mac screensaver start event

This isn't exactly an answer to the question, but I spent a lot of time looking in vain for a list of the notifications posted by macOS, so I wanted to post some code I wrote for notification discovery.

The code simply signs up to listen to all notifications, and prints some info for each as it comes in.

import Foundation

let distCenter = CFNotificationCenterGetDistributedCenter()
if distCenter == nil {
    exit(1)
}

CFNotificationCenterAddObserver(distCenter, nil, { (center, observer, name, object, userInfo) -> Void in
        print("Event occurred: \(name)  User info: \(userInfo)")
    }, nil, nil, .DeliverImmediately)

CFRunLoopRun()

While there is no Carbon event for this, you can get notified when the current application changes, and then check to see if the new application is the screen saver process.

---

// Register the event handler for when applications change
{
    EventTypeSpec es;
    es.eventClass = kEventClassApplication;
    es.eventKind = kEventAppFrontSwitched;
    InstallApplicationEventHandler(&appChanged, 1, &es, NULL, NULL);
}

OSStatus appChanged(EventHandlerCallRef nextHandler, EventRef anEvent, void* userData)
{
    ProcessSerialNumber psn;    
    GetEventParameter(anEvent, kEventParamProcessID, typeProcessSerialNumber,
                      NULL, sizeof(psn), NULL, &psn);

    // Determine process name
    char procName[255];
    {
        ProcessInfoRec pInfo;
        Str255 procName255;
        FSRef ref;

        pInfo.processInfoLength = sizeof(ProcessInfoRec);
        pInfo.processName = procName255;
        pInfo.processAppRef = &ref;
        GetProcessInformation(&psn, &pInfo);

        const unsigned int size = (unsigned int)procName255[0];
        memcpy(procName, procName255 + 1, size);
        procName[size] = '\0';
    }

    if(strcmp(procName, "ScreenSaverEngine") == 0)
    {
        NSLog(@"Found %s\n", procName);
    }

    return noErr;
}

Finally found it — the solution is to use NSDistributedNotificationCenter and observe folowing events

• com.apple.screensaver.didstart
• com.apple.screensaver.willstop
• com.apple.screensaver.didstop
• com.apple.screenIsLocked
• com.apple.screenIsUnlocked

Like

[[NSDistributedNotificationCenter defaultCenter]
   addObserver:self
   selector:@selector(screensaverStarted:)
   name:@"com.apple.screensaver.didstart"
   object:nil];