CGDisplayIOServicePort is deprecated in OS X >= 10.9, how to replace?

Question

I did small app to allow quickly change screen resolutions on multiple monitors. I want to show product name as title of the monitor, and it's very simple to find using this code:

NSDictionary *deviceInfo = (__bridge NSDictionary *)IODisplayCreateInfoDictionary(CGDisplayIOServicePort(dispID), kIODisplayOnlyPreferredName);

NSDictionary *localizedNames = [deviceInfo objectForKey:[NSString stringWithUTF8String:kDisplayProductName]];

if([localizedNames count] > 0) {
    _title = [localizedNames objectForKey:[[localizedNames allKeys] objectAtIndex:0]];
} else {
    _title = @"Unknown display";
}

But CGDisplayIOServicePort is deprecated in OS X >= 10.9 and Apple's documentation says there is no replacement. How to find service port or product name without using this method?

I tried to iterate through IO-registry and tried to use IOServiceGetMatchingServices method to find display services but I'm not very familiar with IO-registry so I couldn't find solution.

Thanks for help!

Answer 1

It looks like @Eun's post missed a piece of information to close this discussion. With a little search, I found that IOServicePortFromCGDisplayID is not an API which Apple provides. Rather, it's a piece of open source code found here: https://github.com/glfw/glfw/blob/e0a6772e5e4c672179fc69a90bcda3369792ed1f/src/cocoa_monitor.m

I copied IOServicePortFromCGDisplayID and also 'getDisplayName' from it. I needed two tweaks to make it work on OS X 10.10.

1. Remove the code to handle serial number in IOServicePortFromCGDisplayID. (CFDictionaryGetValue for kDisplaySerialNumber returns NULL for me.)
2. Remove project specific error handling code in getDisplayName.

If you need more information

• Issue tracker of the problem: github.com/glfw/glfw/issues/165
• Commit for the solution: github.com/glfw/glfw/commit/e0a6772e5e4c672179fc69a90bcda3369792ed1f

I would thank Matthew Henry who submitted the code there.

Answer 2

Here is my take on the issue. I also started with the code from GLFW 3.1, file cocoa_monitor.m.
But I had to modify it in different ways than Hiroshi said, so here goes:

// Get the name of the specified display
- (NSString*) screenNameForDisplay: (NSNumber*) screen_id
{
    CGDirectDisplayID displayID = [screen_id unsignedIntValue];

    io_service_t serv = [self IOServicePortFromCGDisplayID: displayID];
    if (serv == 0)
        return @"unknown";

    CFDictionaryRef info = IODisplayCreateInfoDictionary(serv, kIODisplayOnlyPreferredName);
    IOObjectRelease(serv);

    CFStringRef display_name;
    CFDictionaryRef names = CFDictionaryGetValue(info, CFSTR(kDisplayProductName));

    if ( !names ||
         !CFDictionaryGetValueIfPresent(names, CFSTR("en_US"), (const void**) & display_name)  )
    {
        // This may happen if a desktop Mac is running headless
        CFRelease( info );
        return @"unknown";
    }

    NSString * displayname = [NSString stringWithString: (__bridge NSString *) display_name];
    CFRelease(info);
    return displayname;
}


// Returns the io_service_t (an int) corresponding to a CG display ID, or 0 on failure.
// The io_service_t should be released with IOObjectRelease when not needed.

- (io_service_t) IOServicePortFromCGDisplayID: (CGDirectDisplayID) displayID
{
    io_iterator_t iter;
    io_service_t serv, servicePort = 0;

    CFMutableDictionaryRef matching = IOServiceMatching("IODisplayConnect");

    // releases matching for us
    kern_return_t err = IOServiceGetMatchingServices( kIOMasterPortDefault, matching, & iter );
    if ( err )
        return 0;

    while ( (serv = IOIteratorNext(iter)) != 0 )
    {
        CFDictionaryRef displayInfo;
        CFNumberRef vendorIDRef;
        CFNumberRef productIDRef;
        CFNumberRef serialNumberRef;

        displayInfo = IODisplayCreateInfoDictionary( serv, kIODisplayOnlyPreferredName );

        Boolean success;
        success =  CFDictionaryGetValueIfPresent( displayInfo, CFSTR(kDisplayVendorID),  (const void**) & vendorIDRef );
        success &= CFDictionaryGetValueIfPresent( displayInfo, CFSTR(kDisplayProductID), (const void**) & productIDRef );

        if ( !success )
        {
            CFRelease(displayInfo);
            continue;
        }

        SInt32 vendorID;
        CFNumberGetValue( vendorIDRef, kCFNumberSInt32Type, &vendorID );
        SInt32 productID;
        CFNumberGetValue( productIDRef, kCFNumberSInt32Type, &productID );

        // If a serial number is found, use it.
        // Otherwise serial number will be nil (= 0) which will match with the output of 'CGDisplaySerialNumber'
        SInt32 serialNumber = 0;
        if ( CFDictionaryGetValueIfPresent(displayInfo, CFSTR(kDisplaySerialNumber), (const void**) & serialNumberRef) )
        {
            CFNumberGetValue( serialNumberRef, kCFNumberSInt32Type, &serialNumber );
        }

        // If the vendor and product id along with the serial don't match
        // then we are not looking at the correct monitor.
        // NOTE: The serial number is important in cases where two monitors
        //       are the exact same.
        if( CGDisplayVendorNumber(displayID) != vendorID ||
            CGDisplayModelNumber(displayID)  != productID ||
            CGDisplaySerialNumber(displayID) != serialNumber )
        {
            CFRelease(displayInfo);
            continue;
        }

        servicePort = serv;
        CFRelease(displayInfo);
        break;
    }

    IOObjectRelease(iter);
    return servicePort;
}

This works fine for me in a screensaver I wrote under macOS 10.11 (El Capitan). I tested it with the built-in display of my MacBookPro and an Apple Display connected via Thunderbolt.

Answer 3

As of macOS 10.15 -[NSScreen localizedName] is available:

NSLog(@"Name of main display is %@", NSScreen.mainScreen.localizedName);

Answer 4

NSString* screenNameForDisplay(CGDirectDisplayID displayID)
{
    NSString *screenName = nil;
    io_service_t service = IOServicePortFromCGDisplayID(displayID);
    if (service)
    {
        NSDictionary *deviceInfo = (NSDictionary *)IODisplayCreateInfoDictionary(service, kIODisplayOnlyPreferredName);
        NSDictionary *localizedNames = [deviceInfo objectForKey:[NSString stringWithUTF8String:kDisplayProductName]];

        if ([localizedNames count] > 0) {
            screenName = [[localizedNames objectForKey:[[localizedNames allKeys] objectAtIndex:0]] retain];
        }

        [deviceInfo release];
    }
    return [screenName autorelease];
}