调用函数为类成员设置标签

Posted 2023-02-24

【中文标题】调用函数为类成员设置标签

【英文标题】：Calling a Function to Set a Label for a Member of a Class

【发布时间】：2019-06-07 19:39:43

【问题描述】：

我在UITableView cells 中有一系列帖子。我做了一个功能，当你点击cell时，你会转到一个新的UIViewController。现在我希望新的UIViewController 根据您点击的帖子更新正文和标题。我有以下新 UIViewController 的文本：

import UIKit
import Firebase
class MainTextView: UIViewController 
    @IBOutlet weak var titleText: UILabel!
    @IBOutlet weak var mainText: UILabel!

    func setMain(post:Post)
        titleText.text = post.text
        mainText.text = post.title
    

我的主视图控制器的以下文本：

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) 
    tableView.deselectRow(at: indexPath as IndexPath, animated: true)
    let row = indexPath.row
    print("Row: \(row)")
    let destination = storyboard!.instantiateViewController(withIdentifier: "MainTextView") as! MainTextView
    navigationController?.pushViewController(destination, animated: true)
    destination.setMain(post: posts[indexPath.row])

这是我的帖子类：

导入基础

类帖子 变量 ID：字符串 变量标题：字符串 可变文本：字符串 var createdAt:Date

init(id: String, title: String,text:String,  timestamp:Double) 
    self.id = id
    self.title = title
    self.text = text
    self.createdAt = Date(timeIntervalSince1970: timestamp / 1000)

我应该注意，我的 HomeViewController 函数 fetchPost 中也出现以下错误：

 func fetchPosts(completion:@escaping (_ posts:[Post])->()) 
    let postsRef = Database.database().reference().child("posts")
    var queryRef:DatabaseQuery
    let lastPost = posts.last
    if lastPost != nil 
        let lastTimestamp = lastPost!.createdAt.timeIntervalSince1970 * 1000
        queryRef = postsRef.queryOrdered(byChild: "timestamp").queryEnding(atValue: lastTimestamp).queryLimited(toLast: 20)
     else 
        queryRef = postsRef.queryOrdered(byChild: "timestamp").queryLimited(toLast: 20)
    

    queryRef.observeSingleEvent(of: .value, with:  snapshot in
        var tempPosts = [Post]()

        for child in snapshot.children 
            if let childSnapshot = child as? DataSnapshot,
                let dict = childSnapshot.value as? [String:Any],
                let title = dict["text"] as? String,

                let text = dict["title"] as? String,
                let timestamp = dict["timestamp"] as? Double 

                if childSnapshot.key != lastPost?.id 
                    let post = Post(id: childSnapshot.key, title: title, text: text, timestamp:timestamp)
                    tempPosts.insert(post, at: 0)
                

            
        

        return completion(tempPosts)
    )

这是我的 fetchPosts 函数：

func fetchPosts(completion: @escaping( _ posts:[Post])->()) 

        let postsRef = Database.database().reference().child("posts")
        let lastPost = self.posts.last
        var queryRef:DatabaseQuery

        if lastPost == nil 
            queryRef = postsRef.queryOrdered(byChild: "timestamp").queryLimited(toLast: 10)
         else
           let lastTimestamp = lastPost!.createdAt.timeIntervalSince1970 * 1000
            queryRef = postsRef.queryOrdered(byChild: "timestamp").queryEnding(atValue: lastTimestamp)
        


        queryRef.observeSingleEvent(of: .value, with: snapshot in

            var tempPosts = [Post]()

            for child in snapshot.children 
                if let childSnapshot = child as? DataSnapshot,
                    let dict = childSnapshot.value as? [String:Any],
                    let text = dict["text"] as? String,
                    let comment = dict["comment"] as? Array<String>,
                    let title = dict["title"] as? String,
                    let timestamp = dict["timestamp"] as? Double
                    if childSnapshot.key != lastPost?.id 
                        let post = Post(id: childSnapshot.key, title: text, text: title, comment: comment, timestamp: timestamp)
                        tempPosts.insert(post, at: 0)
                    

                
            
            return completion(tempPosts)

        )



    

【问题讨论】：

destination.setMain(post: somePost).

我用destination.setMain(post:Post)替换了setMain(post:Post)。我收到错误：无法将类型“Post.Type”的值转换为预期的参数类型“Post”。我对你在这里的意思有点困惑。我也尝试了 somePost 并出现错误...谢谢您的帮助

我放了somePost，因为你需要传递Post对象的一些实例。

看来你是对的！我需要了解实例。这看起来是一个好的开始：***.com/questions/45989491/…

【参考方案1】：

更改 MainTextView 控制器的逻辑：

import UIKit
import Firebase

class MainTextView: UIViewController 

  // MARK: - Your properties

  @IBOutlet weak var titleText: UILabel!

  @IBOutlet weak var mainText: UILabel!

  var post: Post?

  // MARK: - View Controller LifeCycle

  override func viewWillAppear(_ animated: Bool) 
    super.viewWillAppear(animated)
    self.setMain()
  

  private func setMain() 
      guard let post = self.post else 
          return
      

      titleText.text = post.text
      mainText.text = post.title
  

你也应该改变控制器的逻辑

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) 
  tableView.deselectRow(at: indexPath as IndexPath, animated: true)

  if let destination = storyboard?.instantiateViewController(withIdentifier:"MainTextView") as? MainTextView 
      destination.post = <list of post>[indexPath.row]
      navigationController?.pushViewController(destination, animated: true)
  

如果你在你的项目中使用 segues，你可以试试这个决定：

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) 
  tableView.deselectRow(at: indexPath as IndexPath, animated: true)
  performSegue(withIdentifier: "Your segue name", sender: self)


override func prepare(for segue: UIStoryboardSegue, sender: Any?) 
    if segue.identifier == "Your segue name", let destination = segue.destination as? MainTextView 
        destination.post = <Your selected post>
    

【讨论】：

当你写 你到底是什么意思？我只想要与给定索引对应的点（用户生成）。在这里我会很感激。

这个成功了！非常感谢。仍然对您使用 segues 的替代解决方案感到好奇...另外，您建议如何为帖子制作 cmets？

【参考方案2】：

通过

destination.setMain(post: Post)

因为函数位于目标类而不是HomeViewController