fix: Reading applicationState in the background

CHANGELOG.md

@@ -10,6 +10,7 @@
 
 - Stop sending empty thread names (#3361)
 - Work around edge case with a thread info kernel call sometimes returning invalid data, leading to a crash (#3364)
+- Reading applicationState in the background (#3372)
 
 ## 8.14.2
 

Sources/Sentry/SentryUIApplication.m

@@ -4,7 +4,34 @@
 
 #    import <UIKit/UIKit.h>
 
-@implementation SentryUIApplication
+@implementation SentryUIApplication {
+    UIApplicationState appState;
+}
+
+- (instancetype)init
+{
+    if (self = [super init]) {
+        [NSNotificationCenter.defaultCenter addObserver:self
+                                               selector:@selector(didEnterBackground)
+                                                   name:UIApplicationDidEnterBackgroundNotification
+                                                 object:nil];
+
+        [NSNotificationCenter.defaultCenter addObserver:self
+                                               selector:@selector(didBecomeActive)
+                                                   name:UIApplicationDidBecomeActiveNotification
+                                                 object:nil];
+        // We store the application state when the app is initialized
+        // and we keep track of its changes by the notifications
+        // this way we avoid calling sharedApplication in a background thread
+        appState = self.sharedApplication.applicationState;
+    }
+    return self;
+}
+
+- (void)dealloc
+{
+    [NSNotificationCenter.defaultCenter removeObserver:self];
+}
 
 - (UIApplication *)sharedApplication
 {
@@ -58,7 +85,17 @@ - (UIApplication *)sharedApplication
 
 - (UIApplicationState)applicationState
 {
-    return self.sharedApplication.applicationState;
+    return appState;
+}
+
+- (void)didEnterBackground
+{
+    appState = UIApplicationStateBackground;
+}
+
+- (void)didBecomeActive
+{
+    appState = UIApplicationStateActive;
 }
 
 @end