拖放 - 检测我的模型类型标识符答案

【问题标题】：Drag and Drop - detect my Model type identifier拖放 - 检测我的模型类型标识符
【发布时间】：2018-01-24 09:24:00
【问题描述】：

我在我的UICollectionViewController 中实现drag and drop，它的数据源是我为测试目的创建的custom Model

Model 如下：

class UserClass: NSObject, NSItemProviderWriting, NSItemProviderReading {
    static var readableTypeIdentifiersForItemProvider: [String] { return [] }

    static func object(withItemProviderData data: Data, typeIdentifier: String) throws -> Self {
        return self.init(someData: "test")
    }

    static var writableTypeIdentifiersForItemProvider: [String] { return [] }

    func loadData(withTypeIdentifier typeIdentifier: String, forItemProviderCompletionHandler completionHandler: @escaping (Data?, Error?) -> Void) -> Progress? {
        return nil
    }

    required init(someData:String) {}
}

这是我的UICollectionViewDragDelegate

// This is the cv datasource
var myModel: [UserClass] = [userClass1, userClass2, userClass3, userClass4, ...]

// UICollectionViewDragDelegate

func collectionView(_ collectionView: UICollectionView, itemsForBeginning session: UIDragSession, at indexPath: IndexPath) -> [UIDragItem] {
    let item = myModel[indexPath.item]

    let itemProvider = NSItemProvider(object: item)
    let dragItem = UIDragItem(itemProvider: itemProvider)
    dragItem.localObject = item

    return [dragItem]
}

// To add multiple items for the drag session
func collectionView(_ collectionView: UICollectionView, itemsForAddingTo session: UIDragSession, at indexPath: IndexPath, point: CGPoint) -> [UIDragItem] {
    let item = myModel[indexPath.item]
    let itemProvider = NSItemProvider(object: item)
    let dragItem = UIDragItem(itemProvider: itemProvider)
    dragItem.localObject = item

    return [dragItem]
}

这是一个custom UIView，它将处理/接收丢弃：

class CustomView: UIView {
    override init(frame: CGRect) {
        super.init(frame: frame)            
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

extension CustomView: UIDropInteractionDelegate {
    func dropInteraction(_ interaction: UIDropInteraction, canHandle session: UIDropSession) -> Bool {
        return session.hasItemsConforming(toTypeIdentifiers: [""]) // <-- Which type is my model type ? 
    }

    func dropInteraction(_ interaction: UIDropInteraction, sessionDidUpdate session: UIDropSession) -> UIDropProposal {
        let dropLocation = session.location(in: self)
        let operation: UIDropOperation

        if self.frame.contains(dropLocation) {
            operation = session.localDragSession == nil ? .copy : .move
        } else {
            operation = .cancel
        }


        let dropProposal = UIDropProposal(operation: operation)
        dropProposal.isPrecise = true
        return dropProposal
    }

    func dropInteraction(_ interaction: UIDropInteraction, performDrop session: UIDropSession) {
        print("drop detected\n")

        session.loadObjects(ofClass: UserClass.self) { (objects) in
            objects.forEach({ (object) in
                print("object description:", object)
            })
        }
    }
}

拖动本身按预期工作，一个或多个项目响应拖动会话并被提升，但不知何故我的自定义视图没有检测到下降，它的任何功能都没有触发。

我认为可能是问题在于我不知道应该在此处设置哪个session.hasItemsConforming(tyTypeIdentifiers:[])，因为我不知道我的模型是哪种类型。

我可以帮忙吗？

【问题讨论】：

标签： ios swift drag-and-drop

【解决方案1】：

您可以通过以下方式决定哪种对象可以处理拖动：

所有对象：

func dropInteraction(_ interaction: UIDropInteraction, canHandle session: UIDropSession) -> Bool {
   return true
}

只接受CustomView类型的对象：

func dropInteraction(_ interaction: UIDropInteraction, canHandle session: UIDropSession) -> Bool {
   return session.canLoadObjects(ofClass: CustomView.self)
}

我猜后者更适合你的情况。

【讨论】：