查看特定属性的所有记录并查看最高值

Question

好的，所以我有一个专为角色扮演而设计的应用程序。我有一个指导用户创建角色的指南。所以用户要做的第一件事就是输入字符编号。所以我希望它搜索我称为characternumber 的属性的所有记录，并查看最大的数字是多少。

示例：假设我有 5 个字符。字符编号为 1,2,3,4,5。我想循环浏览所有记录并看到 5 是最大的数字，而不是自动在字符数文本字段中放置 6。

这是我目前所拥有的：

 @IBOutlet var societyNumberTxt: UITextField!
    @IBOutlet var characterNumberTxt: UITextField!

    let managedObjectContext = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext

    var characters: [NSManagedObject] = []
    var societyNum: [NSManagedObject] = []
    var charNum: [String] = []

    override func viewDidLoad()
    {
        super.viewDidLoad()

        //1
        guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else {
            return
        }

        let managedContext = appDelegate.persistentContainer.viewContext

        //2
        let fetchRequest = NSFetchRequest<NSManagedObject>(entityName: "Characters")

        //3
        do {
            societyNum = try managedContext.fetch(fetchRequest)

            let entityDescription = NSEntityDescription.entity(forEntityName: "Characters", in: managedObjectContext)

            let request: NSFetchRequest<Characters> = Characters.fetchRequest()
            request.entity = entityDescription

            var results = try managedObjectContext.fetch(request as! NSFetchRequest<NSFetchRequestResult>)

            if societyNum.count > 0
            {
                let match = results[0] as! NSManagedObject
                societyNumberTxt.text = (match.value(forKey: "societynumber") as? String)!
                print(match)

                if (match.value(forKey: "characternumber") != nil)
                {
                    self.charNum = match.value(forKey: "characternumber") as! [String]
                    print(self.charNum)
                }
                else
                {
                    print("empty array")
                    characterNumberTxt.text = "1"
                }
            }
            else
            {
                societyNumberTxt.placeholder = "Society # not set"
            }

        } catch let error as NSError {
            print("Could not fetch. \(error), \(error.userInfo)")
        }

    }

我不确定如何循环遍历每条记录并检查数组中的属性和位置。我尝试过这样的事情：

var i = 0

for i in results
{
    var match = results[i] as? NSManagedObject
    charNum[i] = match
}

我得到了错误：
不能使用“Any”类型的索引为“[Any]”类型的值下标

现在来测试我的 if 语句代码：

if (match.value(forKey: "characternumber") != nil)
{
    self.charNum = match.value(forKey: "characternumber") as! [String]
    print(self.charNum)
}

返回错误：
无法将“NSTaggedPointerString”（0x108578d10）类型的值转换为“NSArray”（0x108578dd8）。

我什至是正确的过去吗？

Answer 1

使用SortDescriptor 调整您的获取请求，而不是手动查找最高的characterNumber：

...

//2
// get all characters ...
let fetchRequest = NSFetchRequest<NSManagedObject>(entityName: "Characters")

// ... sorted by characternumber in acending order
let sortDescriptor = NSSortDescriptor(key: "characternumber", ascending: true)
let sortDescriptors = [sortDescriptor]
fetchRequest.sortDescriptors = sortDescriptors

//3
do {
    let characters = try managedContext.fetch(fetchRequest) as! [Characters]
    if let  highestCharacterNumber = characters.last?.characternumber {
        characterNumberTxt.text = String(highestCharacterNumber + 1) // assuming characternumber is of type Int
    } else {
        characterNumberTxt.text = "1"
    }
} ...