如何顯示在AutoID子項下保存的Firebase中的數據？

Question

我正在創建一個清單應用程序，以便跟蹤實驗室中保存的物品。 在實驗室中，有不同的工作站，其中包含不同的項目，如您所見，這些工作站在Firebase數據庫中的結構正確。

Firebase數據庫

iPhone模擬器

當我嘗試從tableCell中刪除特定項目時，出現了我的問題。 我可以將其從用戶界面中刪除，但在Firebase中，數據仍然保留。 我已經進行了無限制的研究，但是找不到與該特定問題有關的任何內容。

數據服務類

let DB_BASE = FIRDatabase.database().reference().child("laboratory")       //contains the root of our database
let STORAGE_BASE = FIRStorage.storage().reference()

class DataService {

static let ds = DataService()

//DB References
private var _REF_BASE = DB_BASE
private var _REF_STATION = DB_BASE.child("stations")
private var _REF_USERS = DB_BASE.child("users")

//Storage Reference
private var _REF_ITEM_IMAGE = STORAGE_BASE.child("item-pics")

var REF_BASE: FIRDatabaseReference {
    return _REF_BASE
}

var REF_STATION: FIRDatabaseReference {
    return _REF_STATION
}

var REF_USERS: FIRDatabaseReference {
    return _REF_USERS
}

var REF_ITEM_IMAGES: FIRStorageReference {
    return _REF_ITEM_IMAGE
}

//creating a new user into the firebase database

func createFirebaseDBUser(_ uid: String, userData: Dictionary<String, String>) {
    REF_USERS.child(uid).updateChildValues(userData)
}
}

庫存視圖控制器

import UIKit
import Firebase

class InventoryViewController: UIViewController, UITableViewDataSource,    UITableViewDelegate, UIImagePickerControllerDelegate,   UINavigationControllerDelegate {

var items = [Item]()

private var _station: Station!
private var _item: Item!

var sortIndex = 3

var imagePicker: UIImagePickerController!
static var imageCache: NSCache<NSString, UIImage> = NSCache()
var imageSelected = false

@IBOutlet weak var itemImageToAdd: UIImageView!
@IBOutlet weak var objectTextInput: UITextField!
@IBOutlet weak var brandTextInput: UITextField!
@IBOutlet weak var unitTextInput: UITextField!
@IBOutlet weak var amountTextInput: UITextField!
@IBOutlet weak var tableView: UITableView!
@IBOutlet var addItemView: UIView!
@IBOutlet weak var currentStationLabel: UILabel!

var station: Station {
    get {
        return _station
    } set {
        _station = newValue
    }
}

override func viewDidLoad() {
    super.viewDidLoad()

    var currentStationName = station.title

    currentStationLabel.text = currentStationName

    self.items = []

    let currentStation = station.title
    let stationRef = DataService.ds.REF_STATION.child(currentStation!)
    let inventoryRef = stationRef.child("inventory")

    tableView.delegate = self
    tableView.dataSource = self

    imagePicker = UIImagePickerController()
    imagePicker.allowsEditing = true
    imagePicker.delegate = self

    inventoryRef.observe(.value, with: { (snapshot) in
        print(snapshot.value!)

        self.items = []

        if let snapshot = snapshot.children.allObjects as? [FIRDataSnapshot] {

            for snap in snapshot {

                print("SNAP: \(snap)")
                if let itemDict = snap.value as? Dictionary<String, AnyObject> {

                    let key = snap.key
                    let item = Item(itemKey: key,
                                    itemData: itemDict)
                    self.items.append(item)
                }
            }
        }
        self.tableView.reloadData()
    })


}

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let item = items[indexPath.row]

    if let cell = tableView.dequeueReusableCell(withIdentifier: "inventoryTableCell", for: indexPath) as? ItemCell {

        if let img = InventoryViewController.imageCache.object(forKey: NSString(string: item.imageURL!)) {

            cell.updateItemUI(item: item, img: img)

        } else {

            cell.updateItemUI(item: item)
        }

        return cell

    } else {

        return ItemCell()
    }
}
func numberOfSections(in tableView: UITableView) -> Int {
    return 1
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return items.count
}

func postToFirebase(itemImageURL: String) {

    let post: Dictionary<String, AnyObject> = [
        "objectLabel": objectTextInput.text! as AnyObject,
        "brandLabel": brandTextInput.text! as AnyObject,
        "unitLabel": unitTextInput.text! as AnyObject,
        "amountLabel": amountTextInput.text! as AnyObject,

        //post elsewhere as an image for future reference
        "itemImageURL": itemImageURL as AnyObject,

        ]
    let stationText = _station.title
    let stationRef = DataService.ds.REF_STATION.child(stationText!)
    let inventoryRef = stationRef.child("inventory")

    let firebasePost = inventoryRef.childByAutoId()
    firebasePost.setValue(post)

    objectTextInput.text = ""
    brandTextInput.text = ""
    unitTextInput.text = ""
    amountTextInput.text = ""
    imageSelected = false

    tableView.reloadData()
}

func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : Any]) {
    if let image = info[UIImagePickerControllerEditedImage] as? UIImage {

        itemImageToAdd.image = image
        imageSelected = true
    } else {

        print("Please select a valid image")
    }

    imagePicker.dismiss(animated: true, completion: nil)
}

@IBAction func backToStations(_ sender: Any) {

    performSegue(withIdentifier: "backToStations", sender: nil)

}

func tableView(_ tableView: UITableView, canEditRowAt indexPath: IndexPath) -> Bool {
    return true
}

func tableView(tableView: (UITableView!), commitEditingStyle editingStyle: UITableViewCellEditingStyle, forRowAtIndexPath indexPath: (NSIndexPath!)) {

}

func tableView(_ tableView: UITableView, editActionsForRowAt indexPath: IndexPath) -> [UITableViewRowAction]? {

    let currentStation = station.title
    let stationRef = DataService.ds.REF_STATION.child(currentStation!)
    let inventoryRef = stationRef.child("inventory")

    var deleteAction = UITableViewRowAction(style: .default, title: "Delete") {action in

        //Insert code to delete values from Firebase
        self.items.remove(at: indexPath.row)
        tableView.deleteRows(at: [indexPath as IndexPath], with: .fade)

    }

    var editAction = UITableViewRowAction(style: .normal, title: "Edit") { action in

    }

    return [deleteAction, editAction]
}  
}

我的想法是在刪除后調用self_items.key，使其對應於特定tableCell行的當前鍵。 從那里，我將使用當前的按鍵，將是autoID並以這種方式刪除該值。 不幸的是，這使程序崩潰並出現致命的nil錯誤。

Answer 1

我發現解決此問題的最佳方法是在刪除操作中，從Firebase中刪除對象。 不要從此處更改tableview。

然后在數據偵聽器中，檢查數據何時以已刪除（或NULL）的形式返回，然后將其從tableview數據源數組中刪除並更新tableview。