Ios 从UITableView中滚动更改URL加载的图像

我目前正在从Firebase加载一个tableView。此内容包括一张图片，当用户滚动时，该图片将更改，直到最终图像稳定下来。我认为这将是在成功加载每个单元之前为每个单元分配一个图像，但无法找到解决方法

我必须填充tableView的当前代码如下：

表格视图

import UIKit
import FirebaseAuth
import FirebaseStorage

class Articles: UITableViewController {

var vcType:String = "Home"
var rooms = [Room]()
var articleCell = ArticlesCell()
@IBOutlet weak var menuButton: UIBarButtonItem!
override func viewDidLoad() {
    super.viewDidLoad()

    if self.vcType == "Home"
    {
        self.rooms += ArticlesManager.sharedClient.rooms
    }
    else
    {
        if let obj = ArticlesManager.sharedClient.catRooms[self.vcType.lowercased()] //as? [Room]
        {
            self.rooms += obj
        }
    }
    self.tableView.reloadData()

    ArticlesManager.sharedClient.blockValueChangeInRoomArray = {
        newRoom in
        if self.vcType == "Home"
        {
            self.rooms.append(newRoom)
            self.rooms.sort(by: {
                if $0.created_Date == nil
                {
                    return false
                }
                if $1.created_Date == nil
                {
                    return true
                }

                return $0.created_Date.compare($1.created_Date) == ComparisonResult.orderedDescending
            })

        }
        else
        {
            if self.vcType.lowercased() == newRoom.category
            {
                self.rooms.append(newRoom)

                self.rooms.sort(by: {
                    if $0.created_Date == nil
                    {
                        return false
                    }
                    if $1.created_Date == nil
                    {
                        return true
                    }

                    return $0.created_Date.compare($1.created_Date) == ComparisonResult.orderedDescending
                })

                self.tableView.reloadData()

            }
        }
    }

}

override func numberOfSections(in tableView: UITableView) -> Int {
    return 1
}

override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return rooms.count
}

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

    if (indexPath as NSIndexPath).row == 0 {
        let cell2 = tableView.dequeueReusableCell(withIdentifier: "featured", for: indexPath) as! featuredCell
        let room = rooms[(indexPath as NSIndexPath).row]
        cell2.configureCell(room)
        return cell2

    } else {

        let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath) as! ArticlesCell
        let room = rooms[(indexPath as NSIndexPath).row]
        cell.configureCell(room)
        return cell
}

数据

import Foundation
import Firebase
import FirebaseAuth


let roomRef = FIRDatabase.database().reference()

class Data {

static let dataService = Data()

fileprivate var _BASE_REF = roomRef
fileprivate var _ROOM_REF_ = roomRef.child("rooms")

fileprivate var _BASE_REF2 = roomRef
fileprivate var _ROOM_REF_2 = roomRef.child("contents")

var BASE_REF: FIRDatabaseReference {
    return _BASE_REF
}

var ROOM_REF: FIRDatabaseReference {
    return _ROOM_REF_
}

var storageRef: FIRStorageReference {
    return FIRStorage.storage().reference()
}

var fileURL: String!

func fetchData(_ callback: @escaping (Room) -> ()) {
    Data.dataService.ROOM_REF.observe(.childAdded, with: { (snapshot) in

        print("snapshot.value - \(snapshot))")
        let room = Room(key: snapshot.key, snapshot: snapshot.value as! Dictionary<String, AnyObject>)
        callback(room)
    })
}


}

---

谢谢你的帮助

在加载或滚动tableview期间使用异步下载时，这是tableview的正常行为。您只需在加载之前清除图像，并在图像数据下载一次后将其保存在缓存中，以获得高效的网络费用。如果不使用缓存，则在重新使用单元格时，tableview始终“重新下载”图像。请看例子

 public func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "cell") as! TableViewCell
    let urle = self.filteredFlats[indexPath.row].flatThumbnailImage?.imageDownloadURL
    if let url = urle
    {
       cell.imgv.image = nil

        if let imagefromCache = imageCache.object(forKey: url as AnyObject) as? UIImage
        {
            cell.imgv.image = imagefromCache

        }
        else
        {
            cell.imgv.image = nil
            let urlURL = URL(string: (url))

            URLSession.shared.dataTask(with: urlURL!, completionHandler: { (data, response, error) in
                if error != nil
                {
                    print(error.debugDescription)
                    return
                }
                DispatchQueue.main.async {
                    let imagetoCache = UIImage(data:data!)
                    self.imageCache.setObject(imagetoCache!, forKey: url as AnyObject)
                    cell.imgv.image = imagetoCache

                }
            }).resume()


        }

    }

    return cell



}

---

此代码是从我的项目中复制的。因此，我正在缓存已下载的图像。另外，当单元被重用时，我不会重新下载它。只是检查它是否被缓存。因此，您可以使用此方法来实现满足您需求的行为。

在重用单元格时，featuredImage.image仍可以与以前的图像一起加载。您应该确保configureCell内的if-else条件覆盖所有情况。例如，如果让imageURL=room.thumbnail失败，并且没有其他条件，featuredImage.image仍将与上一个图像一起加载。

 public func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "cell") as! TableViewCell
    let urle = self.filteredFlats[indexPath.row].flatThumbnailImage?.imageDownloadURL
    if let url = urle
    {
       cell.imgv.image = nil

        if let imagefromCache = imageCache.object(forKey: url as AnyObject) as? UIImage
        {
            cell.imgv.image = imagefromCache

        }
        else
        {
            cell.imgv.image = nil
            let urlURL = URL(string: (url))

            URLSession.shared.dataTask(with: urlURL!, completionHandler: { (data, response, error) in
                if error != nil
                {
                    print(error.debugDescription)
                    return
                }
                DispatchQueue.main.async {
                    let imagetoCache = UIImage(data:data!)
                    self.imageCache.setObject(imagetoCache!, forKey: url as AnyObject)
                    cell.imgv.image = imagetoCache

                }
            }).resume()


        }

    }

    return cell



}