Determine when NSSlider knob is 'let go' in continuous mode

Took me a little while to find this thread, but the accepted answer (although old) is great for detecting NSSlider state changes (slider value stopped changing being the main one I was looking for)!

Answer in Swift (Swift 4.1):

let slider = NSSlider(value: 1,
                      minValue: 0,
                      maxValue: 4,
                      target: self,
                      action: #selector(sliderValueChanged(sender:)))

. . .

@objc func sliderValueChanged(sender: Any) {

    guard let slider = sender as? NSSlider, 
          let event = NSApplication.shared.currentEvent else { return }

    switch event.type {
    case .leftMouseDown, .rightMouseDown:
        print("slider value started changing")
    case .leftMouseUp, .rightMouseUp:
        print("slider value stopped changing: \(slider.doubleValue)")
    case .leftMouseDragged, .rightMouseDragged:
        print("slider value changed: \(slider.doubleValue)")
    default:
        break
    }
}

Note: the right event types account for someone who has reversed their mouse buttons 🤔.

You could also simply check the type of the current event in the action method:

- (IBAction)sliderChanged:(id)sender
{
    NSEvent *currentEvent = [[sender window] currentEvent];
    if ([currentEvent type] == NSLeftMouseUp) {
        // the slider was let go
    }
}

This works for me (and is easier than subclassing NSSlider):

- (IBAction)sizeSliderValueChanged:(id)sender {
    NSEvent *event = [[NSApplication sharedApplication] currentEvent];
    BOOL startingDrag = event.type == NSLeftMouseDown;
    BOOL endingDrag = event.type == NSLeftMouseUp;
    BOOL dragging = event.type == NSLeftMouseDragged;

    NSAssert(startingDrag || endingDrag || dragging, @"unexpected event type caused slider change: %@", event);

    if (startingDrag) {
        NSLog(@"slider value started changing");
        // do whatever needs to be done when the slider starts changing
    }

    // do whatever needs to be done for "uncommitted" changes
    NSLog(@"slider value: %f", [sender doubleValue]);

    if (endingDrag) {
        NSLog(@"slider value stopped changing");
        // do whatever needs to be done when the slider stops changing
    }
}