可选的@State 变量未初始化

Question

我希望能够打开一个工作表视图，用户在其中点击列表上的某些内容，并且来自该点击的列表单元格的所有信息都显示在工作表视图上。 但是，我很难尝试将可选的 @State 变量初始化为列表值。 这是我得到的错误：

Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value

State 变量似乎保持为空，因此代码回复它的原因是它得到一个 nil 值。 我怎样才能得到一个实际值在里面所以它不是零？

任何帮助，将不胜感激。

我的代码如下：

struct ContentView: View {
    
    @Environment(\.managedObjectContext) var managedObjContext
    @FetchRequest(sortDescriptors: [SortDescriptor(\.date, order: .reverse)]) var counters: FetchedResults<Counter>
    
    @State private var creatingCounter = false
    @State private var editingCounter = false
    @State private var selectedCounter: FetchedResults<Counter>.Element? // The optional State var.
    
    var body: some View {
        NavigationView {
            VStack {
                List {
                    ForEach(counters) { counter in
                        TimelineView(.periodic(from: .now, by: 1.0)) { timeline in
                            CounterCellView(title: counter.title ?? "", icon: counter.icon ?? "", color: counter.color ?? "", date: counter.date ?? Date())
                        }
                        .listRowSeparator(.hidden)
                        .onTapGesture {
                            selectedCounter = counter // I want the state var to be initialized to the tapped item on the list.
                            editingCounter.toggle()
                        }
                    }
                    .onDelete(perform: deleteCounter)
                    
                }
                .listStyle(.inset)
            }
            .navigationTitle("Counters")
            .navigationBarTitleDisplayMode(.inline)
            .toolbar {
                ToolbarItem(placement: .navigationBarTrailing) {
                    Button {
                        creatingCounter.toggle()
                    } label: {
                        Image(systemName: "plus")
                    }
                }
            }
        }
        .sheet(isPresented: $creatingCounter) {
            CreateCounterView(creatingCounter: $creatingCounter)
        }
        .sheet(isPresented: $editingCounter) {
            EditCounterView(editingCounter: $editingCounter, counter: selectedCounter!) // Where I am getting the error.
        }
    }
    
    func deleteCounter(at offsets: IndexSet) {
        
        withAnimation {
            offsets.map { counters[$0] }.forEach(managedObjContext.delete)
            DataController().save(context: managedObjContext)
        }
    }
}

Answer 1

试试这个方法：

删除所有editingCounter并使用类似.sheet(item: $selectedCounter)的东西，而不是你的.sheet(isPresented: $editingCounter) ：

.sheet(item: $selectedCounter) { kounter in    // <-- here
    if let theCounter = kounter {
        //-- here, adjust the EditCounterView (ie remove the editingCounter)
        EditCounterView(counter: theCounter)  
    }
}
    

如果需要，您可能必须声明@State private var selectedCounter: Counter?