iPhone UIScrollView Speed Check

Converted @bandejapaisa answer to Swift 5:

Properties used by UIScrollViewDelegate:

var lastOffset: CGPoint = .zero
var lastOffsetCapture: TimeInterval = .zero
var isScrollingFast: Bool = false

And the scrollViewDidScroll function:

func scrollViewDidScroll(scrollView: UIScrollView) {

    let currentOffset = scrollView.contentOffset
    let currentTime = Date.timeIntervalSinceReferenceDate
    let timeDiff = currentTime - lastOffsetCapture
    let captureInterval = 0.1
    
    if timeDiff > captureInterval {
        
        let distance = currentOffset.y - lastOffset.y     // calc distance
        let scrollSpeedNotAbs = (distance * 10) / 1000     // pixels per ms*10
        let scrollSpeed = fabsf(Float(scrollSpeedNotAbs))  // absolute value
        
        if scrollSpeed > 0.5 {
            isScrollingFast = true
            print("Fast")
        } else {
            isScrollingFast = false
            print("Slow")
        }
        
        lastOffset = currentOffset
        lastOffsetCapture = currentTime
        
    }
}

Have these properties on your UIScrollViewDelegate

CGPoint lastOffset;
NSTimeInterval lastOffsetCapture;
BOOL isScrollingFast;

Then have this code for your scrollViewDidScroll:

- (void) scrollViewDidScroll:(UIScrollView *)scrollView {    
    CGPoint currentOffset = scrollView.contentOffset;
    NSTimeInterval currentTime = [NSDate timeIntervalSinceReferenceDate];

    NSTimeInterval timeDiff = currentTime - lastOffsetCapture;
    if(timeDiff > 0.1) {
        CGFloat distance = currentOffset.y - lastOffset.y;
        //The multiply by 10, / 1000 isn't really necessary.......
        CGFloat scrollSpeedNotAbs = (distance * 10) / 1000; //in pixels per millisecond

        CGFloat scrollSpeed = fabsf(scrollSpeedNotAbs);
        if (scrollSpeed > 0.5) {
            isScrollingFast = YES;
            NSLog(@"Fast");
        } else {
            isScrollingFast = NO;
            NSLog(@"Slow");
        }        

        lastOffset = currentOffset;
        lastOffsetCapture = currentTime;
    }
}

And from this i'm getting pixels per millisecond, which if is greater than 0.5, i've logged as fast, and anything below is logged as slow.

I use this for loading some cells on a table view animated. It doesn't scroll so well if I load them when the user is scrolling fast.

There's an easier way: check the UISCrollview's pan gesture recognizer. With it, you can get the velocity like so:

CGPoint scrollVelocity = [[_scrollView panGestureRecognizer] velocityInView:self];