UICollectionView 重新加载单元格但不删除旧单元格

Question

我一直在尝试实现一个集合视图，用户可以在其中点赞 post 但出于某种原因，当用户这样做时，它会更新提要，但只是将单元格数量加倍并留下应该消失的旧细胞。简而言之，一半的单元格被更新，另一半是旧值。基本上我无法弄清楚如何简单地更新当前单元格而不会出现问题。理想情况下，我希望用户按下“赞”按钮，除了该按钮转向 "Unlike" 并且 post 上的赞数在 collectionview 中发生更改外，不会发生其他任何事情。

这是加载集合视图单元格的代码：

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = feedCollectionView.dequeueReusableCell(withReuseIdentifier: cellIdentifier, for: indexPath) as! MyGroupFeedCollectionViewCell

    cell.postKey = feedArray[indexPath.row].postKey

    //clears the cells first
    cell.profileImage.image = nil
    cell.usernameLabel.text = nil
    cell.usernameLabel2.text = nil
    cell.groupName.text = nil
    cell.postImageView.image = nil
    cell.postCaptionTextView.text = nil
    cell.timeStamp.text = nil

    //load profile picture
    cell.profileImage.sd_setImage(with: URL(string: feedArray[indexPath.row].ProfilePic), placeholderImage: UIImage(named:"no profile picture.png"))

    //load username
    cell.usernameLabel.text = feedArray[indexPath.row].Username
    cell.usernameLabel2.text = feedArray[indexPath.row].Username

    //load groupName when in home feed
    cell.groupName.text = feedArray[indexPath.row].GroupName

    //load postImage
    cell.postImageView.sd_setImage(with: URL(string: feedArray[indexPath.row].PostImage), placeholderImage: UIImage(named:"penguinPanorama"))

    //load caption
    cell.postCaptionTextView.text = feedArray[indexPath.row].caption

    //load likes once likes are implemented
    //checks if the user has liked the post or not
    databaseRef.child("likes").child((FIRAuth.auth()?.currentUser?.uid)!).child(feedArray[indexPath.row].postKey).observe(.value, with: { (snapshot) in
        if(snapshot.exists())
        {
            cell.liked = "Yes"
            cell.likeButton.setTitle("Unlike", for: .normal)
        }
        else{
            cell.liked = "No"
            cell.likeButton.setTitle("Like", for: .normal)
        }
    })

下面是按下赞按钮的函数代码：

@IBAction func likeButton_tapped(_ sender: Any) {
    self.likeButton.isEnabled = false
    print(self.postKey)
    print(self.liked)

    //make it so liking or unliking adds or subtracts from the total number of likes on the post
    if liked == "Yes"
    {
         self.databaseRef.child("likes").child((FIRAuth.auth()?.currentUser?.uid)!).child(self.postKey).removeValue()

        let NewLikeNumber = likeNumber - 1
        self.databaseRef.child("GroupPosts").child(self.groupName.text!).child(self.postKey).child("likes").setValue(NewLikeNumber)
        print(NewLikeNumber)
    }
    else{
        self.databaseRef.child("likes").child((FIRAuth.auth()?.currentUser?.uid)!).child(self.postKey).setValue("")

        let NewLikeNumber = likeNumber + 1
        self.databaseRef.child("GroupPosts").child(self.groupName.text!).child(self.postKey).child("likes").setValue(NewLikeNumber)
        print(NewLikeNumber)
    }

    self.likeButton.isEnabled = true
}

Answer 1

对于点赞，我建议您使用 Firebase 交易，因为您的点赞计数可能会因为并发修改而变得一团糟：

 func likePost(_ post: Post, completion: @escaping () -> ()) {

    guard let currentUserId = Auth.auth().currentUser?.uid else {
       return
    }

    databaseRef.child(likes).child(currentUserId).child(postKey).runTransactionBlock ( { (currentData: MutableData) -> TransactionResult in

              if var data = currentData.value as? [String: Any] {
                  var count = data["likesCount"] as! Int
                  count += 1
                  data["likesCount"] = count
                  currentData.value = data
                  return TransactionResult.success(withValue: currentData)
              }

              return TransactionResult.success(withValue: currentData)

     }, andCompletionBlock: { (error, success, snapshot) in

                // ...

     })

}

当然，不喜欢 post 的用户也是如此。

现在要知道用户是否喜欢 post，您可以在 class 中创建一个布尔值以在本地保存喜欢的状态：

private var isPostLiked = false

每当用户点击“赞”按钮时，就做一个简单的检查：

     func handleLikeTapped() {

            guard let post = post else {
                return
            }

            if isPostLiked {

                NetworkManager.shared.likePost(post, completion: { [weak self] in

                    // Once the completion handler of your method is called, the likes count in your database is now updated. 
                    // To avoid making another read in the database just now, you can just
                    // Update your count (a label that shows how many likes a specific post received I guess ?) locally here so that the user can see in realtime the change (with animation or not depending on what you want to achieve)

                    // And finally update the like state of the post so that if the user click again on like it wouldn't mess everything up:

                    self?.isPostLiked = false
                })

            }

            else {

                NetworkManager.shared.dislikePost(post, completion: { [weak self] in

                    // ...
                })
            }
   }

当然，以后如果您需要在不同的视图控制器中访问点赞数，您只需使用 observeSingleEvent(of: .value) 从数据库中获取更新的点赞数。

如果您有任何问题，请告诉我！

UICollectionView 重新加载单元格但不删除旧单元格

UICollectionView Reloading cells but not deleting old ones

ios

uicollectionview

uicollectionviewcell

swift