Collection View, Scroll View, Table View在iOS 10都與生俱來支援下拉更新了 !

在iOS 10，Collection View, Scroll View, Table View都與生俱來支援UIRefreshControl物件，只要三個步驟即可實現下拉更新功能:

1. 生成UIRefreshControl物件。

2. 設定UIRefreshControl物件在下拉更新時觸發的function。

3. 將UIRefreshControl物件指定到Collection View, Scroll View或Table View的refreshControl屬性。

實例:

let refreshControl = UIRefreshControl()
refreshControl.addTarget(self, action:   
     #selector(ViewController.refreshData(refreshControl:)) , 
     for: .valueChanged)
self.movieTableView.refreshControl = refreshControl

到底這refreshControl屬性是哪裡來的呢? 其實它來自protocol UIRefreshControlHosting。

public protocol UIRefreshControlHosting : NSObjectProtocol {
     public var refreshControl: UIRefreshControl? { get set }
}

UIScrollView遵從protocol UIRefreshControlHosting，而UITableView和UICollectionView皆繼承UIScrollView，因此讓Collection View, Scroll View, Table View都獲得了refreshControl屬性。