iOS Swift Cache Image 簡易的Image Cache

簡單的Cache Image, 讓圖片不用一直下載,造成卡卡的問題

1.建立一個Project, 先在Info.plist ->右鍵 Open AS -> 選Source Code
在dict內加入,
NSAppTransportSecurity
NSAllowsArbitraryLoads 

2.接著建立MyTableViewCell.swift, 後面在Cell建立Image View後拉過來對應

class MyTableViewCell: UITableViewCell {

    @IBOutlet weak var iv: UIImageView!
    
    var ivUrl: NSURL! //圖片來源url
    
    override func awakeFromNib() {
        super.awakeFromNib()
        // Initialization code
    }

    override func setSelected(_ selected: Bool, animated: Bool) {
        super.setSelected(selected, animated: animated)

        // Configure the view for the selected state
    }

}

3.然後在Main.storyboard拉一個Table View

在cell裡面加個Image View, 對應Class: MyTableViewCell

Table View拉一下dataSource與delegate到ViewController

記得給Cell的Identifier,這裡寫ImageCell

4.建立一個CustomImageCache.swift檔案

import UIKit

class CustomImageCache {
    
    static let sharedCache: NSCache = { () -> NSCache<AnyObject, AnyObject> in
        let cache = NSCache<AnyObject, AnyObject>()
        cache.name = "MyImageCache"
        cache.countLimit = 20 // Max 20 images in memory.
        cache.totalCostLimit = 10*1024*1024 // Max 10MB used.
        return cache
    }()
    
}

extension NSURL {
    
    typealias ImageCacheCompletion = (UIImage) -> Void
    
    
    var cachedImage: UIImage? {
        return CustomImageCache.sharedCache.object(
            forKey: absoluteString as AnyObject) as? UIImage
    }
    
    func fetchImage(completion: @escaping ImageCacheCompletion) {
        // 如果需要客製化取得資料在此做
        let task = URLSession.shared.dataTask(with: self as URL) {
            data, response, error in
            if error == nil {
                if let data = data, let image = UIImage(data: data) {
                    CustomImageCache.sharedCache.setObject(
                        image,
                        forKey: self.absoluteString as AnyObject,
                        cost: data.count)
                    DispatchQueue.main.async() {
                        completion(image)
                    }
                }
            }
        }
        task.resume()
    }
    
}

5.最後在ViewController.swift

import UIKit

class ViewController: UIViewController, UITableViewDataSource, UITableViewDelegate {

    var url = [String]()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 重複50張圖片
        url = Array(repeating: "http://g03.a.alicdn.com/kf/HTB1hvNUIFXXXXbBXFXXq6xXFXXX2/3D-Diamond-Embroidery-Paintings-Rhinestone-Pasted-diy-Diamond-painting-cross-Stitch-font-b-coffe-b-font.jpg", count: 50)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return url.count
    }
    
    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

        let cell: MyTableViewCell = tableView.dequeueReusableCell(withIdentifier: "ImageCell") as! MyTableViewCell
        let ivUrl = NSURL(string: url[indexPath.row])
    
        cell.ivUrl = ivUrl // For recycled cells' late image loads.
        if let image = ivUrl?.cachedImage { //抓過了 -> 直接顯示
            cell.iv.image = image
            cell.iv.alpha = 1
        } else { //沒抓過 ->下載圖片
            cell.iv.alpha = 0
            // 下載圖片
            ivUrl?.fetchImage { image in
                // Check the cell hasn't recycled while loading.
                if cell.ivUrl == ivUrl {
                    cell.iv.image = image
                    UIView.animate(withDuration: 0.3) {
                        cell.iv.alpha = 1
                    }
                }
            }
        }
        
        return cell
    }
}

檔案下載:
https://github.com/terryyamg/CacheImag
參考來源:
http://www.splinter.com.au/2015/09/24/swift-image-cache/