How to stop a UIScrollView at a specific point?

Question

How do you stop a UIScrollView at specific point? That is, set the final position of the UIScrollView after user interaction?

Specifically, how can you set intervals along a horizontal UIScrollView, so that the it will only stop at these points?

I hope what I have said is clear enough.

Solution 1

Take a look at method scrollViewWillEndDragging:withVelocity:targetContentOffset: of UIScrollViewDelegate. It's intended to do exactly what you need.

The scroll view sends this message to its delegate when the user finishes dragging the scroll view. The third parameter (targetContentOffset) is passed as a pointer, and you can change its value to change where the scroll view will stop.

iOS 5.0 and later.

Solution 2

You've got 3 options:

1. You can do so using pagingEnabled.
   
   
2. Use setContentOffset: animated: in the UIScrollViewDelegate scrollViewDidEndDecelerating: method
   
   
3. Create your own scroll view using touchesBegan, touchesMoved and touchesEnded and extrapolate to create momentum with a appropriate endpoint

Solution 3

I've found something that works for me. It let's you scroll to point 0,0 but no further:

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    if (scrollView.contentOffset.x <= -1) {
        [scrollView setScrollEnabled:NO];
        [self.scrollView setContentOffset:CGPointMake(0, 0) animated:YES];
        [scrollView setScrollEnabled:YES];
    }
}

You could do the same for top, bottom or right (x or y)

Solution 4

to achieve this u need to enable the paging of the scrollview

For example:

[scrollView setContentSize:CGSizeMake(640, 161)];
[scrollView setPagingEnabled:YES];

here, width of scrollview is 640 (twice of width of iphone screen), if paging is enabled it will divide it equally depending on the width. So as we scroll to this position it will stop at the particular offset.

Solution 5

For those we need to set the targetContentOffset in Swift like rob mayoff says in his excellent answer above , this is the way :

func scrollViewWillEndDragging(scrollView: UIScrollView!, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
    targetContentOffset.memory.y = x 
}

View more solutions

Comments

[Jesse Head]

yeah... i looked at that originally, but i want to allow my content to stop at any number of positions after a swipe. paging only allows one set distance to be moved per swipe (in this case 320 pixels i believe?). this is hard to explain... if you have a look at the free news app called 'pulse' it shows what i am after.

[vishy]

actually if the content size of scrollview is more then screen size, user can set to the fixed position as scrolling horiz/vert... do u want to do this by code..?

[vishy]

u can do by implementing its delegate methods, & using its offset value u can have either scroll more or stop scrolling...

[vishy]

use - (void)setContentOffset:(CGPoint)contentOffset animated:(BOOL)animated to scroll by code to a fixed position (offset), calculate the exact offset required..

[Jesse Head]

ahh yeah, but wouldn't a separate event have to occur for the above method to be triggered? i want it to occur automatically after the scrolling has ended.

[Jesse Head]

Finally someone is starting to understand what I'm looking for lol. number 2 is looking pretty appealing. will see how it works.

[Jesse Head]

Would you know how to detect the current position of the scrollview as the scrollViewDidEndDecelerating: method is triggered?

[vishy]

in didscrollend delegate u can do this... go through the delegate methods list once...

[basvk]

The current position is stored in the contentOffset (CGPoint) property

[SleepNot]

@JesseHead what did you end up using?

[G.Abhisek]

@JesseHead So what was your final answer?

[Fattie]

note that in many cases, you will also use scrollViewDidScroll - so that, the value will change as the user holds-and-moves the slider.

[Admin]

Helped me out a ton!

[budiDino]

for other n00bs like me, you can change targetContentOffset by updating targetContentOffset.pointee to a new CGPoint value ;)