Question

我有以下代码来访问Core Data数据库并检索字符串。（格式化为xx：xx：xx）

我的目标是遍历时间（String）以找到最大的持续时间。我的代码如下：

func loadHighscore() {
    let appDel:AppDelegate = (UIApplication.sharedApplication().delegate as! AppDelegate)
    let context = appDel.managedObjectContext

    var score = NSFetchRequest(entityName: "Scores")
    score.returnsObjectsAsFaults = false

    var scores : NSArray = context!.executeFetchRequest(score, error: nil)!

    println("\(scores.count) scores available")

    var highestMins = 0
    var highestSecs = 0
    var highestFrac = 0

    var currentMins : Int
    var currentSecs : Int
    var currentFrac : Int

    if scores.count > 0 {

        var time = scores.firstObject!
        var myStringArr = time.componentsSeparatedByString(":")

        currentMins = myStringArr[0] as! Int
        currentSecs = myStringArr[1] as! Int
        currentFrac = myStringArr[2] as! Int

        if currentMins > highestMins {
            highestMins = currentMins
            highestSecs = currentSecs
            highestFrac = currentFrac
        }

        else if currentMins ==  highestMins {
            if currentSecs > highestSecs {
                highestMins = currentMins
                highestSecs = currentSecs
                highestFrac = currentFrac
            }
            else if currentSecs == highestSecs {
                if currentFrac > highestFrac {
                    highestMins = currentMins
                    highestSecs = currentSecs
                    highestFrac = currentFrac
                }
                    //accounts for the times being identical
                else {
                    highestMins = currentMins
                    highestSecs = currentSecs
                    highestFrac = currentFrac
                }
            }
        }

        println("Highscore: \(highestMins):\(highestSecs):\(highestFrac)")
    }
    else {
        println("0 scores returned")
    }

}

当我遵守此规则时，我收到了错误

'由于未捕获的异常'NSInvalidArgumentException'，原因： ' - [NSManagedObject componentsSeparatedByString：]：无法识别选择器发送到实例'。

我认为这可能是因为我没有正确地从Core Data数据库中获取/拆分字符串值。

如何正确检索此字符串的任何想法都将非常感激！

Answer 1

CoreData无法存储字符串。它只存储NSManagedObjects。您执行的获取的结果是NSManagedObjects的列表。您需要创建一个带有字段的实体来存储时间。

例如，在xcdatamodeld中创建一个名为Score的实体，其字段类型为String，称为time。

然后，在您的代码中，执行以下操作：

        (...)
        var score = NSFetchRequest(entityName: "Score")
        score.returnsObjectsAsFaults = false

        var scores : NSArray = context!.executeFetchRequest(score, error: nil)!

        println("\(scores.count) scores available")

        var highestMins = 0
        var highestSecs = 0
        var highestFrac = 0

        var currentMins : Int
        var currentSecs : Int
        var currentFrac : Int

        for score in scores {

            var time = score.valueForKey("time") as! String
            var myStringArr = time.componentsSeparatedByString(":")
        (...)

从Core Data Swift中检索字符串

1 个答案: