ios - Swift Firebase 加载图片的次数太多

Question

我正在尝试从 Firebase 加载用户“帖子”(图片及其描述)。一开始一切似乎都运行良好，我在 viewController 中看到 3 个帖子，但是当我将新图像上传到 Firebase 时，用户发布的所有帖子的数量成倍增加，然后应用程序加载的不是 4 个帖子，而是 8 个帖子。为什么会这样？

这是我的截图

Snap (qUJAq6aeNGYUeSsl9RmzldNpTME3) {
"508D22DE-E865-460E-A011-A9170E0AB6A8" =     {
    description = n;
    downloadURL = "https://firebasestorage.googleapis.com/v0/b/findit-2f6eb.appspot.com/o/images%2F1A18AFAD-815C-417C-8C7A-226343FD0256.jpg?alt=media&token=46a6c929-a5ec-49e4-b6ca-aca896618fe0";
};
"D8434D58-1193-421D-8DFE-982983CB20D4" =     {
    description = Maaa;
    downloadURL = "https://firebasestorage.googleapis.com/v0/b/findit-2f6eb.appspot.com/o/images%2F059C91E8-95A8-44C6-9779-F678E2B9E033.jpg?alt=media&token=46ff5654-abec-49dc-bbb8-afae0eb6f1bd";
};
"F0E47F44-AE22-4D80-B173-E2168CB20B94" =     {
    description = 7;
    downloadURL = "https://firebasestorage.googleapis.com/v0/b/findit-2f6eb.appspot.com/o/images%2F1EA82DCA-FFE2-4B79-931C-28B66C7729AB.jpg?alt=media&token=8eaa2e02-5af8-4b43-adf2-2ac9214f902e";
};
}

MyPostsTableViewController

import UIKit

 import Firebase



  class MyPostsTableViewController: UITableViewController {
let user = Userr()
var downloadURL = ""



var desCription = ""
var allPosts = [String]()
let currUser = Auth.auth().currentUser?.uid

override func viewDidLoad() {
    super.viewDidLoad()



    let ref =  Database.database().reference().child("posts").child(currUser!)
    ref.observe(.value, with: { (snapshot) in

        print(snapshot)

        let dictionary = snapshot.value as! [String: Any]
        var keys = Array(dictionary.keys)
        self.allPosts = keys

        for index in 0...(keys.count - 1) {
            self.allPosts.removeAll()
            self.user.descriptions.removeAll()
            self.user.downloadUrls.removeAll()
        ref.child(keys[index]).child("description").observe( .value, with: { (snapshot) in
            ref.child(keys[index]).child("downloadURL").observe(.value, with: { (snapshot2) in
                self.user.descriptions.append(snapshot.value as! String)
                self.user.downloadUrls.append(snapshot2.value as! String)

                self.tableView.reloadData()

            })
        })


        }

    })


}




override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    // #warning Incomplete implementation, return the number of rows



        return user.descriptions.count

}


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



  //  print("downloadUrls Count \(user.downloadUrls.count)")


    cell.descriptionLabel.text = user.descriptions[indexPath.row]

   let profileImageURL = user.downloadUrls[indexPath.row]

    cell.imageVieeew.contentMode = .scaleAspectFit

    cell.imageVieeew.loadImageUsingCacheWithUrlString(profileImageURL)



    return cell

}



}

后 View Controller

  import UIKit
  import Firebase


class PostViewController: UIViewController, UIImagePickerControllerDelegate, UINavigationControllerDelegate {

let user = Userr()

@IBOutlet var textField: UITextField!
@IBAction func postToServer(_ sender: Any) {

       self.user.allow = false
    // successfully authenticated user
    if imageViw.image != nil && textField.text != ""{

        let imageName = NSUUID().uuidString
        let postName = NSUUID().uuidString
        let imagesFolder = Storage.storage().reference().child("images")

        if let imageData = UIImageJPEGRepresentation(imageViw.image!, 0.2){
            imagesFolder.child("\(imageName).jpg").putData(imageData, metadata: nil, completion:{
                (metadata, error) in

                if let error = error{
                    self.presentAlert(alert: error.localizedDescription)
                } else{
                    if let downloadURL =  metadata?.downloadURL()?.absoluteString {

                        let currUser = Auth.auth().currentUser?.uid
                         let ref = Database.database().reference().child("posts").child(currUser!).child(postName)
                        ref.child("downloadURL").setValue(downloadURL)
                        ref.child("description").setValue(self.textField.text!)

                    }
                }

            })


            }

    }
    else {
        // we're missing something
        presentAlert(alert: "You mus provide an image and a message for your post.")
    }


} 

Answer 1

每次添加新帖子时，代码都会附加另一个执行的监听器，因此您将为附加的每个监听器附加一次描述和 downloadUrls。没有必要单独监听每个 child ，因为对它们的任何更改都将由原始 .observe 监听器触发，因为路径的 .value 已更改。相反，遍历 childSnapshots 并根据需要附加数据。它看起来像这样，虽然我没有用你的数据和代码测试它，所以你可能需要调整它。

   let ref =  Database.database().reference().child("posts").child(currUser!)
   ref.observe(.value, with: { (snapshot) in

        print(snapshot)
        self.allPosts.removeAll()
        self.user.descriptions.removeAll()
        self.user.downloadUrls.removeAll()

        guard let snapshots = snapshot.children.allObjects as? [DataSnapshot] else { return }
        for snap in snapshots {
            self.user.descriptions.append(snap.childSnapshot(forPath: "description").value as! String)
            self.user.downloadUrls.append(snap.childSnapshot(forPath: "downloadURL").value as! String)
        }

        self.tableView.reloadData()
    })