SwiftUI2.0添加新子項時如何及時重繪串列？

大家都知道，從 SwiftUI 2.0 開始，List 就支持了遞回資料的分層展示。

我的遞回資料結構樹定義如下：

class Tree<Value: Hashable>: Hashable {
    static func == (lhs: Tree<Value>, rhs: Tree<Value>) -> Bool {
        lhs.value == rhs.value
    }
    
    func hash(into hasher: inout Hasher) {
        hasher.combine(value)
    }
    
    let value: Value
    var children: [Tree]? = nil
    
    init(value: Value, children: [Tree]? = nil){
        self.value = value
        self.children = children
    }
}

我的模型定義如下：

class Model: ObservableObject {
    @Published var trees = [Tree<String>]()
}

最后是我的 TreeView 定義：

struct TreeView: View {
    
    @StateObject var model = Model()
    
    var body: some View {
        VStack {
            HStack {
                Spacer()
                Button(" "){
                    let new = Tree(value: String(UUID().uuidString.prefix(16)))
                    // List can be refreshed in time
                    model.trees.append(new)
                }
            }
            .padding()
            
            Text("Tree")
                .font(.title)
            
            Spacer()
            
            List {
                ForEach(model.trees, id: \.value){ section in
                    Section(header: HStack {
                        Text("\(section.value)")
                        Spacer()
                        Button(" "){
                            let new = Tree(value: String(UUID().uuidString.prefix(8)))
                            var new_children: [Tree<String>]
                            if let children = section.children {
                                new_children = children
                                new_children.append(new)
                            }else{
                                new_children = [new]
                            }
                            
                            // List can't be refreshed in time
                            section.children = new_children
                        }
                        .buttonStyle(BorderlessButtonStyle())
                    }){
                        OutlineGroup(section.children ?? [], id: \.value, children: \.children){tree in
                            HStack {
                                Text(tree.value)
                                Spacer()
                                Button(" "){
                                    let new = Tree(value: String(UUID().uuidString.prefix(8)))
                                    var new_children: [Tree<String>]
                                    if let children = tree.children {
                                        new_children = children
                                        new_children.append(new)
                                    }else{
                                        new_children = [new]
                                    }
                                    // List can't be refreshed in time
                                    tree.children = new_children
                                }
                                .buttonStyle(BorderlessButtonStyle())
                            }
                        }
                    }
                }
            }
            .listStyle(SidebarListStyle())
        }
    }
}

struct ProductListView_Previews: PreviewProvider {
    static var previews: some View {
        TreeView()
    }
}

當我在model.trees陣列中添加新Tree時，List可以及時重繪 ，但是當我給trees陣列中的一個元素添加新Tree時（例如：model.trees[0]），List就不能神清氣爽。

添加子樹時如何及時重繪 串列？謝謝！

uj5u.com熱心網友回復：

作為每個“ ”按鈕插入的第一個命令：
model.objectWillChange.send()- 然后它作業。

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