Question

If I call CFUserNotificationDisplayAlert() to display an alert box, it prints the following message in the console:

CFUserNotificationDisplayAlert:  called from main application thread, will block waiting for a response.

I don’t want this message printed. Is there any way to disable it? Or, is there a better way to go about this? Thanks!

Answer 1

CFUserNotificationDisplayAlert() is a convenience function that always blocks the main thread while waiting for user input. If you don’t want to block the main thread, you’ll have to create the CFUserNotification yourself and attach it to the main thread’s runloop:

// First, add member variables in your class to store the user notification and runloop source, like this.  You'll need to be able to access these variables later, from your callback method:
CFUserNotificationRef _userNotification;
CFRunLoopSourceRef _runLoopSource;

// When you want to show the alert, you will create it, create a runloop source for it, then attach the runloop source to the runloop:
_userNotification= CFUserNotificationCreate(... set this up the way you want to ...);
_runLoopSource = CFUserNotificationCreateRunLoopSource(NULL, userNotification, YourUserNotificationCallback, 0);
CFRunLoopAddSource(CFRunLoopGetMain(), runLoopSource, kCFRunLoopCommonModes);

// ...elsewhere, you'll need to define your callback function, something like this:
void YourUserNotificationCallback(CFUserNotificationRef userNotification, CFOptionFlags responseFlags)
{
    // Handle the user's input here.
    ...

    // Release your notification and runloop source:
    CFRunLoopRemoveSource(CFRunLoopGetMain(), _runLoopSource, kCFRunLoopCommonModes);
    CFRelease(_runLoopSource);
    CFRelease(_userNotification);
}