如何将重新排序的Tableview单元格保存到核心数据 [英] How To Save Re-Ordered Tableview Cells To Core Data

问题描述

所以当我重新排序行时，我有了我的tableview，它会更新tableview以及所有内容，但不会保存到core data中.

So I have my tableview when I re-order my rows it updates the tableview and everything but it isn't saving to core data.

func tableView(_ tableView: UITableView, moveRowAt sourceIndexPath: IndexPath, to destinationIndexPath: IndexPath) {


    let appDelegate = UIApplication.shared.delegate as! AppDelegate
    let context = appDelegate.persistentContainer.viewContext
    let movedCampSites = itemName[sourceIndexPath.item]
    itemName.remove(at: sourceIndexPath.item)
    itemName.insert(movedCampSites, at: destinationIndexPath.item)
    context.delete(itemName[sourceIndexPath.row])
    context.insert(itemName[destinationIndexPath.row])

    do
    {
        try context.save()
    }
    catch
    {
        print("Could not move rows")
    }



}

一切正常，直到context.insert(itemName[destinationIndexPath.row])，例如，如果我注释掉并运行它，它将移动行并删除该行并保存到core data，但是context.insert不会保存新的行位置.由于某种原因，它正在运行我的catch块，因为我收到错误消息无法移动行".

Everything works up till context.insert(itemName[destinationIndexPath.row]) for example if I comment that out and run it, it will move the rows and delete the row and save to core data, but the context.insert doesn't save the new row position. For some reason it is running my catch block as I am getting the error Could not move rows.

这是控制台中的一些错误.

Here is some of the error that is in the console.

2018-07-22 09:27:01.884925-0700搜索栏核心数据[67957:5383630] [错误]错误:(1555)唯一约束失败:ZTITLE.Z_PK CoreData:错误:(1555)唯一约束失败:ZTITLE.Z_PK 无法移动行

2018-07-22 09:27:01.884925-0700 Search Bar Core Data[67957:5383630] [error] error: (1555) UNIQUE constraint failed: ZTITLE.Z_PK CoreData: error: (1555) UNIQUE constraint failed: ZTITLE.Z_PK Could not move rows

先谢谢了.

推荐答案

这是我对这个问题的看法:

Here is my take on this issue:

就像"vadian"说的那样，当您创建对象时，您会为附加到核心数据的数组添加一个属性，就像这样，

Like 'vadian' said, when you create an object you add a property for the array that appends to the Core Data, like this,

var itemsArray: [NSManagedObject] = []

save(sortOrder: itemsArray.count, item: itemTextField.text!) //Calling the save method wherever you need to, catching for example a UITextField user input

private func save(sortOrder: Int, item: String) {

    guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else { return }
    let context = appDelegate.persistentContainer.viewContext
    guard let entity = NSEntityDescription.entity(forEntityName: "CoreDataBaseName", in: context) else { return }
    let itemManagedObject = NSManagedObject(entity: entity, insertInto: context)

    itemManagedObject.setValue(sortOrder, forKeyPath: "sortOrder")
    itemManagedObject.setValue(item, forKeyPath: "item")

    do {
        try context.save()
        itemsArray.append(itemManagedObject)

    } catch let error as NSError {
        print("Could not save item to Core Data: \(error)")
    }
}

然后我们进入tableView的moveRowAt方法，

Then we come to the tableView's moveRowAt method,

override func tableView(_ tableView: UITableView, moveRowAt sourceIndexPath: IndexPath, to destinationIndexPath: IndexPath) {

    guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else { return }
    let context = appDelegate.persistentContainer.viewContext
    let movedItem = itemsArray[sourceIndexPath.row]

    itemsArray.remove(at: sourceIndexPath.row)
    itemsArray.insert(movedItem, at: destinationIndexPath.row)

    //This 'for-in loop' is at the heart of the solution
    for (i, item) in itemsArray.enumerated() {
        item.setValue(i, forKey: "sortOrder")
    }

    do {
        try context.save()
    } catch let error as NSError {
        print("Could not save/persist Core Data items in moveRowAt: \(error)")
    }
}

...在所有操作的最后，我们都使用

... And at the end of everything we fetch the rearranged order with,

private func fetch() {

    guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else { return }
    let context = appDelegate.persistentContainer.viewContext
    let fetchRequest = NSFetchRequest<NSManagedObject>(entityName: "CoreDataBaseName")
    let sortDescriptor = NSSortDescriptor(key: "sortOrder", ascending: true)

    fetchRequest.sortDescriptors = [sortDescriptor]

    do {
        itemsArray = try context.fetch(fetchRequest)
    } catch let error as NSError {
        print("Could not fetch Core Data entities: \(error)")
    }
}

您可以通过一百万种不同的方式来改进此想法(这总是很受欢迎)，但这是解决方案的教学示例.

There's a million different ways that you can improve this idea (which is always welcome), but this is a pedagogical example of a solution.

我希望它可以帮助某个人！

I hope it can help somebody out there!

这篇关于如何将重新排序的Tableview单元格保存到核心数据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IT屋！