Fix crash when tapping My Profile tab too quickly after app launch

Tusker/Screens/Profile/ProfileViewController.swift

@@ -14,11 +14,17 @@ class ProfileViewController: UIPageViewController {
     
     weak var mastodonController: MastodonController!
     
-    // todo: does this still need to be settable?
+    // This property is optional because MyProfileViewController may not have the user's account ID
-    var accountID: String! {
+    // when first constructed. It should never be set to nil.
+    var accountID: String? {
+        willSet {
+            if newValue == nil {
+                fatalError("Do not set ProfileViewController.accountID to nil")
+            }
+        }
         didSet {
-            updateAccountUI()
             pageControllers.forEach { $0.accountID = accountID }
+            loadAccount()
         }
     }
     
@@ -50,7 +56,9 @@ class ProfileViewController: UIPageViewController {
     }
     
     deinit {
-        mastodonController.persistentContainer.account(for: accountID)?.decrementReferenceCount()
+        if let accountID = accountID {
+            mastodonController.persistentContainer.account(for: accountID)?.decrementReferenceCount()
+        }
     }
 
     override func viewDidLoad() {
@@ -84,8 +92,12 @@ class ProfileViewController: UIPageViewController {
             .receive(on: DispatchQueue.main)
             .sink { [weak self] (_) in self?.updateAccountUI() }
         
+        loadAccount()
+    }
+    
+    private func loadAccount() {
+        guard let accountID = accountID else { return }
         if mastodonController.persistentContainer.account(for: accountID) != nil {
-            headerView.updateUI(for: accountID)
             updateAccountUI()
         } else {
             let req = Client.getAccount(id: accountID)
@@ -95,10 +107,6 @@ class ProfileViewController: UIPageViewController {
                 self.mastodonController.persistentContainer.addOrUpdate(account: account, incrementReferenceCount: true) { (account) in
                     DispatchQueue.main.async {
                         self.updateAccountUI()
-                        self.headerView.updateUI(for: self.accountID)
-                        self.pageControllers.forEach {
-                            $0.updateUI(account: account)
-                        }
                     }
                 }
             }
@@ -106,8 +114,17 @@ class ProfileViewController: UIPageViewController {
     }
     
     private func updateAccountUI() {
-        guard let account = mastodonController.persistentContainer.account(for: accountID) else { return }
+        guard let accountID = accountID,
+              let account = mastodonController.persistentContainer.account(for: accountID) else {
+            return
+        }
+        
+        // Optionally invoke updateUI on headerView because viewDidLoad may not have been called yet
+        headerView?.updateUI(for: accountID)
         navigationItem.title = account.displayNameWithoutCustomEmoji
+        pageControllers.forEach {
+            $0.updateUI(account: account)
+        }
     }
     
     private func selectPage(at index: Int, animated: Bool, completion: ((Bool) -> Void)? = nil) {
@@ -177,13 +194,15 @@ class ProfileViewController: UIPageViewController {
     // MARK: Interaction
     
     @objc private func composeMentioning() {
-        if let account = mastodonController.persistentContainer.account(for: accountID) {
+        if let accountID = accountID,
+           let account = mastodonController.persistentContainer.account(for: accountID) {
             compose(mentioningAcct: account.acct)
         }
     }
     
     private func composeDirectMentioning() {
-        if let account = mastodonController.persistentContainer.account(for: accountID) {
+        if let accountID = accountID,
+           let account = mastodonController.persistentContainer.account(for: accountID) {
             let draft = mastodonController.createDraft(mentioningAcct: account.acct)
             draft.visibility = .direct
             compose(editing: draft)