Using UIRefreshControl

Pull to refresh has been a standard UI convention in iOS since early days of Twitter. It's easy to include the default pull to refresh control into any scroll view, including UIScrollView, UITableView, or UICollectionView.

Step 1: Create the UIRefreshControl

It's useful to create the UIRefreshControl as an instance variable at the top of the class because you need to access it to stop the loading behavior.

    var refreshControl: UIRefreshControl!
    
    ...

Step 2: Implement onRefresh Method

We will call this method every time the refresh control is triggered.

func onRefresh() {
   
}

Step 3: Add the UIRefreshControl to the Scroll View

In the viewDidLoad() method, add the refresh control as a subview of the scroll view. It's best to insert it at the lowest index so that it appears behind all the views in the scroll view.

    refreshControl = UIRefreshControl()
    refreshControl.addTarget(self, action: #selector(onRefresh), forControlEvents: .ValueChanged)
    scrollView.insertSubview(refreshControl, at: 0)

Note: If the above code is not compiling, it may be because you are using an older version of Xcode. In that case try:

    refreshControl = UIRefreshControl()
    refreshControl.addTarget(self, action: "onRefresh", forControlEvents: UIControlEvents.ValueChanged)
    scrollView.insertSubview(refreshControl, atIndex: 0)

Step 4: Use Delay to Simulate Network Loading

For prototyping, you can simulate network loading by canceling refreshing after a couple of seconds.

// Implement the delay method
func run(after wait: TimeInterval, closure: @escaping () -> Void) {
    let queue = DispatchQueue.main
    queue.asyncAfter(deadline: DispatchTime.now() + wait, execute: closure)
}

// Call the delay method in your onRefresh() method
func refresh() {
    run(after: 2) { 
       self.refreshControl.endRefreshing()
    }
}