在 SwiftUI 中将加载的 json 文件中的更改保存到 Core Data

Question

我想用 json 文件加载我的数据。到现在为止还挺好。但现在我很挣扎。如果用户对油对象进行了一些更改并想要保存它们怎么办？我的想法是，我将更改后的油对象保存到 CoreData。但这有什么可能？因为每次用户启动应用程序时，都会加载未修改的 json 文件，并且用户不会看到他更改的对象。我该如何处理？还是我的想法不对？

struct Oil: Codable, Hashable, Identifiable {
    var id: Int
    
    let image: String
    let color: String
    
    let title: String
    let subtitle: String
    let description: String
    
    var localizedTitle: LocalizedStringKey {
        return LocalizedStringKey(title)
    }
    var localizedDescription: LocalizedStringKey {
        return LocalizedStringKey(description)
    }
    
    var isFavorite: Bool
    
    static let exampleOil = Oil(id: 10001, image: "",color: "lavenderColor" ,title: "lavender", subtitle: "Lavandula angustifolia", description: "", isFavorite: false)
    
}

final class Oils: ObservableObject {
    
    var oils: [Oil] = load("oilDatabase.json")
}


func load<T: Decodable>(_ filename: String) -> T {
    let data: Data

    guard let file = Bundle.main.url(forResource: filename, withExtension: nil)
    else {
        fatalError("Couldn't find \(filename) in main bundle.")
    }

    do {
        data = try Data(contentsOf: file)
    } catch {
        fatalError("Couldn't load \(filename) from main bundle:\n\(error)")
    }

    do {
        let decoder = JSONDecoder()
        return try decoder.decode(T.self, from: data)
    } catch {
        fatalError("Couldn't parse \(filename) as \(T.self):\n\(error)")
    }
}

Answer 1

你真的需要核心数据吗？如果您只是存储一个 json 文件，您可以节省很多复杂性，只需将文件的更新版本写入文档目录。

您所要做的就是检查文件是否存在于文档目录中，如果它确实从那里加载它，否则从您的包中加载它。

这将获取文档目录的 URL

func getDocumentsDirectory() -> URL {
    let paths = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
    return paths[0]
}

然后我们只需要更新您的load 以在加载之前检查文件是否存在于文档目录中。

func load<T: Decodable>(_ filename: String) -> T {
    let data: Data

    // Check that the fileExists in the documents directory
    let filemanager = FileManager.default
    let localPath = getDocumentsDirectory().appendingPathComponent(filename)

    if filemanager.fileExists(atPath: localPath.path) {
        
        do {
            data = try Data(contentsOf: localPath)
        } catch {
           fatalError("Couldn't load \(filename) from documents directory:\n\(error)")
        }

    } else {
        // If the file doesn't exist in the documents directory load it from the bundle
        guard let file = Bundle.main.url(forResource: filename, withExtension: nil)
        else {
            fatalError("Couldn't find \(filename) in main bundle.")
        }

        do {
            data = try Data(contentsOf: file)
        } catch {
            fatalError("Couldn't load \(filename) from main bundle:\n\(error)")
        }
    }


    do {
        let decoder = JSONDecoder()
        return try decoder.decode(T.self, from: data)
    } catch {
        fatalError("Couldn't parse \(filename) as \(T.self):\n\(error)")
    }
}

您还需要保存对 json 所做的任何更改。您可以使用以下函数来做到这一点。

func save<T: Encodable>(_ filename: String, item: T) {

    let encoder = JSONEncoder()
    do {
        let url = getDocumentsDirectory().appendingPathComponent(filename)
        let encoded = try encoder.encode(item)
        let jsonString = String(data: encoded, encoding: .utf8)
        try jsonString?.write(to: url, atomically: true, encoding: .utf8)
    } catch {
        // handle your error
    }
}