iOS swift : Downcasting AnyObject

Question

我知道有人问了很多从 Cocoa 到 Swift 的向下转换问题，并且有一些错误，但是我已经尝试了很多在这里找到的方法，但我无法让它们工作，希望有人能伸出援手。

我是编程新手。我正在快速为 iOS 制作一个数据库程序。

我有一个人类:

class Person : NSObject {
    var firstName : String
    var lastName : String

    init (firstName : String, lastName : String) {
        self.firstName = firstName
        self.lastName = lastName
    }

    func encodeWithCoder(aCoder: NSCoder!) {
        aCoder.encodeObject(firstName, forKey:"firstName")
        aCoder.encodeObject(lastName, forKey:"lastName")
}

    init (coder aDecoder: NSCoder!) {
        self.firstName = aDecoder.decodeObjectForKey("firstName") as String
        self.lastName = aDecoder.decodeObjectForKey("lasName") as String
    }

}

我在 View Controller 的顶部声明了一个类数组:

    var peopleArray = [Person]()

然后我通过声明一些示例用户来填充数组并将其附加到数组:

    var nateB = Person(firstName: "Nate", lastName: "Birkholz")
    var nateC = Person(firstName: "Nate", lastName: "Carson")
    var nateD = Person(firstName: "Nate", lastName: "Donnelly")
    self.peopleArray.append(nateB)
    self.peopleArray.append(nateC)
    self.peopleArray.append(nateD)

然后我尝试将数据保存到 plist 文件中:

let fileManager = (NSFileManager.defaultManager())
        let directorys : [String]? = NSSearchPathForDirectoriesInDomains(NSSearchPathDirectory.DocumentDirectory,NSSearchPathDomainMask.AllDomainsMask, true) as? [String]

        println("value of directorys is \(directorys)")

        if (directorys != nil){
            let directories:[String] = directorys!;
            let pathToFile = directories[0]; //documents directory

            let plistfile = "PeopleArray.plist"
            let plistpath = pathToFile.stringByAppendingPathComponent(plistfile);

            if !fileManager.fileExistsAtPath(plistpath){  //writing Plist file

                self.createInitialPeople()

                println("Declaring cocoaArray")
                var cocoaArray : NSArray = [NSKeyedArchiver.archivedDataWithRootObject(peopleArray)]
                println("writing to path")
                cocoaArray.writeToFile(plistpath, atomically: true)
                let tellMe = cocoaArray.writeToFile(plistpath, atomically: true)
                println("Return of write is \(tellMe)")
            } 

创建了一个包含难以理解的数据的 Plist 文件。

我关闭应用程序并重新启动它，然后尝试加载文件:

         else {            
            println("\n\nPlist file found at \(plistpath)")

            let cocoaArray = NSMutableArray.arrayWithContentsOfFile(plistpath)
            peopleArray = cocoaArray as Array
        }
    }

我失败了，因为我无法向下转换“AnyObject 与‘Person’不相同。我已经尝试通过在 StackOverflow 上列出的几种方式向下转换它，但无法成功。这真的很令人沮丧。

更新最终代码:

func createPeoplePlist() {

    let fileManager = (NSFileManager.defaultManager())
    let directorys : [String]? = NSSearchPathForDirectoriesInDomains(NSSearchPathDirectory.DocumentDirectory,NSSearchPathDomainMask.AllDomainsMask, true) as? [String]

    println("value of directorys is \(directorys)")

    if (directorys != nil){
        let directories:[String] = directorys!;
        let pathToFile = directories[0]; //documents directory

        let plistfile = "PeopleArray.plist"
        plistpath = pathToFile.stringByAppendingPathComponent(plistfile);

        if !fileManager.fileExistsAtPath(plistpath){  //writing Plist file

            self.createInitialPeople()

            println("Saving to Plist")

            [NSKeyedArchiver.archiveRootObject(peopleArray, toFile: plistpath)]

            println("writing to path \(plistpath)")


        } else {            //Reading Plist file
            println("\n\nPlist file found at \(plistpath)")

            peopleArray = NSKeyedUnarchiver.unarchiveObjectWithFile(plistpath) as [Person]



        }
    }


}

Answer 1

当您读回数组时，您的数组仍然包含 NSData(您首先在归档时创建的数据)。但是，我会质疑为什么在写入磁盘之前甚至将数据放在另一个数组中。 peopleArray 本身可以是根对象；不需要额外的数组来包装它。然后你可以简单地使用 archiveRootObject(_:toFile:) 和 unarchiveObjectWithFile(_:)。

我还建议阅读 Archives and Serializations Programming Guide和 Property List Programming Guide , 和 NSKeyedArchiver文档，以获取更多信息。