How to disable horizontal scrolling of UIScrollView?

You have to set the contentSize property of the UIScrollView. For example, if your UIScrollView is 320 pixels wide (the width of the screen), then you could do this:

CGSize scrollableSize = CGSizeMake(320, myScrollableHeight);
[myScrollView setContentSize:scrollableSize];

The UIScrollView will then only scroll vertically, because it can already display everything horizontally.

In my case, with Swift 4.2 you can use:

Disable vertical scroll:

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    scrollView.contentOffset.y = 0.0
}

Disable horizontal scroll:

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    scrollView.contentOffset.x = 0.0
}

In my case the width of the contentView was greater than the width of UIScrollView and that was the reason for unwanted horizontal scrolling. I solved it by setting the width of contentView equal to width of UIScrollView.

Hope it helps someone

Introduced in iOS 11 is a new property on UIScrollView

var contentLayoutGuide: UILayoutGuide

The documentation states that you:

Use this layout guide when you want to create Auto Layout constraints related to the content area of a scroll view.

Along with any other Autolayout constraints that you might be adding you will want to constrain the widthAnchor of the UIScrollView's contentLayoutGuide to be the same size as the "frame". You can use the frameLayoutGuide (also introduced in iOS 11) or any external width (such as your superView's.)

example:

NSLayoutConstraint.activate([
  scrollView.contentLayoutGuide.widthAnchor.constraint(equalTo: self.widthAnchor)
])

Documentation: https://developer.apple.com/documentation/uikit/uiscrollview/2865870-contentlayoutguide

@Gulfam Khan's answer is the correct one, I am adding imagery to help the concept get more visibility.

When we set the contentView to have equal width's with the Scroll view, if the multiplier is even slightly greater than 1:1, then we will get horizontal scrolling.

Here is what it produces:

If you do not want horizontal scrolling, you most likely do not have horizontal content that exceeds the width of the superview.

Therefore if you ensure the contentView width does not exceed the width of the scroll view, that will automatically resolve the problem as UIKit recognizes there is no horizontal content to scroll to. Like so:

Now you should only see vertical:

Disable horizontal scrolling by overriding contentOffset property in subclass.

override var contentOffset: CGPoint {
  get {
    return super.contentOffset
  }
  set {
    super.contentOffset = CGPoint(x: 0, y: newValue.y)
  }
}

Use this single line.

self.automaticallyAdjustsScrollViewInsets = NO;