如何使拖放视图修改器接受任何对象

Question

我创建了一个按预期工作的拖放视图修改器，但现在我想让它接受任何对象。我可以将添加到所有函数、结构和视图修饰符，但是当我尝试将它添加到我的单例 class 时，我得到“泛型类型不支持的静态存储属性”。

我需要单例 class，所以我可以将 .dropObjectOutside viewmodifier 放在我的视图层次结构中的任何位置，所以我尝试将 ID 向下转换为字符串，但我似乎做不到那行得通。

有没有办法向下转换或使此代码接受任何对象？

import SwiftUI

// I want this to be any object
struct StopContent: Identifiable {
    var id: String = UUID().uuidString
}

// Singleton class to hold drag state
class DragToReorderController: ObservableObject {

    // Make it a singleton, so it can be accessed from any view
    static let shared = DragToReorderController()
    private init() { }

    @Published var draggedID: String? // How do I make this a T.ID or downcast T.ID to string everywhere else?
    @Published var dragActive:Bool = false

}


// Add ViewModifier to view
extension View {

    func dragToReorder(_ item: StopContent, array: Binding<[StopContent]>) -> some View {
        self.modifier(DragToReorderObject(sourceItem: item, contentArray: array))
    }

    func dropOutside() -> some View {
        self.onDrop(of: [UTType.text], delegate: DropObjectOutsideDelegate())
    }
}


import UniformTypeIdentifiers

// MARK: View Modifier
struct DragToReorderObject: ViewModifier {

    let sourceItem: StopContent
    @Binding var contentArray: [StopContent]

    @ObservedObject private var dragReorder = DragToReorderController.shared

    func body(content: Content) -> some View {
        content
        .onDrag {
            dragReorder.draggedID = sourceItem.id
            dragReorder.dragActive = false
            return NSItemProvider(object: String(sourceItem.id) as NSString)
        }
        .onDrop(of: [UTType.text], delegate: DropObjectDelegate(sourceItem: sourceItem, listData: $contentArray, draggedItem: $dragReorder.draggedID, dragActive: $dragReorder.dragActive))
        .onChange(of: dragReorder.dragActive, perform: { value in
            if value == false {
                // Drag completed
            }
        })
        .opacity(dragReorder.draggedID == sourceItem.id && dragReorder.dragActive ? 0 : 1)
            
    }
}

// MARK: Drop and reorder
struct DropObjectDelegate: DropDelegate {

    let sourceItem: StopContent
    @Binding var listData: [StopContent]
    @Binding var draggedItem: String?
    @Binding var dragActive: Bool


    func dropEntered(info: DropInfo) {
    
        if draggedItem == nil { draggedItem = sourceItem.id }
    
        dragActive = true
    
        // Make sure the dragged item has moved and that it still exists
        if sourceItem.id != draggedItem {
            if let draggedItemValid = draggedItem {
                if let from = listData.firstIndex(where: { [=10=].id == draggedItemValid } ) {
                
                    // If that is true, move it to the new location
                    let to = listData.firstIndex(where: { [=10=].id == sourceItem.id } )!
                
                    if listData[to].id != draggedItem! {
                        listData.move(fromOffsets: IndexSet(integer: from),
                            toOffset: to > from ? to + 1 : to)
                    }
                }
            }
        }
    }

    func dropUpdated(info: DropInfo) -> DropProposal? {
        return DropProposal(operation: .move)
    }

    func performDrop(info: DropInfo) -> Bool {
        dragActive = false
        draggedItem = nil
        return true
    }

}


// MARK: Drop and cancel
struct DropObjectOutsideDelegate: DropDelegate {

    // Using a singleton so we can drop anywhere
    @ObservedObject private var dragReorder = DragToReorderController.shared
    
    func dropEntered(info: DropInfo) {
        dragReorder.dragActive = true
    }

    func performDrop(info: DropInfo) -> Bool {
        dragReorder.dragActive = false
        dragReorder.draggedID = nil
        return true
    }
}

Answer 1

为此，您必须在所有地方添加 Identifiable 通用约束。此外，将 Int 用于 draggedID 而不是 String.

这是演示代码。

// Singleton class to hold drag state
class DragToReorderController: ObservableObject {

    // Make it a singleton, so it can be accessed from any view
    static let shared = DragToReorderController()
    private init() { }

    @Published var draggedID: Int?
    @Published var dragActive: Bool = false
}


// Add ViewModifier to view
extension View {

    func dragToReorder<T: Identifiable>(_ item: T, array: Binding<[T]>) -> some View {
        self.modifier(DragToReorderObject(sourceItem: item, contentArray: array))
    }

    func dropOutside() -> some View {
        self.onDrop(of: [UTType.text], delegate: DropObjectOutsideDelegate())
    }
}


import UniformTypeIdentifiers

// MARK: View Modifier
struct DragToReorderObject<T: Identifiable>: ViewModifier {
    
    let sourceItem: T
    @Binding var contentArray: [T]
    
    @ObservedObject private var dragReorder = DragToReorderController.shared
    
    func body(content: Content) -> some View {
        content
            .onDrag {
                dragReorder.draggedID = sourceItem.id.hashValue
                dragReorder.dragActive = false
                return NSItemProvider(object: String(sourceItem.id.hashValue) as NSString)
            }
            .onDrop(of: [UTType.text], delegate: DropObjectDelegate(sourceItem: sourceItem, listData: $contentArray, draggedItem: $dragReorder.draggedID, dragActive: $dragReorder.dragActive))
            .onChange(of: dragReorder.dragActive, perform: { value in
                if value == false {
                    // Drag completed
                }
            })
            .opacity((dragReorder.draggedID == sourceItem.id.hashValue) && dragReorder.dragActive ? 0 : 1)
    }
}

// MARK: Drop and reorder
struct DropObjectDelegate<T: Identifiable>: DropDelegate {

    let sourceItem: T
    @Binding var listData: [T]
    @Binding var draggedItem: Int?
    @Binding var dragActive: Bool


    func dropEntered(info: DropInfo) {
    
        if draggedItem == nil { draggedItem = sourceItem.id.hashValue }
    
        dragActive = true
    
        // Make sure the dragged item has moved and that it still exists
        if sourceItem.id.hashValue != draggedItem {
            if let draggedItemValid = draggedItem {
                if let from = listData.firstIndex(where: { [=10=].id.hashValue == draggedItemValid } ) {
                
                    // If that is true, move it to the new location
                    let to = listData.firstIndex(where: { [=10=].id == sourceItem.id } )!
                
                    if listData[to].id.hashValue != draggedItem! {
                        listData.move(fromOffsets: IndexSet(integer: from),
                            toOffset: to > from ? to + 1 : to)
                    }
                }
            }
        }
    }

    func dropUpdated(info: DropInfo) -> DropProposal? {
        return DropProposal(operation: .move)
    }

    func performDrop(info: DropInfo) -> Bool {
        dragActive = false
        draggedItem = nil
        return true
    }

}


// MARK: Drop and cancel
struct DropObjectOutsideDelegate: DropDelegate {

    // Using a singleton so we can drop anywhere
    @ObservedObject private var dragReorder = DragToReorderController.shared
    
    func dropEntered(info: DropInfo) {
        dragReorder.dragActive = true
    }

    func performDrop(info: DropInfo) -> Bool {
        dragReorder.dragActive = false
        dragReorder.draggedID = nil
        return true
    }
}

如何使拖放视图修改器接受任何对象

How to make a drag and drop viewmodifier accept any object

drag-and-drop

downcast

swiftui