UITableView分页，将无限显示加载

Question

我正在尝试在我的应用程序中实现一个聊天功能，该功能将模仿iMessages的拉动以加载更多消息。我的 API 在每次调用中发送 20 条消息以及 pageIndex 和其他值来跟踪页面和消息。

我正在使用 TableView 将显示和拉取以刷新功能来实现分页。

我无法添加正确的逻辑来在 willDisplay 中加载更多消息，并且它会进入无限循环。任何人都可以通过查看下面的代码来指出我正确的方向吗？

import UIKit
class ChatViewController: UIViewController, UITableViewDelegate, UITableViewDataSource, UITextViewDelegate  {
@IBOutlet weak var messagesTable: UITableView!
@IBOutlet weak var activityIndicator: UIActivityIndicatorView!
var messages: Messages!
var messageArray = [Message]()
// Pagination
var isLoading = false
var pageSize = 10
var totalPages: Int!
var currentPage: Int!
// Pull To Refresh
let refreshControl = UIRefreshControl()
override func viewWillAppear(_ animated: Bool){
super.viewWillAppear(animated)
activityIndicator.startAnimating()
fetchMessages(page: 1, completed: {
self.totalPages = self.messages.pageCount
self.currentPage = self.messages.currentPage
// Sort message by ID so that latest message appear at the bottom.
self.messageArray = self.messages.messages!.sorted(by: {$0.id! < $1.id!})
self.messagesTable.reloadData()
// Scroll to the bottom of table
self.messagesTable.scrollToBottom(animated: false)
self.activityIndicator.stopAnimating()
})
}
// MARK: - Table view data source
func numberOfSections(in tableView: UITableView) -> Int {
return 1
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return messageArray.count
}
func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
if !self.isLoading && indexPath.row == 0 {
self.isLoading = true
fetchMessages(page: self.currentPage, completed: {
if self.currentPage == 0 {
self.messageArray.removeAll()
}
self.messageArray.append(contentsOf: self.messages!.messages!)
self.messageArray = self.messageArray.sorted(by: {$0.id! < $1.id!})
self.messagesTable.reloadData()
// Scroll to the top
self.messagesTable.scrollToRow(at: indexPath, at: UITableViewScrollPosition.top, animated: true)
self.currentPage = self.currentPage + 1
})
self.isLoading = false
}
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
guard let cell = tableView.dequeueReusableCell(withIdentifier: "MessageCell", for: indexPath) as? MessageCell else {
fatalError("Can't find cell")
}
return cell
}

private func fetchMessages(page: Int, completed: @escaping () -> ()){
guard let url = URL(string: "http://example.com/....") else { return }
URLSession.shared.dataTask(with: url) { (data, response, error) in
if error != nil {
print("Error in fetching data..........")
print(error!.localizedDescription)
}
guard let data = data else { return }
if let str = String(data: data, encoding: .utf8) { print(str) }
do {
let resultData = try JSONDecoder().decode(messagesStruct.self, from: data)
DispatchQueue.main.async {
print("DispatchQueue.main.async")
self.messages = resultData.data!
completed()
}
} catch let jsonError {
print(jsonError)
}
}.resume()
}
//Pull to refresh
@objc func refresh(_ refreshControl: UIRefreshControl) {
fetchMessages(completed: {
self.messagesTable.reloadData()
})
refreshControl.endRefreshing()
}

}

Answer 1

willDisplayCell

不是检查tableView是否实际滚动到底部的安全位置，而是使用scrollViewDelegate

func scrollViewDidScroll(_ scrollView: UIScrollView) {
if !self.isLoading && (messagesTable.contentOffset.y >= (messagesTable.contentSize.height - messagesTable.frame.size.height)) {
self.isLoading = true
fetchMessages(page: self.currentPage, completed: {[weak self]
guard let strongSelf = self else {
return
}
strongSelf.isLoading = false
if strongSelf.currentPage == 0 {
strongSelf.messageArray.removeAll()
}
strongSelf.messageArray.append(contentsOf: strongSelf.messages!.messages!)
strongSelf.messageArray = strongSelf.messageArray.sorted(by: {$0.id! < $1.id!})
strongSelf.messagesTable.reloadData()
strongSelf.currentPage = strongSelf.currentPage + 1
})
}
}

希望对你有帮助