Question

I’m having some images from which the user should choose one. Now I don’t want to just offer an flat scrolling area with a boring grid. Instead, I’d like to show up a wheel that contains those images. At the top would be a marker indicating the selection. Something similar to the Pickers.

The problem is not the rotation stuff; I’d use some geometric functions for that. But I have no idea how to actually get the scrolling gestures on that wheel. Where must I start?

BTW: With circular I don’t mean something like the Pickers. I mean a real wheel that has a center axis and can be rolled. Like the very old telephones, like a bike wheel. Or a Picker turned by 90°, facing with the axis to you (Z-coordinate).

Answer 1

If you’re talking about capturing gestures then here is the example they give in the docs.

Though I could have sworn I heard Alan Cannistraro say in one of the first CS193P lectures that you don’t have to do this, that you can just trap the swipe event but I can’t find that.

Could someone that actually knows what they are doing please correct me and I’ll remove this post but for now I know this will work:

#define HORIZ_SWIPE_DRAG_MIN  12
#define VERT_SWIPE_DRAG_MAX    4

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [touches anyObject];
    startTouchPosition = [touch locationInView:self];
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [touches anyObject];
    CGPoint currentTouchPosition = [touch locationInView:self];

    // If the swipe tracks correctly.
    if (fabsf(startTouchPosition.x - currentTouchPosition.x) >= HORIZ_SWIPE_DRAG_MIN &&
        fabsf(startTouchPosition.y - currentTouchPosition.y) <= VERT_SWIPE_DRAG_MAX)
    {
        // It appears to be a swipe.
        if (startTouchPosition.x < currentTouchPosition.x)
            [self myProcessRightSwipe:touches withEvent:event];
        else
            [self myProcessLeftSwipe:touches withEvent:event];
    }
    else
    {
        // Process a non-swipe event.
    }
}