cellForRowAt indexPath未使用reloadData()方法调用

Question

在Swift 3中，我试图创建一个"Filter"视图，让用户按类别和日期过滤表视图中的帖子。目前，过滤器视图以模式显示，并在单击"完成"时被取消。

我还没有设置日期/类别功能。首先，我只是想让tableView更新为只显示帖子的3，而不是10。为此，我在FilterViewController中设置了destination.numPosts = 3。

使用print语句，可以看出TableViewController实际上在viewDidLoad函数中更新了它的posts数组，使其具有3posts。numberOfRowsInSection被调用并且是正确的。numberofSections总是返回1。在viewDidLoad中，我尝试了self.tableView.reloadData()和tableView.reloadData()，但是，cellForRowAt indexPath只有在您最初运行应用程序时才会被调用，而当数据被重新加载时，它不会调用它。

当FilterViewController被解雇时，我如何重新填写职位表，有什么想法吗？

表视图控制器：

import UIKit
class TableViewController: UITableViewController {
let myArray = ["item 1", "item 2", "item 3"]
var posts = [Post]()
var numPosts = 9
override func viewDidLoad() {
super.viewDidLoad()
self.tableView.delegate = self
self.tableView.dataSource = self
// Uncomment the following line to preserve selection between presentations
// self.clearsSelectionOnViewWillAppear = false
// Uncomment the following line to display an Edit button in the navigation bar for this view controller.
// self.navigationItem.rightBarButtonItem = self.editButtonItem()
/*
let logo = UIImage(named: "860logo.png")
let imageView = UIImageView(image:logo)
self.navigationItem.titleView = imageView
*/
var titleView: UIImageView
titleView = UIImageView(frame:CGRect(x: 0, y: 0, width: 50, height: 60))
titleView.contentMode = .scaleAspectFit
titleView.image = UIImage(named: "860logo.png")
self.navigationItem.titleView = titleView

//titleView.backgroundColor = UIColor(red:0.18, green:0.20, blue:0.38, alpha:1.0)
let newPost = Post(id: 6503, title: "Work Zone Accident", date: "2016-12-05T09:24:47", url: "http://www.mlive.com/news/ann-arbor/index.ssf/2016/12/ann_arbor_brings_charges_again.html", category: "Work Zone Accidents")
let newPost2 = Post(id: 6501, title: "Anti-Union Laws (Unemployment)", date: "2016-12-05T09:24:19", url: "http://www.cleveland.com/opinion/index.ssf/2016/12/gop_lawmakers_from_high-jobles.html#incart_river_mobile_home", category: "Anti-Union Laws")
let newPost3 = Post(id: 6499, title: "Anti-Union Appointments", date: "2016-12-05T09:23:36", url: "http://prospect.org/article/trump-labor-secretary-could-be-fight-15-worst-nightmare", category: "Anti-Union Laws")
let newPost4 = Post(id: 6497, title: "Infrastructure", date: "2016-12-05T09:23:06", url: "http://www.cbpp.org/research/federal-budget/trump-infrastructure-plan-far-less-than-the-claimed-1-trillion-in-new", category: "infrastructure")
let newPost5 = Post(id: 6495, title: "Work Zone Accident", date: "2016-12-05T09:22:38", url: "http://www.marinij.com/general-news/20161202/construction-worker-struck-by-car-in-novato", category: "Work Zone Accidents")
let newPost6 = Post(id: 6493, title: "Infrastructure", date: "2016-12-05T09:22:03", url: "http://markets.businessinsider.com/news/stocks/There-could-be-an-unexpected-side-effect-of-Trumps-infrastructure-spending-1001554657", category: "infrastructure")
let newPost7 = Post(id: 6491, title: "Infrastructure", date: "2016-12-05T09:14:28", url: "http://www.nydailynews.com/opinion/build-not-burn-bridges-infrastructure-article-1.2890434", category: "infrastructure")
let newPost8 = Post(id: 6489, title: "Highway Funding", date: "2016-12-01T11:02:55", url: "http://www.gobytrucknews.com/democrats-want-highway-funds/123", category: "Funding")
let newPost9 = Post(id: 6487, title: "Highway Funding (Congressional Bottleneck)", date: "2016-12-01T11:02:00", url: "https://www.trucks.com/2016/12/01/raise-fuel-taxes-road-funding-traffic-relief/", category: "Funding")
let newPost10 = Post(id: 6485, title: "Highway Funding", date: "2016-12-01T11:01:24", url: "http://www.wsj.com/articles/numbers-dont-add-up-for-trumps-trillion-dollar-building-plan-1480538796", category: "Funding")
posts.removeAll()
print("Num Posts: (self.numPosts)")
if numPosts >= 0 { posts.append(newPost) }
if numPosts >= 1 { posts.append(newPost2) }
if numPosts >= 2 { posts.append(newPost3) }
if numPosts >= 3 { posts.append(newPost4) }
if numPosts >= 4 { posts.append(newPost5) }
if numPosts >= 5 { posts.append(newPost6) }
if numPosts >= 6 { posts.append(newPost7) }
if numPosts >= 7 { posts.append(newPost8) }
if numPosts >= 8 { posts.append(newPost9) }
if numPosts >= 9 { posts.append(newPost10) }
print("Posts Count: (posts.count)")
self.tableView.reloadData()
tableView.reloadData()
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
// MARK: - Table view data source
//Count Number of Sections
override func numberOfSections(in tableView: UITableView) -> Int {
// #warning Incomplete implementation, return the number of sections
return 1
}
//Count Number of Rows in Section
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
// #warning Incomplete implementation, return the number of rows
print(posts.count)
return posts.count
}
//Populate Rows with Content
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
//DELETE let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath)
let cell:CustomTableCell = self.tableView.dequeueReusableCell(withIdentifier: "Cell") as! CustomTableCell
cell.titleLabel?.text = posts[indexPath.item].title
//Format Date String, Set Cell's Date Text
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss"
let stringDate = dateFormatter.string(from:posts[indexPath.item].date)
let dateYear = "(stringDate[stringDate.index(stringDate.startIndex, offsetBy:0)])(stringDate[stringDate.index(stringDate.startIndex, offsetBy:1)])(stringDate[stringDate.index(stringDate.startIndex, offsetBy:2)])(stringDate[stringDate.index(stringDate.startIndex, offsetBy:3)])"
let dateMonthNumber = Int("(stringDate[stringDate.index(stringDate.startIndex, offsetBy:5)])(stringDate[stringDate.index(stringDate.startIndex, offsetBy:6)])")
var dateMonth = ""
if dateMonthNumber == 01 { dateMonth = "January" }
else if dateMonthNumber == 02 {dateMonth = "February" }
else if dateMonthNumber == 03 {dateMonth = "March" }
else if dateMonthNumber == 04 {dateMonth = "April" }
else if dateMonthNumber == 05 {dateMonth = "May" }
else if dateMonthNumber == 06 {dateMonth = "June" }
else if dateMonthNumber == 07 {dateMonth = "July" }
else if dateMonthNumber == 08 {dateMonth = "August" }
else if dateMonthNumber == 09 {dateMonth = "September" }
else if dateMonthNumber == 10 {dateMonth = "October" }
else if dateMonthNumber == 11 {dateMonth = "November" }
else if dateMonthNumber == 12 {dateMonth = "December" }
var dateDay = "(stringDate[stringDate.index(stringDate.startIndex, offsetBy:8)])(stringDate[stringDate.index(stringDate.startIndex, offsetBy:9)])"
//Remove 0 from beginning of first 9 days of month (01 becomes 1, 02 becomes 2, etc.)
if dateDay.hasPrefix("0") { dateDay = "(stringDate[stringDate.index(stringDate.startIndex, offsetBy:9)])" }
//DELETE cell.detailTextLabel?.text = dateMonth + " " + String(dateDay) + ", " + String(dateYear)
cell.dateLabel?.text = "Date: " + dateMonth + " " + String(dateDay) + ", " + String(dateYear)
//Populate Category
cell.categoryLabel?.text = "Category: " + posts[indexPath.item].category

print("cell called")
return cell
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
//Checks that Web View Segue was Activated
if segue.identifier == "webViewSegue" {
// Make sure segue destination can be a Web View Controller
if let destination = segue.destination as? WebViewController {
//Get the Index Path for Clicked Cell (so we know which URL in array to grab), set URL in destination WebViewController
let indexPath = self.tableView.indexPathForSelectedRow!.row
destination.urlAddress = posts[indexPath].url
}
}
if segue.identifier == "filterSegue" {
print("FILTER ACTIVATED")
}
}
}

过滤器视图控制器：

import UIKit
class FilterViewController: UIViewController {
@IBAction func cancelAction(_ sender: UIBarButtonItem) {
_ = navigationController?.popViewController(animated: true)
dismiss(animated: true, completion:nil)
}
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
var titleView: UIImageView
titleView = UIImageView(frame:CGRect(x: 0, y: 0, width: 50, height: 60))
titleView.contentMode = .scaleAspectFit
titleView.image = UIImage(named: "860logo.png")
self.navigationItem.titleView = titleView
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
//Checks that Web View Segue was Activated
if segue.identifier == "setFilterSegue" {
// Make sure segue destination can be a Web View Controller
if let destination = segue.destination as? TableViewController {
//Get the Index Path for Clicked Cell (so we know which URL in array to grab), set URL in destination WebViewController
destination.numPosts = 3
destination.tableView.reloadData()
_ = navigationController?.popViewController(animated: true)
dismiss(animated: true, completion:nil)
}
}
}
}

Answer 1

viewDidLoad仅在最初加载视图(例如从情节提要)时调用一次

如果希望每次显示视图时都发生一些事情，请使用viewWillAppear或viewDidPear。

以下两行代码执行相同的操作：

self.tableView.reloadData()
tableView.reloadData()

注意：tableView.reloadData必须在主线程上调用。您可能需要按照以下方式包装调用以重新加载数据：

// for Swift 3
DispatchQueue.main.async {
self.tableView.reloadData()
}

Answer 2

• 首先这两行是冗余的：

  self.tableView.reloadData()
  tableView.reloadData()
  

  删除第一个。

• 其次，移动行以将表视图重新加载到viewWillAppear中。与仅调用一次的viewDidLoad不同，每当要显示视图时，都会多次调用viewWillAppear。

  override func viewWillAppear(_ animated: Bool) {
  super.viewWillAppear(animated)
  tableView.reloadData()
  }
  

最后，创建日期字符串的方法真的很可怕。还有一种更方便的方法。

更换

//Format Date String, Set Cell's Date Text
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss"
let stringDate = dateFormatter.string(from:posts[indexPath.item].date)
let dateYear = "(stringDate[stringDate.index(stringDate.startIndex, offsetBy:0)])(stringDate[stringDate.index(stringDate.startIndex, offsetBy:1)])(stringDate[stringDate.index(stringDate.startIndex, offsetBy:2)])(stringDate[stringDate.index(stringDate.startIndex, offsetBy:3)])"
let dateMonthNumber = Int("(stringDate[stringDate.index(stringDate.startIndex, offsetBy:5)])(stringDate[stringDate.index(stringDate.startIndex, offsetBy:6)])")
var dateMonth = ""
if dateMonthNumber == 01 { dateMonth = "January" }
else if dateMonthNumber == 02 {dateMonth = "February" }
else if dateMonthNumber == 03 {dateMonth = "March" }
else if dateMonthNumber == 04 {dateMonth = "April" }
else if dateMonthNumber == 05 {dateMonth = "May" }
else if dateMonthNumber == 06 {dateMonth = "June" }
else if dateMonthNumber == 07 {dateMonth = "July" }
else if dateMonthNumber == 08 {dateMonth = "August" }
else if dateMonthNumber == 09 {dateMonth = "September" }
else if dateMonthNumber == 10 {dateMonth = "October" }
else if dateMonthNumber == 11 {dateMonth = "November" }
else if dateMonthNumber == 12 {dateMonth = "December" }
var dateDay = "(stringDate[stringDate.index(stringDate.startIndex, offsetBy:8)])(stringDate[stringDate.index(stringDate.startIndex, offsetBy:9)])"
//Remove 0 from beginning of first 9 days of month (01 becomes 1, 02 becomes 2, etc.)
if dateDay.hasPrefix("0") { dateDay = "(stringDate[stringDate.index(stringDate.startIndex, offsetBy:9)])" }
//DELETE cell.detailTextLabel?.text = dateMonth + " " + String(dateDay) + ", " + String(dateYear)
cell.dateLabel?.text = "Date: " + dateMonth + " " + String(dateDay) + ", " + String(dateYear)

带有

//Format Date String, Set Cell's Date Text
let dateFormatter = DateFormatter()
dateFormatter.locale = Locale(identifier: "en_US_POSIX")
dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss"
let date = dateFormatter.date(from: posts[indexPath.item].date)!
dateFormatter.dateFormat = "MMMM d, yyyy"
cell.dateLabel?.text = "Date: " + dateFormatter.string(from:date)

Answer 3

您必须手动调用tableView.reloadData()。目前您只在viewDidLoad()中调用它，这意味着只有在加载视图时才会调用它。

另一个想法是，如果您正在修改另一个视图中的数据(并且该视图尚未卸载)，则在viewDidAppear()中调用它。