Activity 指示器不会完成操作

Question

我有一个 activity 指示器，一旦从 Firebase 读取完成就会停止。

如果我有一个添加了产品的用户，指示器可以正常完成。唉，如果一个没有上传任何产品的用户试图查看他的产品，指示器将不会完成它的动作。

我的代码：

override func viewDidLoad()
{

    AddProductImage.image = #imageLiteral(resourceName: "PLUS")

    let singlePlusTap = UITapGestureRecognizer(target: self, action: Selector("AddProductTapDetected"))
    AddProductImage.isUserInteractionEnabled = true
    AddProductImage.addGestureRecognizer(singlePlusTap)
    // Do any additional setup after loading the view.
    self.MyProductsCollection.delegate = self
    self.MyProductsCollection.dataSource = self;


    // create a hover view that covers all screen with opacity 0.4 to show a waiting action
    let fadeView:UIView = UIView()
    fadeView.frame = self.view.frame
    fadeView.backgroundColor = UIColor.white
    fadeView.alpha = 0.4

    // add fade view to main view
    self.view.addSubview(fadeView)
    // add activity to main view
    self.view.addSubview(activityView)
    activityView.hidesWhenStopped = true
    activityView.center = self.view.center
    // start animating activity view
    activityView.startAnimating()

    self.ref = Database.database().reference()
    let loggedOnUserID = Auth.auth().currentUser?.uid


    if let currentUserID = loggedOnUserID
    {
        // Retrieve the products and listen for changes
         self.ref?.child("Users").child(currentUserID).child("Products").observe(.childAdded, with:
            { (snapshot) in

                // Code to execute when new product is added
                let prodValue = snapshot.value as? NSDictionary
                let prodName = prodValue?["Name"] as? String ?? ""
                let prodPrice = prodValue?["Price"] as? Double ?? -1
                let prodDesc = prodValue?["Description"] as? String ?? ""
                let prodURLS = prodValue?["MainImage"] as? String
                let prodAmount = prodValue?["Amount"] as? Int ?? 0
                let prodID = snapshot.key

                let prodToAddToView = Product(name: prodName, price: prodPrice, currency: "NIS", description: prodDesc, location: "IL",
                                              toSell: false, toBuy: false, owner: currentUserID, uniqueID: prodID, amount: prodAmount, mainImageURL: prodURLS)


                self.products.append(prodToAddToView)
                DispatchQueue.main.async
                    {
                        self.MyProductsCollection.reloadData()
                        // remove the hover view as now we have data
                        fadeView.removeFromSuperview()
                        // stop animating the activity
                        self.activityView.stopAnimating()
                }
        }
        ) // Closes observe function
    }
    super.viewDidLoad()

}

Answer 1

.childAdded 事件仅在出现 child 时触发。因此，正如您所指出的：如果可能没有 children，则不能使用 .childAdded 来隐藏 activity 指标。

唯一保证触发的事件是 .value，因此您需要使用它来检测条件：

let ref = self.ref?.child("Users").child(currentUserID).child("Products")
ref.observe(.value, with:
        { (snapshot) in
    self.activityView.stopAnimating()
})

如果您这样做，无论如何您都会在此处理程序中获得 child 节点。所以你也可以考虑遍历 snapshot 的 child 节点并在这里处理它们：

ref.observe(.value, with:
        { (snapshot) in
    self.activityView.stopAnimating()
    for child in snapshot.children.allObjects as [FIRDataSnapshot] {
       ...
    }
})

Activity 指示器不会完成操作

Activity indicator won't finish action

swift

firebase

firebase-realtime-database

uicollectionview

uiactivityindicatorview