How to add ScrollView in iOS?

iOS devices have limited screen sizes, so it’s common that the content you want to display is larger than the available space. The scroll view is an essential component for enabling scrolling in iOS apps. With a scroll view, users can scroll through content that is larger than the screen size. In this article, we will go over how to add and configure a scroll view in an iOS app.

What is a ScrollView in iOS?

A scroll view (UIScrollView) is a view that enables scrolling through content that is larger than the view’s frame. With a scroll view, you can display content that extends well beyond the borders of the screen. Some key features of scroll views:

• Allows scrolling vertically, horizontally, or both
• Supports paging for horizontal scroll views
• Can contain multiple subviews
• Provides built-in gesture recognizers for scrolling
• Manages scrolling behavior and momentum scrolling

Scroll views are ideal for showing lists, documents, web content, and other apps that require extensive scrolling. You can add various UI elements as subviews of a scroll view, like images, text, buttons, etc. The scroll view handles the scrolling so you don’t have to implement it yourself.

Adding a Scroll View in Storyboard

The easiest way to add a scroll view is using the storyboard in Xcode. Here are the steps:

1. Open Main.storyboard and drag a Scroll View from the object library onto the View Controller.
2. Resize the scroll view to match the size of the view controller.
3. Add subviews into the scroll view, like labels, images, etc. Make sure the subviews are large so that scrolling is required.
4. Add appropriate constraints to position the subviews.
5. Control-drag from the scroll view to the view controller code to create an outlet named scrollView.

That’s all you need to get a basic scroll view working in the storyboard! The key is making sure the content inside the scroll view is larger than the scroll view frame so that scrolling is required.

Programmatically Adding a Scroll View

You can also programmatically create and add a scroll view without using the storyboard. Here is an example:

// Create the scroll view
let scrollView = UIScrollView(frame: view.bounds)

// Configure scroll view  
scrollView.contentSize = CGSize(width: 1000, height: 1000)
        
// Add scroll view as a subview 
view.addSubview(scrollView)

Some key points:

• Initialize the scroll view with the view controller’s view bounds
• Set the contentSize property to define the scrolling size
• Add as a subview to the main view

You still need to add subviews and constraints just like in the storyboard approach. Programmatic is useful for dynamic scroll views whose content changes.

Setting Scroll View Delegate

To get information about scrolling events and position, you need to set the scroll view’s delegate. This is typically the view controller.

class ViewController: UIViewController, UIScrollViewDelegate {

  override func viewDidLoad() {
    super.viewDidLoad()
        
    scrollView.delegate = self
  }

}  

Implement scroll view delegate methods to get callbacks for events like scrolling, dragging, decelerating, and more.

Configuring Scroll View Behavior

There are several properties on UIScrollView to control scrolling behavior:

• isDirectionalLockEnabled – Locks scrolling to vertical or horizontal axis.
• bounces – Enables bounce animations when stopping scroll.
• alwaysBounceVertical/Horizontal – Bounce at the edge of scroll view.
• scrollEnabled – Enables or disables user scrolling.
• decelerationRate – Rate of deceleration when stopping scroll.

For example, to disable horizontal scrolling:

scrollView.isDirectionalLockEnabled = true
scrollView.directionalLockEnabled = .vertical

Implementing Paging

For horizontal scroll views, you can enable paging which snaps scroll positions to pages. To enable:

• Set pagingEnabled to true
• Set scroll indicator insets for spacing between pages
• Calculate contentSize based on pages

// Paging example
scrollView.pagingEnabled = true
scrollView.scrollIndicatorInsets = UIEdgeInsets(top: 0, left: 10, bottom: 0, right: 10)

let pageWidth = view.frame.width
scrollView.contentSize = CGSize(width: pageWidth * 3, height: view.frame.height) 

This allows scrolling horizontally between 3 page views. The insets add spacing between the pages.

Tracking Scroll Position

There are several ways to track the scroll position:

• Scroll view delegate methods like scrollViewDidScroll
• UIScrollView properties like contentOffset, contentSize
• Observe UIScrollView.frame changes with KVO

For example, to get content offset:

func scrollViewDidScroll(_ scrollView: UIScrollView) {
  let offset = scrollView.contentOffset
  print("Content offset: \(offset)")
}

You can use the scroll position to load additional content, change headers, update page controls, etc.

Troubleshooting Tips

Some common issues when working with scroll views:

• No scrolling – Check that contentSize is larger than frame
• White space – Constrain subviews to scroll view edges
• Unexpected bouncing – Set bounces and alwaysBounce properties appropriately
• Lack of precision – Use delegates over KVO for accuracy
• Slow scrolling – Use constraints instead of frames for subviews

Setting the contentSize correctly is key to getting scroll views working properly. The content size dictates how large the scrolling area is so it must exceed the scroll view frame to enable scrolling.

Conclusion

Here are some key points about working with scroll views in iOS:

• Add scroll view in Storyboard or programmatically
• Set contentSize bigger than frame size
• Configure behavior with properties like paging, scroll indicator insets, etc.
• Use delegate methods for scrolling events and positioning
• Size and constraint subviews properly to avoid issues

Scroll views are essential for providing scrolling functionality on iOS. They handle all the complexities around touch tracking, scrolling physics, and scrolling gestures. With the properties and delegate methods on UIScrollView, you can have full control over the scrolling behavior. Mastering scroll views will let you create robust, high quality scrolling experiences in your iOS apps.