和一个UICollectionView版本，基于kolaworld的答案。

它需要测试。到目前为止，它在iOS 9.2和Xcode 9.2 beta 2上工作，将collectionView滚动到一个索引，作为一个闭包。

extension UICollectionView
{
    /// Calls reloadsData() on self, and ensures that the given closure is
    /// called after reloadData() has been completed.
    ///
    /// Discussion: reloadData() appears to be asynchronous. i.e. the
    /// reloading actually happens during the next layout pass. So, doing
    /// things like scrolling the collectionView immediately after a
    /// call to reloadData() can cause trouble.
    ///
    /// This method uses CATransaction to schedule the closure.

    func reloadDataThenPerform(_ closure: @escaping (() -> Void))
    {
        CATransaction.begin()
            CATransaction.setCompletionBlock(closure)
            self.reloadData()
        CATransaction.commit()
    }
}

用法:

myCollectionView.reloadDataThenPerform {
    myCollectionView.scrollToItem(at: indexPath,
            at: .centeredVertically,
            animated: true)
}

和一个UICollectionView版本，基于kolaworld的答案。

它需要测试。到目前为止，它在iOS 9.2和Xcode 9.2 beta 2上工作，将collectionView滚动到一个索引，作为一个闭包。

extension UICollectionView
{
    /// Calls reloadsData() on self, and ensures that the given closure is
    /// called after reloadData() has been completed.
    ///
    /// Discussion: reloadData() appears to be asynchronous. i.e. the
    /// reloading actually happens during the next layout pass. So, doing
    /// things like scrolling the collectionView immediately after a
    /// call to reloadData() can cause trouble.
    ///
    /// This method uses CATransaction to schedule the closure.

    func reloadDataThenPerform(_ closure: @escaping (() -> Void))
    {
        CATransaction.begin()
            CATransaction.setCompletionBlock(closure)
            self.reloadData()
        CATransaction.commit()
    }
}

用法:

myCollectionView.reloadDataThenPerform {
    myCollectionView.scrollToItem(at: indexPath,
            at: .centeredVertically,
            animated: true)
}

试试这个方法。它会起作用的。

[tblViewTerms performSelectorOnMainThread:@selector(dataLoadDoneWithLastTermIndex:) withObject:lastTermIndex waitUntilDone:YES];waitUntilDone:YES];

@interface UITableView (TableViewCompletion)

-(void)dataLoadDoneWithLastTermIndex:(NSNumber*)lastTermIndex;

@end

@implementation UITableView(TableViewCompletion)

-(void)dataLoadDoneWithLastTermIndex:(NSNumber*)lastTermIndex
{
    NSLog(@"dataLoadDone");

NSIndexPath* indexPath = [NSIndexPath indexPathForRow: [lastTermIndex integerValue] inSection: 0];

[self selectRowAtIndexPath:indexPath animated:YES scrollPosition:UITableViewScrollPositionNone];

}
@end

我将在表完全加载时执行。

另一个解决方案是你可以子类化UITableView。

细节

Xcode版本10.2.1 (10E1001)， Swift 5

解决方案

import UIKit

// MARK: - UITableView reloading functions

protocol ReloadCompletable: class { func reloadData() }

extension ReloadCompletable {
    func run(transaction closure: (() -> Void)?, completion: (() -> Void)?) {
        guard let closure = closure else { return }
        CATransaction.begin()
        CATransaction.setCompletionBlock(completion)
        closure()
        CATransaction.commit()
    }

    func run(transaction closure: (() -> Void)?, completion: ((Self) -> Void)?) {
        run(transaction: closure) { [weak self] in
            guard let self = self else { return }
            completion?(self)
        }
    }

    func reloadData(completion closure: ((Self) -> Void)?) {
        run(transaction: { [weak self] in self?.reloadData() }, completion: closure)
    }
}

// MARK: - UITableView reloading functions

extension ReloadCompletable where Self: UITableView {
    func reloadRows(at indexPaths: [IndexPath], with animation: UITableView.RowAnimation, completion closure: ((Self) -> Void)?) {
        run(transaction: { [weak self] in self?.reloadRows(at: indexPaths, with: animation) }, completion: closure)
    }

    func reloadSections(_ sections: IndexSet, with animation: UITableView.RowAnimation, completion closure: ((Self) -> Void)?) {
        run(transaction: { [weak self] in self?.reloadSections(sections, with: animation) }, completion: closure)
    }
}

// MARK: - UICollectionView reloading functions

extension ReloadCompletable where Self: UICollectionView {

    func reloadSections(_ sections: IndexSet, completion closure: ((Self) -> Void)?) {
        run(transaction: { [weak self] in self?.reloadSections(sections) }, completion: closure)
    }

    func reloadItems(at indexPaths: [IndexPath], completion closure: ((Self) -> Void)?) {
        run(transaction: { [weak self] in self?.reloadItems(at: indexPaths) }, completion: closure)
    }
}

使用

UITableView

// Activate
extension UITableView: ReloadCompletable { }

// ......
let tableView = UICollectionView()

// reload data
tableView.reloadData { tableView in print(collectionView) }

// or
tableView.reloadRows(at: indexPathsToReload, with: rowAnimation) { tableView in print(tableView) }

// or
tableView.reloadSections(IndexSet(integer: 0), with: rowAnimation) { _tableView in print(tableView) }

UICollectionView

// Activate
extension UICollectionView: ReloadCompletable { }

// ......
let collectionView = UICollectionView()

// reload data
collectionView.reloadData { collectionView in print(collectionView) }

// or
collectionView.reloadItems(at: indexPathsToReload) { collectionView in print(collectionView) }

// or
collectionView.reloadSections(IndexSet(integer: 0)) { collectionView in print(collectionView) }

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 navigationBar: UINavigationBar?
    private weak var tableView: UITableView?

    override func viewDidLoad() {
        super.viewDidLoad()
        setupNavigationItem()
        setupTableView()
    }
}
// MARK: - Activate UITableView reloadData with completion functions

extension UITableView: ReloadCompletable { }

// MARK: - Setup(init) subviews

extension ViewController {

    private func setupTableView() {
        guard let navigationBar = navigationBar else { return }
        let tableView = UITableView()
        view.addSubview(tableView)
        tableView.translatesAutoresizingMaskIntoConstraints = false
        tableView.topAnchor.constraint(equalTo: navigationBar.bottomAnchor).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
        self.tableView = tableView
    }

    private func setupNavigationItem() {
        let navigationBar = UINavigationBar()
        view.addSubview(navigationBar)
        self.navigationBar = navigationBar
        navigationBar.translatesAutoresizingMaskIntoConstraints = false
        navigationBar.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor).isActive = true
        navigationBar.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
        navigationBar.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true
        let navigationItem = UINavigationItem()
        navigationItem.rightBarButtonItem = UIBarButtonItem(title: "all", style: .plain, target: self, action: #selector(reloadAllCellsButtonTouchedUpInside(source:)))
        let buttons: [UIBarButtonItem] = [
                                            .init(title: "row", style: .plain, target: self,
                                                  action: #selector(reloadRowButtonTouchedUpInside(source:))),
                                            .init(title: "section", style: .plain, target: self,
                                                  action: #selector(reloadSectionButtonTouchedUpInside(source:)))
                                            ]
        navigationItem.leftBarButtonItems = buttons
        navigationBar.items = [navigationItem]
    }
}

// MARK: - Buttons actions

extension ViewController {

    @objc func reloadAllCellsButtonTouchedUpInside(source: UIBarButtonItem) {
        let elementsName = "Data"
        print("-- Reloading \(elementsName) started")
        tableView?.reloadData { taleView in
            print("-- Reloading \(elementsName) stopped \(taleView)")
        }
    }

    private var randomRowAnimation: UITableView.RowAnimation {
        return UITableView.RowAnimation(rawValue: (0...6).randomElement() ?? 0) ?? UITableView.RowAnimation.automatic
    }

    @objc func reloadRowButtonTouchedUpInside(source: UIBarButtonItem) {
        guard let tableView = tableView else { return }
        let elementsName = "Rows"
        print("-- Reloading \(elementsName) started")
        let indexPathToReload = tableView.indexPathsForVisibleRows?.randomElement() ?? IndexPath(row: 0, section: 0)
        tableView.reloadRows(at: [indexPathToReload], with: randomRowAnimation) { _tableView in
            //print("-- \(taleView)")
            print("-- Reloading \(elementsName) stopped in \(_tableView)")
        }
    }

    @objc func reloadSectionButtonTouchedUpInside(source: UIBarButtonItem) {
        guard let tableView = tableView else { return }
        let elementsName = "Sections"
        print("-- Reloading \(elementsName) started")
        tableView.reloadSections(IndexSet(integer: 0), with: randomRowAnimation) { _tableView in
            //print("-- \(taleView)")
            print("-- Reloading \(elementsName) stopped in \(_tableView)")
        }
    }
}

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 = "\(Date())"
        return cell
    }
}

结果

如果你在viewDidLoad时重新加载数据，你可以把你的代码放到viewDidLayoutSubviews方法中。但是你应该小心viewDidLayoutSubviews可能会被多次调用。

创建CATransaction的可重用扩展:

public extension CATransaction {
    static func perform(method: () -> Void, completion: @escaping () -> Void) {
        begin()
        setCompletionBlock {
            completion()
        }
        method()
        commit()
    }
}

现在创建一个UITableView的扩展，使用CATransaction的扩展方法:

public extension UITableView {
    func reloadData(completion: @escaping (() -> Void)) {
       CATransaction.perform(method: {
           reloadData()
       }, completion: completion)
    }
}

用法:

tableView.reloadData(completion: {
    //Do the stuff
})