?.navigationItem.backBarButtonItem?.isEnabled = false
-    }
-
-    public static func restoreBackButton(_ vc: UIViewController) {
-        vc.navigationController?.isNavigationBarHidden = false
-        vc.navigationController?.navigationItem.backBarButtonItem?.isEnabled = true
+    public var shouldCancelNavigationBack: Bool {
+        true
     }
 
     // The margins for `primaryView` will update to reflect the current traitCollection.

Signal/src/ViewControllers/Registration/SecondaryLinking/ProvisioningController.swift

@@ -51,7 +51,6 @@ public class ProvisioningController: NSObject {
         navController.setViewControllers([vc], animated: false)
 
         provisioningController.awaitProvisioning(from: vc, navigationController: navController)
-        navController.isNavigationBarHidden = true
         CurrentAppContext().mainWindow?.rootViewController = navController
     }
 

Signal/src/util/RegistrationUtils.swift

@@ -46,7 +46,6 @@ public extension RegistrationUtils {
                         viewController.hideBackLink()
                         let navigationController = OnboardingNavigationController(onboardingController: onboardingController)
                         navigationController.setViewControllers([ viewController ], animated: false)
-                        navigationController.isNavigationBarHidden = true
                         let window: UIWindow = CurrentAppContext().mainWindow!
                         window.rootViewController = navigationController
                     }