duplicate app-icon badge counter to chat's tab-bar-item

both badge counters will show the same number in the same layout.
if notifications are disabled, both counters are hidden
(the badges beside chats stay)

in practise, this feels totally normal and correctly,
this behavior is known from many other apps on iOS.

this also resets the counter on app start,
maybe fixing some rare bugs where the counter is wrong on the app icon

deltachat-ios/AppDelegate.swift

@@ -284,6 +284,7 @@ class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterD
         logger.info("➡️ applicationDidBecomeActive")
         UserDefaults.setMainIoRunning()
         applicationInForeground = true
+        NotificationManager.updateBadgeCounters()
     }
 
     func applicationWillResignActive(_: UIApplication) {

deltachat-ios/Controller/Settings/SettingsViewController.swift

@@ -246,7 +246,7 @@ internal final class SettingsViewController: UITableViewController {
             NotificationManager.removeAllNotifications()
         }
         UserDefaults.standard.synchronize()
-        NotificationManager.updateApplicationIconBadge(forceZero: !sender.isOn)
+        NotificationManager.updateBadgeCounters(disable: !sender.isOn)
     }
 
     // MARK: - updates

deltachat-ios/Coordinator/AppCoordinator.swift

@@ -230,7 +230,7 @@ class AppCoordinator: NSObject {
         // the applicationIconBadgeNumber is remembered by the system even on reinstalls (just tested on ios 13.3.1),
         // to avoid appearing an old number of a previous installation, we reset the counter manually.
         // but even when this changes in ios, we need the reset as we allow account-deletion also in-app.
-        NotificationManager.updateApplicationIconBadge(forceZero: true)
+        NotificationManager.updateBadgeCounters(disable: true)
     }
 
     func presentTabBarController() {
@@ -271,6 +271,7 @@ class AppCoordinator: NSObject {
                                                   createChatsNavigationController(),
                                                   createSettingsNavigationController()], animated: false)
         presentTabBarController()
+        NotificationManager.updateBadgeCounters()
     }
 }
 

deltachat-ios/Helper/NotificationManager.swift

@@ -22,9 +22,19 @@ public class NotificationManager {
         dcContext = dcAccounts.getSelected()
     }
 
-    public static func updateApplicationIconBadge(forceZero: Bool = false) {
+    public static func updateBadgeCounters(disable: Bool = false) {
         DispatchQueue.main.async {
-            UIApplication.shared.applicationIconBadgeNumber = forceZero ? 0 : DcAccounts.shared.getFreshMessageCount()
+            let number = disable ? 0 : DcAccounts.shared.getFreshMessageCount()
+
+            // update badge counter on iOS homescreen
+            UIApplication.shared.applicationIconBadgeNumber = number
+
+            // update badge counter on our tabbar
+            if let appDelegate = UIApplication.shared.delegate as? AppDelegate,
+               let appCoordinator = appDelegate.appCoordinator,
+               let chatsNavigationController = appCoordinator.tabBarController.viewControllers?[appCoordinator.chatsTab] {
+                chatsNavigationController.tabBarItem.badgeValue = number > 0 ? "\(number)" : nil
+            }
         }
     }
 
@@ -55,7 +65,7 @@ public class NotificationManager {
                 nc.removeDeliveredNotifications(withIdentifiers: toRemove)
             }
 
-            NotificationManager.updateApplicationIconBadge()
+            NotificationManager.updateBadgeCounters()
         }
     }
 
@@ -65,7 +75,7 @@ public class NotificationManager {
             object: nil, queue: OperationQueue.main
         ) { _ in
             if !UserDefaults.standard.bool(forKey: "notifications_disabled") {
-                NotificationManager.updateApplicationIconBadge()
+                NotificationManager.updateBadgeCounters()
             }
         }