ios - 如何实现prepareForReuse()来防止褪色的单元格表现得很奇怪？

Question

我使用 self.like.alpha = 0.5 来突出显示 .被喜欢的用户旁边的“喜欢”按钮。滚动会导致突出显示有时消失并出现在其他用户旁边。

我发现我可以使用 A)prepareForReuse 或 B)执行类似伪代码的操作(尽管 IsLiked 必须以某种方式限制在该 session 中):

cell.like.alpha = item.isLiked ? 0.5 : 1

这是我的代码:

在 View ControllerTableViewCell.swift中:

 @IBAction func likePressed(_ sender: Any) {

 self.like.alpha = 0.5
   let ref = Database.database().reference()
let keyToPost = ref.child("likes").childByAutoId().key

ref.child("humans").child(self.postID).observeSingleEvent(of: .value, with:  {(snapshot) in

    if let humans = snapshot.value as? [String: AnyObject] {
        let updateLikes: [String: Any] = ["humansWhoLike/\(keyToPost)" : Auth.auth().currentUser!.uid]

        ref.child("humans").child(self.postID).updateChildValues(updateLikes, withCompletionBlock: { (error, reff) in

            if error == nil {
                ref.child("humans").child(self.postID).observeSingleEvent(of: .value, with: { (snap) in
                    if let properties = snap.value as?[String: AnyObject]{
                        if let likes = properties["humansWhoLike"] as? [String : AnyObject] {
                            let count = likes.count
                        let update = ["likes" : count]
                            ref.child("humans").child(self.postID).updateChildValues(update)

                        }
                    }
                })
            }
        })
    }
})
ref.removeAllObservers()
 }

在 homepage.swift 中(使用 like 按钮的地方):

public override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath) as! ViewControllerTableViewCell

let like = cell.viewWithTag(3) as! UIButton


let immy = cell.viewWithTag(1) as! UIImageView

let person: Userx = humans[indexPath.row]

cell.lblName.text = person.Education

cell.postID = self.humans[indexPath.row].postID

if let PhotoPosts = person.PhotoPosts {
    let url = URL(string: PhotoPosts)
    immy.sd_setImage(with: url)
}
return cell
}

当单元格在滚动后被重用时，我需要像淡入淡出这样的功能，以便不会消失，也不会转到其他用户那里。

数据库结构:

 "humans" : {
"5VbL3Adj7teM2KNJkF4GIexBJhE2" : {
  "Coordinates" : {
    "latitude" : 42.8864,
    "longitude" : 78.8784
  },
  "Education" : "Yale Accounting",
  "PhotoPosts" : "https://firebasestorage.googleapis.com/v0/b/daylike-2f938.appspot.com/o/images%2FPhotoPosts?alt=media&token=42d76567-ac42-4728-9914-1d7c2fa4d5e6",
  "WhatIamConsideringBuying" : "Twitter: Carla9",
  "caption" : 1565896677651,
  "caption1" : {
    "caption1" : 1566734644170,
    "keyToPost" : "-Ln7eM9S_pSQ_aqRPz0k"
  },
  "likes" : 82,
  "peopleWhoLike" : {
    "-LmLjHwwGj1kt5qLM20X" : "NMNQYJ5z64fATK2MMs7m0ggHl0k2",
    "-LmLtlp5Sm900SV8xP4i" : "NMNQYJ5z64fATK2MMs7m0ggHl0k2",
    "-LmLuOzQ0TZ9uJ_uNkkg" : "NMNQYJ5z64fATK2MMs7m0ggHl0k2",
    "-LmLultcrrsG2NjEYoTe" : "NMNQYJ5z64fATK2MMs7m0ggHl0k2",
    "-LmLvMseSmFhnxEGGctU" : "NMNQYJ5z64fATK2MMs7m0ggHl0k2",
    "-LmLvVQokDCZLFrnhaLu" : "NMNQYJ5z64fATK2MMs7m0ggHl0k2",

  },
  "postID" : "5VbL3Adj7teM2KNJkF4GIexBJhE2",
  "users" : "carla19martin@me.com"
},
"9RYUttVhCzXKs6H1XnZ63TZ8Dun2" : {

Answer 1

您需要在cellForRow方法中设置每个单元格的alpha。您不应根据单元格本身向您的 likePressed() 方法发送操作来更改它。相反，它应该反射(reflect)您的底层数据模型，我假设您已在本地缓存。

public override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath) as! ViewControllerTableViewCell
    let like = cell.viewWithTag(3) as! UIButton
    let immy = cell.viewWithTag(1) as! UIImageView
    let person: Userx = humans[indexPath.row]
    cell.lblName.text = person.Education
    cell.postID = self.humans[indexPath.row].postID

    if let PhotoPosts = person.PhotoPosts {
        let url = URL(string: PhotoPosts)
        immy.sd_setImage(with: url)
    }

    // You need to set the alpha here in cellForRow method
    // Your idea using nil coalescing is good, as it must always be set afresh for the relevant cell (so it is correct when reused)
    // Get value of isLiked - this depends on your database and local cache
    // This is an example - accessing the isLiked property may be different depending on your data model

    cell.like.alpha = posts[indexPath.row].isLiked ? 0.5 : 1

    return cell
}