Deactivate UIScrollView decelerating

问题

Is there a way to deactivate the decelerating of a UIScrollView?

I want to allow the user to scroll the canvas, but I don't want that the canvas continues scrolling after the user lifted the finger.

回答1:

This can be done by utilizing the UIScrollView delegate method scrollViewWillBeginDecelerating to automatically set the content offset to the current screen position.

To implement:

Assign a delegate to your UIScrollView object if you have not already done so.

In your delegate's .m implementation file, add the following lines of code:

-(void)scrollViewWillBeginDecelerating:(UIScrollView *)scrollView{  
    [scrollView setContentOffset:scrollView.contentOffset animated:YES];   
}

Voila! No more auto-scroll.

回答2:

For iOS 5.0 or later, there is a better method than calling setContentOffset:animated:.

Implement delegate method scrollViewWillEndDragging:withVelocity:targetContentOffset: in your .m file:

- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView
                     withVelocity:(CGPoint)velocity
              targetContentOffset:(inout CGPoint *)targetContentOffset {
    *targetContentOffset = scrollView.contentOffset;
}

Assigning the current offset to targetContentOffset stops the UIScrollView from auto-scrolling.

回答3:

You can just turn up the deceleration rate very high. With an infinite rate, it would stop immediately. Try setting the rate to these constants:

scrollView.decelerationRate = UIScrollViewDecelerationRateNormal;

and

scrollView.decelerationRate = UIScrollViewDecelerationRateFast;

If fast still isn't fast enough for you, UIScrollViewDecelerationRateFast is just typedef'ed as a float, so you can just multiply it by a factor of 10 or so to speed it up even more.