Scroll Wheel event capture in a Catalyst-converted Mac app

Question

When working with a Mac app which was converted from iOS using Catalyst, the usual ways to capture a mouse's scroll wheel activity for Mac such as with

• (void)scrollWheel:(NSEvent *)event;

do not work as NSEvent apparently is not supported when building a Catalyst converted app.

The object I need to control is in a regular image container and not in a scroll view container. I am simply trying to use the scroll wheel to change the loaded image. Trackpad activity works fine but capturing the scroll wheel so far has been elusive.

Thanks!

Answer 1

Use a UIPanGestureRecognizer with allowedScrollTypesMask set to UIScrollTypeMaskDiscrete:

    // pan gesture to recognize mouse-wheel scrolling (zoom)
    UIPanGestureRecognizer * scrollWheelGesture = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handleScrollWheelGesture:)];
    scrollWheelGesture.allowedScrollTypesMask = UIScrollTypeMaskDiscrete;   // only accept scroll-wheel, not track-pad
    scrollWheelGesture.maximumNumberOfTouches = 0;
    [self.view addGestureRecognizer:scrollWheelGesture];

and then

- (void)handleScrollWheelGesture:(UIPanGestureRecognizer *)pan
{
    CGPoint delta = [pan translationInView:self.view];
    CGFloat zoom = (1000 + delta.y) / 1000;
    [self adjustZoomBy:zoom];
}