I called the viewWillDisappear method in UIViewController AVCaptureSession *session = self.session; dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ if (!session.running) { [session startRunning]; } }); I called the viewWillDisappear method dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ AVCaptureSession *session = self.session; if (session && session.running) { [session stopRunning]; } }); But when the user exits the background and returns to the current page, clicking 'Return' will cause an exception Abnormal information: #36 Thread SIGSEGV SEGV_ACCERR libdispatch.dylib _dispatch_source_set_timer + 32 one PrivacyAccounting 0x00000001a5ede000 + 533590244180685288 two PrivacyAccounting 0x00000001a5ede000 + 533590244180685288 three PrivacyAccounting 0x00000001a5ede000 + 1236823037899193652 four libdispatch.dylib 0x000000018ea01000 + 3414669699500290324 libsystem_pthread.dylib _pthread_wqthread + 14360117738498687264