CODEWITHSUNDEEP
c++objective-cqtnsnotificationcentercore-foundation
Vishakha
Vishakha

Reputation: 36

How to fix the crash in CFNotificationCenterAddObserver for NSWorkspaceDidActivateApplicationNotification?

Not very much accustom to Objective C, hence trying to observe NSWorkspaceDidActivateApplicationNotification event in C++ code with CFNotificationCenterAddObserver() method.

#include<CoreFoundation/CFNotificationCenter.h>
#include<iostream>
#include<QGuiApplication>

void Callback (CFNotificationCenterRef center, void* observer, CFNotificationName name,
               const void* object,
               CFDictionaryRef userInfo)
{
  std::cout << "Hello World\n";
  //NSLog(@"New application: %@", [[name userInfo] objectForKey:NSWorkspaceApplicationKey]);
}

int main (int argc, char** argv)
{
  QGuiApplication application(argc, argv);

  std::cout << "Add observer\n";
  CFNotificationCenterAddObserver(CFNotificationCenterGetDistributedCenter(), nullptr, Callback,
                                  CFStringRef("NSWorkspaceDidActivateApplicationNotification"), nullptr,
                                  CFNotificationSuspensionBehaviorDeliverImmediately);
  std::cout << "Added ...\n";
  return application.exec();
}

However it results in below crash. If I try to run in debug mode, then it sometimes shows the below crash or sometimes get stuck in that function itself.

Add observer
2021-12-03 21:44:24.527086+0530 Test[17288:982994] -[__NSTaggedDate length]: unrecognized selector sent to instance 0x100007c65
2021-12-03 21:44:24.527916+0530 Test[17288:982994] [General] An uncaught exception was raised
2021-12-03 21:44:24.527943+0530 Test[17288:982994] [General] -[__NSTaggedDate length]: unrecognized selector sent to instance 0x100007c65
2021-12-03 21:44:24.528044+0530 Test[17288:982994] [General] (
    0   CoreFoundation                      0x00007fff35570035 __exceptionPreprocess + 256
    1   libobjc.A.dylib                     0x00007fff5fc80a17 objc_exception_throw + 48
    2   CoreFoundation                      0x00007fff355e9fce -[NSObject(NSObject) __retain_OA] + 0
    3   CoreFoundation                      0x00007fff35511e9f ___forwarding___ + 1485
    4   CoreFoundation                      0x00007fff35511848 _CF_forwarding_prep_0 + 120
    5   CoreFoundation                      0x00007fff355aca4c __CFXNotificationRegisterObserver + 588
    6   CoreFoundation                      0x00007fff3548a037 CFNotificationCenterAddObserver + 204
    7   Test                                0x00000001000066a1 main + 129
    8   libdyld.dylib                       0x00007fff614503d5 start + 1
)
2021-12-03 21:44:24.528241+0530 Test[17288:982994] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSTaggedDate length]: unrecognized selector sent to instance 0x100007c65'
*** First throw call stack:
(
    0   CoreFoundation                      0x00007fff35570035 __exceptionPreprocess + 256
    1   libobjc.A.dylib                     0x00007fff5fc80a17 objc_exception_throw + 48
    2   CoreFoundation                      0x00007fff355e9fce -[NSObject(NSObject) __retain_OA] + 0
    3   CoreFoundation                      0x00007fff35511e9f ___forwarding___ + 1485
    4   CoreFoundation                      0x00007fff35511848 _CF_forwarding_prep_0 + 120
    5   CoreFoundation                      0x00007fff355aca4c __CFXNotificationRegisterObserver + 588
    6   CoreFoundation                      0x00007fff3548a037 CFNotificationCenterAddObserver + 204
    7   Test                                0x00000001000066a1 main + 129
    8   libdyld.dylib                       0x00007fff614503d5 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException

How to fix this?

Upvotes: 2

Views: 317

Answers (1)

battlmonstr
battlmonstr

Reputation: 6290

Use CFSTR macro to create a CFStringRef from a constant C string like so:

CFSTR("NSWorkspaceDidActivateApplicationNotification")

NSWorkspaceDidActivateApplicationNotification docs says that you have to use NSWorkspace.notificationCenter to receive it, CFNotificationCenterGetDistributedCenter won't work.

Upvotes: 1

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