ios - 核心数据的 Collection View - 最后选择的内容首先出现

Question

当前功能

我有一个 Collection View ，其中每个单元格都由图像和标签组成。它是 View Controller 中的 Collection View 。目前，该 View 可以从两个数组(一个用于图像名称，一个用于标签名称)编译和加载。当用户点击一个单元格时，它会将他们带到一个新的 View Controller 。

期望的功能

但是，我想添加这样的功能，当用户返回到 Collection View 时，他们点击的单元格现在是第一个(左上角位置)。此新订单应保存到核心数据并成为新的默认订单。

迄今为止的进展

我已经开始尝试实现此功能，但事实证明将原始数组放入 CoreData 具有挑战性。我无法将原始数组放入 CoreData 中，也无法从 CoreData 提取中构建 collectionView。 Collection View 构建但我的图像/标签都不存在，只有一些 CoreData 代码加载到我的标签中......

这是我在 viewDidLoad 中得到的:

    //Fetch & sort the list from Core Data
    let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
    let managedContext = appDelegate.managedObjectContext!
    let fetchRequest = NSFetchRequest(entityName: "MenuItem_llcv")
    let sortDescriptor = NSSortDescriptor(key: "displayOrder", ascending: true )
    fetchRequest.sortDescriptors = [ sortDescriptor ]
    var error: NSError?
    let fetchedResults = managedContext.executeFetchRequest(fetchRequest, error: &error) as? [NSManagedObject]

    //Check fetch results
    //If fetch was successful, the results are assigned to the context object
    if let results = fetchedResults {
        ll_ColViewOrder_Context = results
        println("Fetch succesful, although possibly empty.")
    } else {
        println("Could not fetch \(error), \(error!.userInfo)")
    }

    //First-time user check
    //If CoreData has the arrays, do nothing. If it doesn't, load them in.
    if ll_ColViewOrder_Context.count > 8 {
        println("Fetch result: Previously stored list found in Core Data.")
    } else {
        //Set arrays to populate cells
        cvListNames = ["Label 1", "Label 2", "Label 3", "Label 4", "Label 5"]

        cvListImgs = ["image1","image2","image3","image4","image5"]

        let entityVar =  NSEntityDescription.entityForName("MenuItem_llcv", inManagedObjectContext: managedContext)
        let listItem = NSManagedObject(entity: entityVar!, insertIntoManagedObjectContext:managedContext)

        var numberToStore = 1

        for ea_Name in cvListNames {
            listItem.setValue(ea_Name, forKey: "name")
        }
        for ea_ImgName in cvListImgs {
            listItem.setValue(ea_ImgName, forKey: "imgName")
        }
        for ea_OrderNum in cvListImgs {
            listItem.setValue(numberToStore, forKey: "displayOrder")
            ++numberToStore
        }
        managedContext.save(nil)
        println("Context now contains \(ll_ColViewOrder_Context)")
    }

这是我的表格构建的依据:

func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {

    let cell = collectionView.dequeueReusableCellWithReuseIdentifier(reuseIdentifier, forIndexPath: indexPath) as! LifeList_CollectionViewCell

    //Assign images
    let image = UIImage(named: "\(ll_ColViewOrder_Context[indexPath.row])")
    cell.cvCell_Image.image = image

    //Assign list names
    let title = "\(ll_ColViewOrder_Context[indexPath.row])"
    cell.cvCell_Name.text = title

Answer 1

您只创建了一个 NSManagedObject，然后通过为它的每个属性分配值来迭代。但你仍然只有一个对象。您需要为数组中的每个值创建一个新的 NSMO:

    //Set arrays to populate cells
    cvListNames = ["Label 1", "Label 2", "Label 3", "Label 4", "Label 5"]
    cvListImgs = ["image1","image2","image3","image4","image5"]

    let entityVar =  NSEntityDescription.entityForName("MenuItem_llcv", inManagedObjectContext: managedContext)

    for (index, value) in enumerate(cvListNames) {
        let listItem = NSManagedObject(entity: entityVar!, insertIntoManagedObjectContext:managedContext)
        listItem.setValue(value, forKey: "name")
        let imageName = cvListImgs[index]
        listItem.setValue(imageName, forKey: "imgName")
        listItem.setValue(index, forKey: "displayOrder")
        ll_ColViewOrder_Context.append(listItem)
    }
    managedContext.save(nil)
    println("Context now contains \(ll_ColViewOrder_Context)")

我使用了 enumerate 函数来获取 cvListNames 中每个值的 index。然后可以使用此 index 在 cvListImgs 中查找相应的图像，并填充 displayOrder 属性。我还添加了一行代码，用于将每个新的 NSMO 附加到支持您的 Collection View 的数组。

此外，在填充 Collection View 的代码中，您需要使用valueForKey 来提取相关属性的值:

let cell = collectionView.dequeueReusableCellWithReuseIdentifier(reuseIdentifier, forIndexPath: indexPath) as! LifeList_CollectionViewCell
//Assign images
let currentObject = ll_ColViewOrder_Context[indexPath.row]
let imageName = currentObject.valueForKey("imgName")
let listName = currentObject.valueForKey("name")
let image = UIImage(named: imageName)
cell.cvCell_Image.image = image
//Assign list names
cell.cvCell_Name.text = listName