Question

这里我首先从firebase中检索图像，然后将其添加到locationImage数组中，稍后将其添加到collectionView。

import UIKit
import Firebase
import FirebaseStorage

class ViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate {

var locationImage = [UIImage(named: "hawai"), UIImage(named: "mountain")]

override func viewDidLoad() {
    super.viewDidLoad()

    retrieveData()
}


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

    print(locationImage.count)
    return locationImage.count
}
func retrieveData(){
    let database = FIRDatabase.database().reference()
    let storage = FIRStorage.storage().reference()

    let imageRef = storage.child("blue blurr.png")

    imageRef.data(withMaxSize: (1*1000*1000)) { (data, error) in
        if error == nil{

            let tempImage = UIImage(data: data!)
            self.locationImage.append(tempImage)
            print("HELLLLLOOOO WOOOOORRRLLLDDDD")
            print(self.locationImage.count)
        }
        else{
            print(error?.localizedDescription)
        }
    }
    return
}

}

这里的retrieveData（）函数在collectionView（）之前调用。应首先调用viewdidload，我该怎么办呢，有人可以帮忙吗？

Answer 1

您不希望在ViewDidLoad之前调用collectionView吗？

override func viewDidLoad() {
    super.viewDidLoad()

    collectionView.dataSource = self
    collectionView.delegate = self
}

但是这不应该让你担心，因为如果你用来初始化CollectionView的数组是空的，那么如果调用转到numberOfItemsInSection方法就不重要了。

这里需要的是在locationImage中有数据后调用重新加载。所以在你的self.locationImage.append（tempImage）之后，添加：

self.collectionView.reloadData()

Answer 2

注释中的代码和数据源在代码中的建议并没有解决问题。

委托和数据源是在Interface Builder中连接还是在代码中连接是无关紧要的。显然它们是连接的，否则numberOfItemsInSection根本就不会被调用。

由于默认情况下数据源数组不为空numberOfItemsInSection在加载视图后隐式调用。那么你怎么知道什么时候调用viewDidLoad()而不打印消息？

在retrieveData中，数据库请求以异步执行，因此您需要在检索数据后重新加载集合视图

func retrieveData(){
    let database = FIRDatabase.database().reference()
    let storage = FIRStorage.storage().reference()

    let imageRef = storage.child("blue blurr.png")

    imageRef.data(withMaxSize: (1*1000*1000)) { (data, error) in
        if error == nil{

            let tempImage = UIImage(data: data!)
            self.locationImage.append(tempImage)
            self.collectionView.reloadData() // This line is crucial
            print("HELLLLLOOOO WOOOOORRRLLLDDDD")
        }
        else{
            print(error?.localizedDescription)
        }
    }
}

Answer 3

import UIKit
import Firebase
import FirebaseStorage

class ViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate {

var locationImage = [UIImage(named: "hawai"), UIImage(named: "mountain")]

override func viewDidLoad() {
    super.viewDidLoad()

    retrieveData()

    //Add these two line here remove delegate and datasource from storyborad
    collectionView.dataSource = self
    collectionView.delegate = self
}


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

    print(locationImage.count)
    return locationImage.count
}
func retrieveData(){
    let database = FIRDatabase.database().reference()
    let storage = FIRStorage.storage().reference()

    let imageRef = storage.child("blue blurr.png")

    imageRef.data(withMaxSize: (1*1000*1000)) { (data, error) in
        if error == nil{

            let tempImage = UIImage(data: data!)
            self.locationImage.append(tempImage)
            print("HELLLLLOOOO WOOOOORRRLLLDDDD")
            print(self.locationImage.count)
        }
        else{
            print(error?.localizedDescription)
        }
    }
    return
}

}

Answer 4

100％正常工作

您的UICollectionView的IBOutlet在哪里？

 @IBOutlet weak var collectionView: UICollectionView!

首先设置IBOutlet＆amp;试试这段代码：

import UIKit
import Firebase
import FirebaseStorage

 class ViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate {

var locationImage = [UIImage(named: "hawai"), UIImage(named: "mountain")]

override func viewDidLoad() {
super.viewDidLoad()
 //Add these two line here remove delegate and datasource from storyborad
collectionView.dataSource = self
collectionView.delegate = self
retrieveData()
}


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

print(locationImage.count)
return locationImage.count
 }
 func retrieveData(){
let database = FIRDatabase.database().reference()
let storage = FIRStorage.storage().reference()

let imageRef = storage.child("blue blurr.png")

imageRef.data(withMaxSize: (1*1000*1000)) { (data, error) in
    if error == nil{

        let tempImage = UIImage(data: data!)
        self.locationImage.append(tempImage)
        print("HELLLLLOOOO WOOOOORRRLLLDDDD")
        print(self.locationImage.count)
    }
    else{
        print(error?.localizedDescription)
    }
}
return
}

Answer 5

一个简单的解决方案是让您的函数休眠几秒钟，就像这样

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    do {
        sleep(1)
    }

编辑：格式化函数

在viewdidload（）之前调用numberOfItemsInSection函数

5 个答案: