objective c - Determine when NSSlider knob is 'let go' in continuous mode

Question

I'm using an NSSlider control, and I've configured it to use continuous mode so that I can continually update an NSTextField with the current value of the slider while the user is sliding it around. The issue I have is that I don't want to 'commit' the value until the user lets go of the knob, i.e I don't want my application to take account of the value unless the user lets go of the slider to signify it's at the desired value. At the moment, I have no way of knowing when that's the case; the action method is just getting called continuously with no indication of when the slider has been released.

If possible, I need a solution which will cover edge cases such as the user interacting the with slider with the keyboard or accessibility tools (if there is such a thing). I'd started to look into using mouse events, but it didn't seem like an optimum solution for the reasons I've just outlined.

Answer 1

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
    }
}