Some defense against ProfileViewController.authContext.getter Forced …

…Unwrapping Crash

Make the viewModel of the ProfileViewController optional rather than force unwrapping it. If the necessary information is not available, Profile page should show blank rather than crashing, and hopefully will have the expected info soon or the next time it is opened.

There is still a crash danger inherent in the use of TabBarPager, which requires a non-optional for several protocol methods were we can’t guarantee to have one to return. This dependency should be removed in the future.

Mastodon/Protocol/PagerTabStripNavigateable.swift

@@ -12,7 +12,7 @@ import MastodonLocalization
 typealias PagerTabStripNavigateable = PagerTabStripNavigateableCore & PagerTabStripNavigateableRelay
 
 protocol PagerTabStripNavigateableCore: AnyObject {
-    var navigateablePageViewController: PagerTabStripViewController { get }
+    var navigateablePageViewController: PagerTabStripViewController? { get }
     var pagerTabStripNavigateKeyCommands: [UIKeyCommand] { get }
 
     func pagerTabStripNavigateKeyCommandHandler(_ sender: UIKeyCommand)
@@ -82,6 +82,7 @@ extension PagerTabStripNavigateableCore where Self: PagerTabStripNavigateableRel
 
 extension PagerTabStripNavigateableCore {
     func navigate(direction: PagerTabStripNavigationDirection) {
+        guard let navigateablePageViewController = navigateablePageViewController else { return }
         let index = navigateablePageViewController.currentIndex
         let targetIndex: Int
 

Mastodon/Scene/Profile/Paging/ProfilePagingViewController.swift

@@ -23,15 +23,15 @@ final class ProfilePagingViewController: ButtonBarPagerTabStripViewController, T
     weak var pagingDelegate: ProfilePagingViewControllerDelegate?
 
     var disposeBag = Set<AnyCancellable>()
-    var viewModel: ProfilePagingViewModel!
+    var viewModel: ProfilePagingViewModel?
 
     let buttonBarShadowView = UIView()
     private var buttonBarShadowAlpha: CGFloat = 0.0
 
     // MARK: - TabBarPageViewController
 
     var currentPage: TabBarPage? {
-        return viewModel.viewControllers[currentIndex]
+        return viewModel?.viewControllers[currentIndex]
     }
 
     var currentPageIndex: Int? {
@@ -41,13 +41,13 @@ final class ProfilePagingViewController: ButtonBarPagerTabStripViewController, T
     // MARK: - ButtonBarPagerTabStripViewController
 
     override func viewControllers(for pagerTabStripController: PagerTabStripViewController) -> [UIViewController] {
-        return viewModel.viewControllers
+        return viewModel?.viewControllers ?? []
     }
 
     override func updateIndicator(for viewController: PagerTabStripViewController, fromIndex: Int, toIndex: Int, withProgressPercentage progressPercentage: CGFloat, indexWasChanged: Bool) {
         super.updateIndicator(for: viewController, fromIndex: fromIndex, toIndex: toIndex, withProgressPercentage: progressPercentage, indexWasChanged: indexWasChanged)
 
-        guard indexWasChanged else { return }
+        guard indexWasChanged, let viewModel = viewModel else { return }
         let page = viewModel.viewControllers[toIndex]
         tabBarPageViewDelegate?.pageViewController(self, didPresentingTabBarPage: page, at: toIndex)
     }
@@ -88,7 +88,7 @@ extension ProfilePagingViewController {
             buttonBarView.backgroundColor = .systemBackground
             buttonBarShadowView.pinTo(to: buttonBarView)
 
-            viewModel.$needsSetupBottomShadow
+            viewModel?.$needsSetupBottomShadow
                 .receive(on: DispatchQueue.main)
                 .sink { [weak self] needsSetupBottomShadow in
                     guard let self = self else { return }
@@ -145,7 +145,7 @@ extension ProfilePagingViewController {
     }
 
     func setupBottomShadow() {
-        guard viewModel.needsSetupBottomShadow else {
+        guard let viewModel = viewModel, viewModel.needsSetupBottomShadow else {
             buttonBarShadowView.layer.shadowColor = nil
             buttonBarShadowView.layer.shadowRadius = 0
             return
@@ -176,6 +176,7 @@ extension ProfilePagingViewController {
 extension ProfilePagingViewController {
 
     var currentViewController: (UIViewController & TabBarPage)? {
+        guard let viewModel = viewModel else { return nil }
         guard !viewModel.viewControllers.isEmpty,
               currentIndex < viewModel.viewControllers.count
         else { return nil }