这个错误告诉你，刷新没有初始化。注意，你选择使refresh不是可选的，这在Swift中意味着它必须在调用super之前有一个值。Init(或者隐式调用，这似乎是你的情况)。要么使刷新是可选的(可能是你想要的)，要么以某种方式初始化它。

我建议你再读一遍Swift的介绍文档，里面详细地介绍了这一点。

最后，正如@Anil指出的，iOS中有一个内置的名为UIRefresControl的拉刷新控件，这可能是值得研究的东西。

斯威夫特5

private var pullControl = UIRefreshControl()

pullControl.attributedTitle = NSAttributedString(string: "Pull to refresh")
        pullControl.addTarget(self, action: #selector(refreshListData(_:)), for: .valueChanged)
        if #available(iOS 10.0, *) {
            tableView.refreshControl = pullControl
        } else {
            tableView.addSubview(pullControl)
        }
// Actions
@objc private func refreshListData(_ sender: Any) {
        self.pullControl.endRefreshing() // You can stop after API Call
        // Call API
    }

细节

Xcode版本10.3 (10G8)， Swift 5

特性

能够使“拉刷新”编程 保护从多个“拉刷新”事件 当视图控制器切换(例如在TabController的情况下)时，继续动画活动指示器的能力

解决方案

import UIKit

class RefreshControl: UIRefreshControl {

    private weak var actionTarget: AnyObject?
    private var actionSelector: Selector?
    override init() { super.init() }

    convenience init(actionTarget: AnyObject?, actionSelector: Selector) {
        self.init()
        self.actionTarget = actionTarget
        self.actionSelector = actionSelector
        addTarget()
    }

    private func addTarget() {
        guard let actionTarget = actionTarget, let actionSelector = actionSelector else { return }
        addTarget(actionTarget, action: actionSelector, for: .valueChanged)
    }

    required init?(coder aDecoder: NSCoder) { super.init(coder: aDecoder) }

    func endRefreshing(deadline: DispatchTime? = nil) {
        guard let deadline = deadline else { endRefreshing(); return }
        DispatchQueue.global(qos: .default).asyncAfter(deadline: deadline) { [weak self] in
            DispatchQueue.main.async { self?.endRefreshing() }
        }
    }

    func refreshActivityIndicatorView() {
        guard let selector = actionSelector else { return }
        let _isRefreshing = isRefreshing
        removeTarget(actionTarget, action: selector, for: .valueChanged)
        endRefreshing()
        if _isRefreshing { beginRefreshing() }
        addTarget()
    }

    func generateRefreshEvent() {
        beginRefreshing()
        sendActions(for: .valueChanged)
    }
}

public extension UIScrollView {

    private var _refreshControl: RefreshControl? { return refreshControl as? RefreshControl }

    func addRefreshControll(actionTarget: AnyObject?, action: Selector, replaceIfExist: Bool = false) {
        if !replaceIfExist && refreshControl != nil { return }
        refreshControl = RefreshControl(actionTarget: actionTarget, actionSelector: action)
    }

    func scrollToTopAndShowRunningRefreshControl(changeContentOffsetWithAnimation: Bool = false) {
        _refreshControl?.refreshActivityIndicatorView()
        guard   let refreshControl = refreshControl,
                contentOffset.y != -refreshControl.frame.height else { return }
        setContentOffset(CGPoint(x: 0, y: -refreshControl.frame.height), animated: changeContentOffsetWithAnimation)
    }

    private var canStartRefreshing: Bool {
        guard let refreshControl = refreshControl, !refreshControl.isRefreshing else { return false }
        return true
    }

    func startRefreshing() {
        guard canStartRefreshing else { return }
        _refreshControl?.generateRefreshEvent()
    }

    func pullAndRefresh() {
        guard canStartRefreshing else { return }
        scrollToTopAndShowRunningRefreshControl(changeContentOffsetWithAnimation: true)
        _refreshControl?.generateRefreshEvent()
    }

    func endRefreshing(deadline: DispatchTime? = nil) { _refreshControl?.endRefreshing(deadline: deadline) }
}

使用

// Add refresh control to UICollectionView / UITableView / UIScrollView
private func setupTableView() {
    let tableView = UITableView()
    // ...
    tableView.addRefreshControll(actionTarget: self, action: #selector(refreshData))
}

@objc func refreshData(_ refreshControl: UIRefreshControl) {
    tableView?.endRefreshing(deadline: .now() + .seconds(3))
}

// Stop refreshing in UICollectionView / UITableView / UIScrollView
tableView.endRefreshing()

// Simulate pull to refresh in UICollectionView / UITableView / UIScrollView
tableView.pullAndRefresh()

完整的样品

不要忘记在这里添加解决方案代码

import UIKit

class ViewController: UIViewController {

    private weak var tableView: UITableView?

    override func viewDidLoad() {
        super.viewDidLoad()
        setupTableView()
    }

    private func setupTableView() {
        let tableView = UITableView()
        view.addSubview(tableView)
        tableView.translatesAutoresizingMaskIntoConstraints = false
        tableView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
        tableView.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
        tableView.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true
        tableView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
        tableView.dataSource = self
        tableView.delegate = self
        tableView.addRefreshControll(actionTarget: self, action: #selector(refreshData))
        self.tableView = tableView
    }
}

extension ViewController {
    @objc func refreshData(_ refreshControl: UIRefreshControl) {
        print("refreshing")
        tableView?.endRefreshing(deadline: .now() + .seconds(3))
    }
}

extension ViewController: UITableViewDataSource {
    func numberOfSections(in tableView: UITableView) -> Int { return 1 }
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int { return 20 }
    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = UITableViewCell()
        cell.textLabel?.text = "\(indexPath)"
        return cell
    }
}

extension ViewController: UITableViewDelegate {
    func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        tableView.pullAndRefresh()
    }
}

我建议在每个类中使用pull to Refresh的扩展。

1)创建一个空的swift文件:文件-新建-文件- swift文件。

2)添加以下内容

    //  AppExtensions.swift

    import Foundation
    import UIKit    

    var tableRefreshControl:UIRefreshControl = UIRefreshControl()    

    //MARK:- VIEWCONTROLLER EXTENSION METHODS
    public extension UIViewController
    {
        func makePullToRefreshToTableView(tableName: UITableView,triggerToMethodName: String){

            tableRefreshControl.attributedTitle = NSAttributedString(string: "TEST: Pull to refresh")
            tableRefreshControl.backgroundColor = UIColor.whiteColor()
            tableRefreshControl.addTarget(self, action: Selector(triggerToMethodName), forControlEvents: UIControlEvents.ValueChanged)
            tableName.addSubview(tableRefreshControl)
        }
        func makePullToRefreshEndRefreshing (tableName: String)
        {
            tableRefreshControl.endRefreshing()
//additional codes

        }
    }    

3)在你的视图控制器中调用这些方法:

  override func viewWillAppear(animated: Bool) {

self.makePullToRefreshToTableView(bidderListTable, triggerToMethodName: "pullToRefreshBidderTable")
}

4)在某些时候，你想要结束刷新:

  func pullToRefreshBidderTable() {
self.makePullToRefreshEndRefreshing("bidderListTable")    
//Code What to do here.
}
OR    
self.makePullToRefreshEndRefreshing("bidderListTable")

使用storyboard和Swift的解决方案:

Open your .storyboard file, select a TableViewController in your storyboard and "Enable" the Table View Controller: Refreshing feature in the Utilities. Open the associated UITableViewController class and add the following Swift 5 line into the viewDidLoad method. self.refreshControl?.addTarget(self, action: #selector(refresh), for: UIControl.Event.valueChanged) Add the following method above the viewDidLoad method func refresh(sender:AnyObject) { // Updating your data here... self.tableView.reloadData() self.refreshControl?.endRefreshing() }

UIRefreshControl直接支持在每个UICollectionView, UITableView和UIScrollView(需要iOS 10+)!

这些视图中的每一个都有一个refreshControl实例属性，这意味着不再需要在你的滚动视图中添加它作为子视图，你所要做的就是:

@IBOutlet weak var collectionView: UICollectionView!

override func viewDidLoad() {
    super.viewDidLoad()
    
    let refreshControl = UIRefreshControl()
    refreshControl.addTarget(self, action: #selector(doSomething), for: .valueChanged)
    
    // this is the replacement of implementing: "collectionView.addSubview(refreshControl)"
    collectionView.refreshControl = refreshControl
}

@objc func doSomething(refreshControl: UIRefreshControl) {
    print("Hello World!")
    
    // somewhere in your code you might need to call:
    refreshControl.endRefreshing()
}

就我个人而言，我觉得将它作为滚动视图的属性比将它作为子视图添加更自然，特别是因为唯一合适的视图作为UIRefreshControl的父视图是一个滚动视图，即使用UIRefreshControl的功能只在与滚动视图一起工作时有用;这就是为什么这种方法应该更明显地设置刷新控件视图。

但是，你仍然可以选择基于iOS版本使用addSubview:

if #available(iOS 10.0, *) {
  collectionView.refreshControl = refreshControl
} else {
  collectionView.addSubview(refreshControl)
}