avoid calling [UIApplication sharedApplication] in app extensions

Firebase/Messaging/FIRMessaging.m

@@ -378,7 +378,10 @@ - (void)handleIncomingLinkIfNeededFromMessage:(NSDictionary *)message {
     });
     return;
   }
-  UIApplication *application = [UIApplication sharedApplication];
+  UIApplication *application = FIRMessagingUIApplication();
+  if (!application) {
+    return;
+  }
   id<UIApplicationDelegate> appDelegate = application.delegate;
   SEL continueUserActivitySelector =
       @selector(application:continueUserActivity:restorationHandler:);
@@ -611,7 +614,11 @@ - (BOOL)shouldBeConnectedAutomatically {
   // We require a token from Instance ID
   NSString *token = self.defaultFcmToken;
   // Only on foreground connections
-  UIApplicationState applicationState = [UIApplication sharedApplication].applicationState;
+  UIApplication *application = FIRMessagingUIApplication();
+  if (!application) {
+    return NO;
+  }
+  UIApplicationState applicationState = application.applicationState;
   BOOL shouldBeConnected = _shouldEstablishDirectChannel &&
                            (token.length > 0) &&
                            applicationState == UIApplicationStateActive;

Firebase/Messaging/FIRMessagingContextManagerService.m

@@ -20,6 +20,7 @@
 
 #import "FIRMessagingDefines.h"
 #import "FIRMessagingLogger.h"
+#import "FIRMessagingUtilities.h"
 
 #define kFIRMessagingContextManagerPrefixKey @"google.c.cm."
 #define kFIRMessagingContextManagerNotificationKeyPrefix @"gcm.notification."
@@ -174,7 +175,11 @@ + (void)scheduleLocalNotificationForMessage:(NSDictionary *)message
   }
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wdeprecated-declarations"
-  [[UIApplication sharedApplication] scheduleLocalNotification:notification];
+  UIApplication *application = FIRMessagingUIApplication();
+  if (!application) {
+    return;
+  }
+  [application scheduleLocalNotification:notification];
 #pragma clang diagnostic pop
 }
 

Firebase/Messaging/FIRMessagingReceiver.m

@@ -19,8 +19,9 @@
 #import <UIKit/UIKit.h>
 
 #import "FIRMessaging.h"
-#import "FIRMessaging_Private.h"
 #import "FIRMessagingLogger.h"
+#import "FIRMessagingUtilities.h"
+#import "FIRMessaging_Private.h"
 
 static NSString *const kUpstreamMessageIDUserInfoKey = @"messageID";
 static NSString *const kUpstreamErrorUserInfoKey = @"error";
@@ -111,19 +112,23 @@ - (void)scheduleNotificationForMessage:(NSDictionary *)message {
   SEL oldNotificationSelector = @selector(application:didReceiveRemoteNotification:);
 
   dispatch_async(dispatch_get_main_queue(), ^{
-    id<UIApplicationDelegate> appDelegate = [[UIApplication sharedApplication] delegate];
+    UIApplication *application = FIRMessagingUIApplication();
+    if (!application) {
+      return;
+    }
+    id<UIApplicationDelegate> appDelegate = [application delegate];
     if ([appDelegate respondsToSelector:newNotificationSelector]) {
       // Try the new remote notification callback
-      [appDelegate application:[UIApplication sharedApplication]
-  didReceiveRemoteNotification:message
-        fetchCompletionHandler:^(UIBackgroundFetchResult result) {}];
+      [appDelegate application:application
+          didReceiveRemoteNotification:message
+                fetchCompletionHandler:^(UIBackgroundFetchResult result) {
+                }];
 
     } else if ([appDelegate respondsToSelector:oldNotificationSelector]) {
       // Try the old remote notification callback
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wdeprecated-declarations"
-      [appDelegate application:
-       [UIApplication sharedApplication] didReceiveRemoteNotification:message];
+      [appDelegate application:application didReceiveRemoteNotification:message];
 #pragma clang diagnostic pop
     } else {
       FIRMessagingLoggerError(kFIRMessagingMessageCodeReceiver005,

Firebase/Messaging/FIRMessagingRemoteNotificationsProxy.m

@@ -21,6 +21,7 @@
 
 #import "FIRMessagingConstants.h"
 #import "FIRMessagingLogger.h"
+#import "FIRMessagingUtilities.h"
 #import "FIRMessaging_Private.h"
 
 static const BOOL kDefaultAutoRegisterEnabledValue = YES;
@@ -98,7 +99,11 @@ - (void)swizzleMethodsIfPossible {
     return;
   }
 
-  NSObject<UIApplicationDelegate> *appDelegate = [[UIApplication sharedApplication] delegate];
+  UIApplication *application = FIRMessagingUIApplication();
+  if (!application) {
+    return;
+  }
+  NSObject<UIApplicationDelegate> *appDelegate = [application delegate];
   [self swizzleAppDelegateMethods:appDelegate];
 
   // Add KVO listener on [UNUserNotificationCenter currentNotificationCenter]'s delegate property

Firebase/Messaging/FIRMessagingUtilities.h

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-#import <Foundation/Foundation.h>
+#import <UIKit/UIKit.h>
 
 typedef NS_ENUM(int8_t, FIRMessagingProtoTag) {
   kFIRMessagingProtoTagInvalid = -1,
@@ -51,4 +51,8 @@ FOUNDATION_EXPORT int64_t FIRMessagingCurrentTimestampInMilliseconds(void);
 FOUNDATION_EXPORT NSString *FIRMessagingCurrentAppVersion(void);
 FOUNDATION_EXPORT NSString *FIRMessagingAppIdentifier(void);
 
+#pragma mark - Others
+
 FOUNDATION_EXPORT uint64_t FIRMessagingGetFreeDiskSpaceInMB(void);
+FOUNDATION_EXPORT UIApplication *FIRMessagingUIApplication(void);
+

Firebase/Messaging/FIRMessagingUtilities.m

@@ -20,6 +20,8 @@
 
 #import "FIRMessagingLogger.h"
 
+#import <GoogleUtilities/GULAppEnvironmentUtil.h>
+
 // Convert the macro to a string
 #define STR_EXPAND(x) #x
 #define STR(x) STR_EXPAND(x)
@@ -171,3 +173,16 @@ uint64_t FIRMessagingGetFreeDiskSpaceInMB(void) {
     return 0;
   }
 }
+
+UIApplication *FIRMessagingUIApplication(void) {
+  static Class applicationClass = nil;
+  // iOS App extensions should not call [UIApplication sharedApplication], even if UIApplication
+  // responds to it.
+  if (![GULAppEnvironmentUtil isAppExtension]) {
+    Class cls = NSClassFromString(@"UIApplication");
+    if (cls && [cls respondsToSelector:NSSelectorFromString(@"sharedApplication")]) {
+      applicationClass = cls;
+    }
+  }
+  return [applicationClass sharedApplication];
+}