无法将 'Binding<String?>' 类型的值转换为预期的参数类型 'Binding<String>'

Question

我试图在一个单独的详细信息视图中编辑一个项目。我想在从列表中选择项目后，在文本字段中填充项目详细信息。

List {
ForEach(vm.savedEntites) { entity in
Text(entity.name ?? "No Name")
HStack {
Button(action: {vm.deleteMemory(entity: entity)}) {
Label("Delete",systemImage: "trash")

}

Button(action: {
vm.selectedEntity = entity
showingDetailScreen.toggle()}) {
Label("Details", systemImage: "pencil")
}

}
}// list ends here
.sheet(isPresented: $showingDetailScreen) {
DetailItemView(isVisible: self.$showingDetailScreen, entity: vm.selectedEntity!, text: vm.selectedEntity!)
}// sheet ends here
}

详细项视图表。这就是我得到这个错误旁边的TextField

无法将类型"Binding<String?>"的值转换为期望的参数类型"绑定">

struct DetailItemView: View  {

@Environment(.presentationMode) var presentationMode
@Binding var isVisible: Bool
var entity: MemoryEntity
@ObservedObject var text: MemoryEntity

var body: some View {
Text(entity.name ?? "No Name")
TextField(text.name ?? "No Name", text: $text.name)
....}

这是项

的CoreData模型类

class CoreDataViewModel: ObservableObject {
let container: NSPersistentContainer
@Published var savedEntites: [MemoryEntity] = []
@Published var selectedEntity: MemoryEntity?
init() {
container = NSPersistentContainer(name: "MemoryContainer")
container.loadPersistentStores { (description, error) in
if let error = error {
print("Error loading CoreData. (error)")
}
}
FetchMemories()
}

Answer 1

因为所有核心数据字段都是可选的，所以必须将其封装到Binding中。当你使用核心数据，可能面临很多可选的，你可以创建一个扩展:

extension Binding {
func toUnwrapped<T>(defaultValue: T) -> Binding<T> where Value == Optional<T>  {
Binding<T>(get: { self.wrappedValue ?? defaultValue }, set: { self.wrappedValue = $0 })
}
}

像这样使用:

TextField("title", text: $text.name.toUnwrapped(defaultValue: ""))