你能在核心數據中保存一組圖像嗎？

Question

我知道您可以使用實體的二進制數據屬性保存一個，但是否可以保存多個？

您可以使用以下方法保存一個：

UIImageJPEGRepresentation(image: UIImage)

您可以保存它，然后再次將其轉換為圖像

UIImage(data: ____)

但是我可以將一個充滿圖像的數組轉換為二進制數據嗎？

如果您不能使用核心數據，還有其他方法可以做到嗎？

順便說一句，圖像陣列充滿了保存在設備上的用戶拍攝的圖像。

感謝所有的幫助者！

Answer 1

將您的數組轉換為NSMutableArray並將其存檔為NSData

var imgArray = [UIImage]();

var CDataArray = NSMutableArray();

for img in imgArray{
    let data : NSData = NSData(data: UIImagePNGRepresentation(img))
    CDataArray.addObject(data);
}

//convert the Array to NSData
//you can save this in core data
var coreDataObject = NSKeyedArchiver.archivedDataWithRootObject(CDataArray);

從 CData 拉取后，提取數據：

//extract:
if let mySavedData = NSKeyedUnarchiver.unarchiveObjectWithData(coreDataObject) as? NSArray{
    //extract data..
}

斯威夫特 5

現在不推薦使用一些方法。 以下代碼適用於 Swift 5：

func coreDataObjectFromImages(images: [UIImage]) -> Data? {
    let dataArray = NSMutableArray()
    
    for img in images {
        if let data = img.pngData() {
            dataArray.add(data)
        }
    }
    
    return try? NSKeyedArchiver.archivedData(withRootObject: dataArray, requiringSecureCoding: true)
}

func imagesFromCoreData(object: Data?) -> [UIImage]? {
    var retVal = [UIImage]()

    guard let object = object else { return nil }
    if let dataArray = try? NSKeyedUnarchiver.unarchivedObject(ofClass: NSArray.self, from: object) {
        for data in dataArray {
            if let data = data as? Data, let image = UIImage(data: data) {
                retVal.append(image)
            }
        }
    }
    
    return retVal
}

Answer 2

基於 daniel-krom 的回答，我創建了一個 swift 擴展，以便輕松添加到模型對象：

let coreDataObject = imgArray.coreDataRepresentation()

if let retrievedImgArray = coreDataObject?.imageArray() {
    // use retrievedImgArray
}

這是擴展名

import UIKit

typealias ImageArray = [UIImage]
typealias ImageArrayRepresentation = Data

extension Array where Element: UIImage {
    // Given an array of UIImages return a Data representation of the array suitable for storing in core data as binary data that allows external storage
    func coreDataRepresentation() -> ImageArrayRepresentation? {
        let CDataArray = NSMutableArray()

        for img in self {
            guard let imageRepresentation = UIImagePNGRepresentation(img) else {
                print("Unable to represent image as PNG")
                return nil
            }
            let data : NSData = NSData(data: imageRepresentation)
            CDataArray.add(data)
        }

        return NSKeyedArchiver.archivedData(withRootObject: CDataArray)
    }
}

extension ImageArrayRepresentation {
    // Given a Data representation of an array of UIImages return the array
    func imageArray() -> ImageArray? {
        if let mySavedData = NSKeyedUnarchiver.unarchiveObject(with: self) as? NSArray {
            // TODO: Use regular map and return nil if something can't be turned into a UIImage
            let imgArray = mySavedData.flatMap({
                return UIImage(data: $0 as! Data)
            })
            return imgArray
        }
        else {
            print("Unable to convert data to ImageArray")
            return nil
        }
    }
}