Question

I’m trying to implement a custom URL scheme for my application. I’ve added the necessary lines for my Info.plist. After calling the specified url (eg.: myapp://) the application launches.

If I want to handle the URL, I’ve found these steps:

@interface EventHandler : NSObject {
}
@end

@implementation EventHandler
- (id)init {
    self = [super init];

    if (self) {
        NSLog(@"eventHandler::init");

        NSNotificationCenter* defaultCenter = [NSNotificationCenter defaultCenter];
        [defaultCenter addObserver:self
                        selector:@selector(applicationDidFinishLaunching:)
//                        name:NSApplicationWillFinishLaunchingNotification
          name:NSApplicationDidFinishLaunchingNotification
                        object:nil];
    }
    return self;
}

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
    NSAppleEventManager *appleEventManager = [NSAppleEventManager sharedAppleEventManager];
    [appleEventManager setEventHandler:self andSelector:@selector(handleGetURLEvent:withReplyEvent:) forEventClass:kInternetEventClass andEventID:kAEGetURL];
}

- (void)handleGetURLEvent:(NSAppleEventDescriptor *)event withReplyEvent:(NSAppleEventDescriptor *)replyEvent
{
    NSString* url = [[event paramDescriptorForKeyword:keyDirectObject] stringValue];
    NSLog(@"%@", url);
}

@end

The above code is working if the application is running, but if the URL gets called and the application was terminated, the event is not caught. I think this is because this: NSApplicationDidFinishLaunchingNotification.
Changing it to NSApplicationWillFinishLaunchingNotification causes that non events caught. Maybe Qt handles it before me, but I can’t find a workaround for the problem.

Answer 1

I was also trying to get my Qt-based application handle a custom URL scheme on the Mac and went down the same path as the original poster. It turns out that Qt4 already supports URL events on the Mac, and there’s no need to write Objective-C code to receive them. This is in fact the reason that you didn’t receive any URL events when you set the event handler in response to NSApplicationWillFinishLaunchingNotification: Qt registers its own handler afterward.

When a URL with your custom scheme is triggered, your Qt application will receive a FileOpenEvent. Note that it is the QApplication instance which receives the event. You can catch it by making your application subclass QApplication or by installing an event filter on the standard QApplication. I opted for this second approach.

Here’s the eventFilter method of my custom event filter class, FileOpenEventFilter. It just emits the signal urlOpened when the event contains a non-empty URL. It also saves the last opened URL in case my main window isn’t completely initialized when the event arrives (which happens in my app when it’s not already running when the custom URL is clicked.)

bool FileOpenEventFilter::eventFilter(QObject* obj, QEvent* event)
{
    if (event->type() == QEvent::FileOpen)
    {
        QFileOpenEvent* fileEvent = static_cast<QFileOpenEvent*>(event);
        if (!fileEvent->url().isEmpty())
        {
            m_lastUrl = fileEvent->url().toString();
            emit urlOpened(m_lastUrl);
        }
        else if (!fileEvent->file().isEmpty())
        {
            emit fileOpened(fileEvent->file());
        }

        return false;
    }
    else
    {
        // standard event processing
        return QObject::eventFilter(obj, event);
    }
}