Don't use mainApplicationState in business logic.

Signal/src/util/MainAppContext.m

@@ -120,6 +120,11 @@ NS_ASSUME_NONNULL_BEGIN
     [[UIApplication sharedApplication] setStatusBarStyle:statusBarStyle];
 }
 
+- (BOOL)isInBackground
+{
+    return [UIApplication sharedApplication].applicationState == UIApplicationStateBackground;
+}
+
 - (UIApplicationState)mainApplicationState
 {
     return [UIApplication sharedApplication].applicationState;

SignalMessaging/Views/ThreadViewHelper.m

@@ -64,8 +64,7 @@ NS_ASSUME_NONNULL_BEGIN
                                                  name:OWSApplicationDidEnterBackgroundNotification
                                                object:nil];
 
-    self.shouldObserveDBModifications
-        = !(CurrentAppContext().isMainApp && CurrentAppContext().mainApplicationState == UIApplicationStateBackground);
+    self.shouldObserveDBModifications = !CurrentAppContext().isInBackground;
 }
 
 - (void)applicationWillEnterForeground:(NSNotification *)notification

SignalMessaging/contacts/SystemContactsFetcher.swift

@@ -401,12 +401,10 @@ public class SystemContactsFetcher: NSObject {
 
         switch authorizationStatus {
         case .notDetermined:
-            if CurrentAppContext().isMainApp {
-               if CurrentAppContext().mainApplicationState() == .background {
-                    Logger.error("\(self.TAG) do not request contacts permission when app is in background")
-                    completion(nil)
-                    return
-                }
+            if CurrentAppContext().isInBackground() {
+                Logger.error("\(self.TAG) do not request contacts permission when app is in background")
+                completion(nil)
+                return
             }
             self.contactStoreAdapter.requestAccess { (granted, error) in
                 if let error = error {

SignalServiceKit/src/Storage/OWSStorage.m

@@ -531,8 +531,7 @@ static NSString *keychainDBPassAccount = @"TSDatabasePass";
         [DDLog flushLog];
 
         if (CurrentAppContext().isMainApp) {
-            UIApplicationState applicationState = CurrentAppContext().mainApplicationState;
-            if (applicationState == UIApplicationStateBackground) {
+            if (CurrentAppContext().isInBackground) {
                 // TODO: Rather than crash here, we should detect the situation earlier
                 // and exit gracefully - (in the app delegate?). See the `
                 // This is a last ditch effort to avoid blowing away the user's database.
@@ -572,8 +571,7 @@ static NSString *keychainDBPassAccount = @"TSDatabasePass";
 
 - (void)backgroundedAppDatabasePasswordInaccessibleWithErrorDescription:(NSString *)errorDescription
 {
-    OWSAssert(
-        CurrentAppContext().isMainApp && CurrentAppContext().mainApplicationState == UIApplicationStateBackground);
+    OWSAssert(CurrentAppContext().isMainApp && CurrentAppContext().isInBackground);
 
     // Sleep to give analytics events time to be delivered.
     [NSThread sleepForTimeInterval:5.0f];

SignalServiceKit/src/Util/AppContext.h

@@ -34,9 +34,13 @@ typedef void (^BackgroundTaskExpirationHandler)(void);
 
 // Should only be called if isMainApp is YES.
 //
-// In general, isMainAppAndActive will probably yield more readable code.
+// Wherever possible, use isMainAppAndActive or isInBackground instead.
+// This should only be used by debugging/logging code.
 - (UIApplicationState)mainApplicationState;
 
+// Similar to UIApplicationStateBackground, but works in SAE.
+- (BOOL)isInBackground;
+
 // Should start a background task if isMainApp is YES.
 // Should just return UIBackgroundTaskInvalid if isMainApp is NO.
 - (UIBackgroundTaskIdentifier)beginBackgroundTaskWithExpirationHandler:

SignalShareExtension/utils/ShareAppExtensionContext.m

@@ -11,6 +11,7 @@ NS_ASSUME_NONNULL_BEGIN
 @interface ShareAppExtensionContext ()
 
 @property (nonatomic) UIViewController *rootViewController;
+@property (atomic) BOOL isSAEInBackground;
 
 @end
 
@@ -63,6 +64,8 @@ NS_ASSUME_NONNULL_BEGIN
 
     DDLogInfo(@"%@ %s", self.logTag, __PRETTY_FUNCTION__);
 
+    self.isSAEInBackground = NO;
+
     [NSNotificationCenter.defaultCenter postNotificationName:OWSApplicationDidBecomeActiveNotification object:nil];
 }
 
@@ -83,6 +86,8 @@ NS_ASSUME_NONNULL_BEGIN
     DDLogInfo(@"%@ %s", self.logTag, __PRETTY_FUNCTION__);
     [DDLog flushLog];
 
+    self.isSAEInBackground = YES;
+
     [NSNotificationCenter.defaultCenter postNotificationName:OWSApplicationDidEnterBackgroundNotification object:nil];
 }
 
@@ -92,6 +97,8 @@ NS_ASSUME_NONNULL_BEGIN
 
     DDLogInfo(@"%@ %s", self.logTag, __PRETTY_FUNCTION__);
 
+    self.isSAEInBackground = NO;
+
     [NSNotificationCenter.defaultCenter postNotificationName:OWSApplicationWillEnterForegroundNotification object:nil];
 }
 
@@ -121,6 +128,11 @@ NS_ASSUME_NONNULL_BEGIN
     DDLogInfo(@"Ignoring request to set status bar style since we're in an app extension");
 }
 
+- (BOOL)isInBackground
+{
+    return self.isSAEInBackground;
+}
+
 - (UIApplicationState)mainApplicationState
 {
     OWSFail(@"%@ called %s.", self.logTag, __PRETTY_FUNCTION__);