Swift中的核心数据

Swift中的核心数据

本文介绍了Swift中的核心数据:只保存for循环中的最后一个对象的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!

问题描述

我试图在Core Data中将多个对象保存到IPodSongs实体中 for 循环中,即当前在 for song in result {} 循环。但是我的代码只保存循环中的最后一首歌,只是不断覆盖同一个对象。而不是覆盖相同的对象,我需要每次创建一个新的对象。我做错了什么?

I'm trying to save multiple objects in Core Data to the IPodSongs entity in a for loop, namely the title of the song currently in the for song in result{} loop. But my code only saves the very last song in the loop, and just keeps overwriting the same object. Instead of overwriting the same object, I need to create a new object each time. What am I doing wrong?

func fetchiPodSongsOnSignup() {

        var appDel: AppDelegate = UIApplication.sharedApplication().delegate as! AppDelegate

        var context: NSManagedObjectContext = appDel.managedObjectContext!

        var newSong = NSEntityDescription.insertNewObjectForEntityForName("IPodSongs", inManagedObjectContext: context) as! NSManagedObject

        var request = NSFetchRequest(entityName: "IPodSongs")

        request.returnsObjectsAsFaults = false

        var results = context.executeFetchRequest(request, error: nil)


        let query = MPMediaQuery.songsQuery()

        let result = query.collections as! [MPMediaItemCollection]

        for song in result {

            for song in song.items as! [MPMediaItem] {

                newSong.setValue("\(song.valueForProperty(MPMediaItemPropertyTitle))", forKey: "title")

                println(newSong)

                context.save(nil)

            }
        }


推荐答案

您不需要创建将新对象保存到Core Data的请求。你做错了是创建一个单一的托管对象,插入它,然后改变它通过循环,而不是为每首歌曲创建一个新的对象。

You dont need to create a request to save new objects to Core Data. What you did wrong was create a single managed object, inserted it and then changeded it through the loop instead of creating a new object for each song.

工作

func fetchiPodSongsOnSignup() {

    var appDel: AppDelegate = UIApplication.sharedApplication().delegate as! AppDelegate

    var context: NSManagedObjectContext = appDel.managedObjectContext!


    let query = MPMediaQuery.songsQuery()

    let result = query.collections as! [MPMediaItemCollection]

    for song in result {

        for song in song.items as! [MPMediaItem] {

            var newSong = NSEntityDescription.insertNewObjectForEntityForName("IPodSongs", inManagedObjectContext: context) as NSManagedObject

            newSong.setValue("\(song.valueForProperty(MPMediaItemPropertyTitle))", forKey: "title")

            println(newSong)


        }
    }
    if context.save(&errorPointer == false {
        printlin("Error received while saving")
    }

}

如果context.save(& errorPointer == false {printlin(保存时收到错误)}} 最后。

Also put if context.save(&errorPointer == false {printlin("Error received while saving")} at the very end.

这篇关于Swift中的核心数据:只保存for循环中的最后一个对象的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!

09-02 05:33