Question

我正在尝试在我的tableview中加载图像异步，以便能够“离线”读取它们。

当我有连接时，图像会正确显示。否则，当我没有任何联系时它不会因此不起作用。。。

这是我正在使用的代码：

 import UIKit
 import FirebaseAuth
 import FirebaseDatabase
 import FirebaseStorage
 import SwiftKeychainWrapper
 import SwiftyJSON

 var posts = [Post]()
 var selectedIndexPath: Int = 10

 class FeedVC: UIViewController, UITableViewDataSource, 
 UIImagePickerControllerDelegate, UINavigationControllerDelegate, 
 UITableViewDelegate {

@IBOutlet weak var feedTableView: UITableView!

private var readPosts: ObserveTask?

override func viewDidLoad() {
    super.viewDidLoad()

    feedTableView.dataSource = self
    feedTableView.delegate = self

    readPosts = Post.observeList(from: Post.parentReference.queryOrdered(byChild: "privacy").queryEqual(toValue: false))

    {
        observedPosts in

        posts = observedPosts.reversed()
        self.feedTableView.reloadData()
    }
}

override var prefersStatusBarHidden: Bool {
    return true
}

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

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

func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
    return UITableViewAutomaticDimension
}

func tableView(_ tableView: UITableView, estimatedHeightForRowAt indexPath: IndexPath) -> CGFloat {
    return UITableViewAutomaticDimension
}


func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell  {
    let cell = self.feedTableView.dequeueReusableCell(withIdentifier: "MessageCell")! as UITableViewCell


 let imageView = cell.viewWithTag(1) as! CustomImageView



    let titleLabel = cell.viewWithTag(2) as! UILabel
    let linkLabel = cell.viewWithTag(3) as! UILabel

    titleLabel.text = posts[indexPath.row].title
    titleLabel.numberOfLines = 0

    linkLabel.text = posts[indexPath.row].link
    linkLabel.numberOfLines = 0



    Storage.getImage(with: posts[indexPath.row].imageUrl){
        postPic in
        imageView.image = postPic
    }

    return cell




}


func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    guard posts[indexPath.row].title != "COMING SOON" else {
        return
    }
           selectedIndexPath = indexPath.row
          self.performSegue(withIdentifier: "push", sender: self)
            self.feedTableView.reloadData()    }



 }

 let imageCache = NSCache<AnyObject, AnyObject>()

 class CustomImageView: UIImageView{

 var imageUrlString: String?

 func loadImageUsingUrlString(urlString: String){

    imageUrlString = urlString

    let url = NSURL(string: urlString)

    image = nil

    if let imageFromCache = imageCache.object(forKey: urlString as AnyObject) as? UIImage{

        self.image = imageFromCache
        return

    }

    URLSession.shared
        .dataTask(with: url! as URL, completionHandler:
            {(data, respones, error) in

                if error != nil{
                    print(error)



                    return
                }

                DispatchQueue.main.sync(execute: {

                    let imageToCache = UIImage(data: data!)

                    if self.imageUrlString == urlString{

                    self.image = imageToCache

                    }

                    imageCache.setObject(imageToCache!, forKey: urlString as AnyObject)

                    self.image = imageToCache
                }
                )

        }).resume()

}

 }

我正在使用类Class CustomImageView中的异步函数。

我通常是通过以下方式调用图片：

Storage.getImage(with: posts[indexPath.row].imageUrl){
    postPic in
    imageView.image = postPic
}

我想问题来自那部分？（我不是sur）

有没有人对我的过程中有什么问题有任何重点？

非常感谢你的帮助!!

- 编辑 -

通过以下方式调用图像存储：

 import Foundation
 import FirebaseStorage
 import UIKit

 let STORAGE_BASE = FIRStorage.storage().reference()

 class Storage
 {
static let REF_POST_IMAGES = STORAGE_BASE.child("post-pics")
static let REF_USER_IMAGES = STORAGE_BASE.child("user-pics")

static let imageCache: NSCache<NSString, UIImage> = NSCache()

static func upload(image: UIImage, to reference: FIRStorageReference, completionHandler: @escaping (String?, Error?) -> ())
{
    // Uploads the image
    if let imageData = UIImageJPEGRepresentation(image, 0.2)
    {
        let imageUid = NSUUID().uuidString
        let metadata = FIRStorageMetadata()
        metadata.contentType = "image/jpeg"

        reference.child(imageUid).put(imageData, metadata: metadata)
        {
            (metadata, error) in

            if let error = error
            {
                completionHandler(nil, error)
            }

            if let downloadURL = metadata?.downloadURL()?.absoluteString
            {
                // Caches the image for faster display
                imageCache.setObject(image, forKey: downloadURL as NSString)
                completionHandler(downloadURL, nil)
            }
        }
    }
    else
    {
        completionHandler(nil, StorageError.compressionFailed)
    }
}

// Storage.imageCache.object(forKey: post.imageUrl as NSString)
static func getImage(with url: String, completionHandler: @escaping (UIImage) -> ())
{
    if let image = imageCache.object(forKey: url as NSString)
    {
        completionHandler(image)
    }
    else
    {
        let ref = FIRStorage.storage().reference(forURL: url)
        ref.data(withMaxSize: 2 * 1024 * 1024)
        {
            (data, error) in

            if let error = error
            {
                print("STORAGE: Unable to read image from storage \(error)")
            }
            else if let data = data
            {
                print("STORAGE: Image read from storage")
                if let image = UIImage(data: data)
                {
                    // Caches the image
                    Storage.imageCache.setObject(image, forKey: url as NSString)
                    completionHandler(image)
                }
            }
        }
    }
}
 }

 enum StorageError: Error
 {
case compressionFailed
 }

在Swift for iOS应用程序中加载异步图像不起作用

0 个答案: