图像未显示在 UICollectionViewCell 中

Question

我正在使用 UIKIT 和 Swift 制作一个 iOS 电影应用程序，我想在 collectionview 中显示电影，但是出现了某种故障，并且显示的是某种类型的电影而不是电影。 有人可以帮忙吗？谢谢

moviesViewController.swift

//
//  FirstViewController.swift
//  PopcornTime
//
//  Created by Maxime Ruys on 15/03/2020.
//  Copyright © 2020 Pixel-Developers. All rights reserved.
//

import UIKit
import SwiftyJSON

class MoviesViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate {

    @IBOutlet weak var moviesCollectionView: UICollectionView!

    var movies = [Movie]()

    override func viewDidLoad() {
        super.viewDidLoad()

        self.moviesCollectionView.delegate = self
        self.moviesCollectionView.dataSource = self

        fetchMovies()

    }

    func fetchMovies(){

        self.movies = []

        let url = URL(string: "API_URL_HERE")

        guard let requestUrl = url else { fatalError() }

        var request = URLRequest(url: requestUrl)
        request.httpMethod = "GET"

        request.httpBody = "".data(using: String.Encoding.utf8)

        let task = URLSession.shared.dataTask(with: request) { (data, response, error) in

            if (error != nil) {
                print(error)
            } else {

                if let data = data, let dataString = String(data: data, encoding: .utf8) {

                    do {

                        if let dataFromString = dataString.data(using: .utf8, allowLossyConversion: false) {

                            let json = try JSON(data: dataFromString)

                            for(_, movie) in json{

                                var imgs = [String]()

                                imgs.append(movie["images"]["banner"].stringValue)
                                imgs.append(movie["images"]["poster"].stringValue)
                                imgs.append(movie["images"]["fanart"].stringValue)

                                self.movies.append(Movie(id: movie["_id"].stringValue, title: movie["title"].stringValue, desc: movie["synopsis"].stringValue, playTime: movie["runtime"].stringValue, imgs: imgs))

                            }

                        }

                    } catch {
                        print(error)
                    }

                    DispatchQueue.main.async {
                        self.moviesCollectionView.reloadData()
                    }

                }

            }

        }

        task.resume()

    }

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return self.movies.count
    }

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

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

        cell.moviesRowImg.image = downloadImage(from: URL(string: movies[indexPath.row].imgs[0])!)
        cell.moviesTitleLbl.text = movies[indexPath.row].title

        return cell

    }

    func downloadImage(from url: URL) -> UIImage{
        getData(from: url) { data, response, error in
            guard let data = data, error == nil else { return }
            DispatchQueue.main.async() {
                return UIImage(data: data)
            }
        }
        return UIImage(named: "test")!
    }

    func getData(from url: URL, completion: @escaping (Data?, URLResponse?, Error?) -> ()) {
        URLSession.shared.dataTask(with: url, completionHandler: completion).resume()
    }

}

collectionview 故障图像：

collectionview 属性：

colletionview 单元格属性：

Answer 1

你不能分配一个异步的值，所以这里的 return 是 nil

func downloadImage(from url: URL) -> UIImage{
    getData(from: url) { data, response, error in
        guard let data = data, error == nil else { return }
        DispatchQueue.main.async() {
            return UIImage(data: data)
        }
    }
    return UIImage(named: "test")
}

使用SDWebImage

Answer 2

你可以像下面这样进行自省。

if movies[indexPath.row].imgs.count>0, let url = URL(string: movies[indexPath.row].imgs[0]!) {
    }

如果您希望缓存图像以避免多次请求，请使用以下扩展。

let imageCache = NSCache<NSString, UIImage>()

extension UIImageView {

func imageFromServerURL(_ URLString: String, placeHolder: UIImage?) {

    self.image = nil
    if let cachedImage = imageCache.object(forKey: NSString(string: URLString)) {
        self.image = cachedImage
        return
    }

    if let url = URL(string: URLString) {
        URLSession.shared.dataTask(with: url, completionHandler: { (data, response, error) in

            //print("RESPONSE FROM API: \(response)")
            if error != nil {
                print("ERROR LOADING IMAGES FROM URL: \(error)")
                DispatchQueue.main.async {
                    self.image = placeHolder
                }
                return
            }
            DispatchQueue.main.async {
                if let data = data {
                    if let downloadedImage = UIImage(data: data) {
                        imageCache.setObject(downloadedImage, forKey: NSString(string: URLString))
                        self.image = downloadedImage
                    }
                }
            }
        }).resume()
    }
}}

Answer 3

您的手机也未注册：

    self.collectionView.register(UICollectionViewCell.self, forCellReuseIdentifier: "movieCell")