Question

在Swift 3中，我尝试创建一个“过滤器”视图，该视图允许用户按类别和按日期过滤表格视图中的帖子。目前，过滤视图以模态方式显示，并在您单击“完成”时被取消。

我还没有设置日期/类别功能。首先，我只是尝试将 tableView 更新为仅显示3个帖子而不是10。为此，我在destination.numPosts = 3中设置了FilterViewController。

使用print语句，可以看出TableViewController确实更新了viewDidLoad函数中的posts数组，以便发布3个帖子。 numberOfRowsInSection被调用并且是正确的。 numberofSections始终返回1。在viewDidLoad中，我尝试了self.tableView.reloadData()和tableView.reloadData()但是，cellForRowAt indexPath仅在您最初运行应用时被调用，而当数据重新加载时它不会调用此方法

关于FilterViewController被解雇后如何重新填写帖子表的任何想法？

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

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。

如果要修改另一个视图中的数据（并且尚未卸载视图），另一个想法是在viewDidAppear（）中调用它。

Answer 2

viewDidLoad仅在最初加载视图时被调用一次（例如，从故事板中）

如果您希望每次显示视图时都要发生某些事情，请使用viewWillAppear或viewDidAppear。

以下两行代码执行相同的操作：

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

注意：必须在主线程上调用tableView.reloadData。您可能必须按如下方式将调用包装到reloadData：

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

Answer 3

首先，这两行是多余的：

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

删除第一个。

然后移动该行以将表格视图重新加载到viewWillAppear。与viewDidLoad不同，viewWillAppear仅在调用视图时多次调用override func viewWillAppear(_ animated: Bool) { super.viewWillAppear(animated) tableView.reloadData() }时调用。

//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)

最后你创建日期字符串的方式非常可怕。有一种更方便的方式。

替换

//Format Date String, Set Cell's Date Text
let dateFormatter = DateFormatter()
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)

与

RelativeLayout relativeLayout=(RelativeLayout) findViewById(R.id.relativeLayout);
RelativeLayout.LayoutParams relativeParams = new RelativeLayout.LayoutParams
 (RelativeLayout.LayoutParams.MATCH_PARENT, RelativeLayout.LayoutParams.WRAP_CONTENT);
  if(textVar != null)
  {
    relativeParams.addRule(RelativeLayout.BELOW, textVar.getId());
  } else {
    relativeParams.addRule(RelativeLayout.BELOW, R.id.text);
  }

  textVar=new EditText(MainActivity.this);
  textVar.setId(id++);
  textVar.setText("NEW");


 relativeLayout.addView(textVar, relativeParams);

cellForRowAt不使用reloadData（）方法调用indexPath

3 个答案: