Question

我遵循了1个教程，我能够使用一些数据（imageview和文本）填充collectionView：

let appleProducts = ["A", "B", "C", "D"]
let imageArray = [UIImage(named: "pug1"), UIImage(named: "pug2"), UIImage(named: "pug3"), UIImage(named: "pug4")]
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int
{

    return appleProducts.count
}

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell
{

    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath as IndexPath) as! CollectionViewCell

    cell.imageView?.image = self.imageArray[indexPath.row]

    cell.title?.text = self.appleProducts[indexPath.row]
    return cell

}

现在从演示项目传递到我的，我想用FirebaseDatabse中的数据（图片和文本）填充这个CollectionView，所以我创建了这个方法：

struct item {
let pictureId: String!
let picture: String!
}
var items = [item]()
   func getLatestAddedItems(){
    self.items.removeAll()
    let databaseRef = FIRDatabase.database().reference()
    databaseRef.child("Items").observe(.value, with: {
        snapshot in

        //self.items.insert(item(picture: picture), at: 0)
        for childSnap in snapshot.children.allObjects {

            let snap = childSnap as! FIRDataSnapshot
            //print(snap.key)

            let picture = (snap.value as? NSDictionary)?["bookImage"] as? String ?? ""
            //print(picture)
            self.items.append(item(pictureId:snap.key, picture:picture))

        }
        print(self.items.count)


    })
}

我创建此按钮以调用GetLatestAddedItems方法：

@IBAction func selectAction(_ sender: AnyObject) {
    getLatestAddedItems()
        }

这一个检查结果：

@IBAction func gettableAction(_ sender: AnyObject) {

    print(self.items[0].picture)
    print(self.items[1].picture)
    print(self.items[2].picture)
    print(self.items.count)    }

OutPut结果：

picture 1 link
picture 2 link
picture 3 link
3

现在，在ContentView方法中进行必要的更改之后，Everythings看起来很好并且正确无误：

func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int
{

    return items.count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell
{

    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath as IndexPath) as! CollectionViewCell

    //cell.imageView?.image = self.imageArray[indexPath.row]
     let url = NSURL(string: items[indexPath.row].picture)
     let data = NSData(contentsOf: url! as URL)
     cell.imageView?.image = UIImage(data: data! as Data)

    cell.title?.text = self.items[indexPath.row].pictureId
    return cell

}

现在我得到一个空的ContentView，第一次使用按钮它是有效的，因为我调用getLatestAddedItems（）将获取并向Items表添加数据，我尝试在ViewWillAppear或Viewdidload中调用它但是没有更改

这就是我认为return items.count返回0所以nothings会出现任何建议吗？

Answer 1

将您的collectionView的协议委派初始化移至 ViewController生命周期范围之一，例如 viewDidLoad() 或< strong> viewWillAppear(_animated : Bool) 如果您正在使用自定义viewController（即在viewController中嵌入collectionView）

每次用户从数据库中收到值时重新加载collectionView。

override func viewDidLoad(){
  super.viewDidLoad()

  self.collectionView.dataSource = self 
  self.collectionView.delegate = self 

 }

func getLatestAddedItems(){
 self.items.removeAll()
 let databaseRef = FIRDatabase.database().reference()
 databaseRef.child("Items").observe(.childAdded, with: {
    snapshot in

    for childSnap in snapshot.children.allObjects {

        let snap = childSnap as! FIRDataSnapshot
        let picture = (snap.value as? NSDictionary)?["bookImage"] as? String ?? ""
         self.items.append(item(pictureId:snap.key, picture:picture))
         print(self.items.count)
         self.collectionView.reloadData() 
     }
   })
}

PS： - 对firebase服务器的所有调用都是异步的，这需要一些时间从FBDB中检索数据，因此请print(self.items.count)在firebase观察调用的 completionBlock 内部，否则如果它被放在外面，它甚至会在从FBDB检索到数据之前被调用。

空集合视图斯威夫特

1 个答案: