Swift 3: Convenience methods to load and save an NSCoding object from the iOS directories.

IOSDirectoryFile

import Foundation

protocol IOSDirectoryFile {
    static var dirSelector: FileManager.SearchPathDirectory { get }
}

extension IOSDirectoryFile {
    
    static var url: URL {
        return FileManager.default.urls(for: dirSelector, in: .userDomainMask)[0]
    }

    static func path(_ fileName: String) -> String {
        return url.appendingPathComponent(fileName).path
    }
    
    static func load(_ fileName: String) -> Any? {
        let fullPath = path(fileName)
        return NSKeyedUnarchiver.unarchiveObject(withFile: fullPath)
    }
    
    static func save(_ object: Any, fileName: String) {
        // may fail because it may not exist in sandbox, so check existence and create if necessary
        if !FileManager.default.fileExists(atPath: url.absoluteString) {
            try? FileManager.default.createDirectory(at: url, withIntermediateDirectories: true, attributes: nil)
        }
        let fullPath = path(fileName)
        let b = NSKeyedArchiver.archiveRootObject(object, toFile: fullPath)
        if !b {
            print("Failed saving \(fullPath)")
        }
    }
    
    static func remove(_ fileName: String) {
        let fullPath = path(fileName)
        try? FileManager.default.removeItem(atPath: fullPath)
    }
}

/// Example usage:
/// - AppSupportFile.load("name.txt")
/// - AppSupportFile.save(fileContents, fileName: "name.txt")
/// - AppSupportFile.remove("name.txt")
class AppSupportFile: IOSDirectoryFile {
    static var dirSelector: FileManager.SearchPathDirectory { return .applicationSupportDirectory }
}

/// Example usage:
/// - DocumentsFile.load("name.txt")
/// - DocumentsFile.save(fileContents, fileName: "name.txt")
/// - DocumentsFile.remove("name.txt")
class DocumentsFile: IOSDirectoryFile {
    static var dirSelector: FileManager.SearchPathDirectory { return .documentDirectory }
}

Example usage:

AppSupportFile.load("name.txt")
AppSupportFile.save(fileContents, fileName: "name.txt")
AppSupportFile.remove("name.txt")

or

DocumentsFile.load("name.txt")
DocumentsFile.save(fileContents, fileName: "name.txt")
DocumentsFile.remove("name.txt")