SwiftUI 视图和带有可以更改的变量的 @FetchRequest 谓词 [英] SwiftUI View and @FetchRequest predicate with variable that can change

问题描述

我有一个视图显示团队中的消息，这些消息使用带有固定谓词开发人员"的@Fetchrequest 进行过滤.

I have a view showing messages in a team that are filtered using @Fetchrequest with a fixed predicate 'Developers'.

struct ChatView: View {

@FetchRequest(
    sortDescriptors: [NSSortDescriptor(keyPath: Message.createdAt, ascending: true)],
    predicate: NSPredicate(format: "team.name == %@", "Developers"),
    animation: .default) var messages: FetchedResults<Message>

@Environment(.managedObjectContext)
var viewContext

var body: some View {
    VStack {
        List {
            ForEach(messages, id: .self) { message in
                VStack(alignment: .leading, spacing: 0) {
                    Text(message.text ?? "Message text Error")
                    Text("Team (message.team?.name ?? "Team Name Error")").font(.footnote)
                }
            }...

我想让这个谓词动态化，这样当用户切换团队时，该团队的消息就会显示出来.下面的代码给了我以下错误

I want to make this predicate dynamic so that when the user switches team the messages of that team are shown. The code below gives me the following error

不能在属性初始值设定项中使用实例成员teamName"；属性初始值设定项在 'self' 可用之前运行

Cannot use instance member 'teamName' within property initializer; property initializers run before 'self' is available

struct ChatView: View {

@Binding var teamName: String

@FetchRequest(
    sortDescriptors: [NSSortDescriptor(keyPath: Message.createdAt, ascending: true)],
    predicate: NSPredicate(format: "team.name == %@", teamName),
    animation: .default) var messages: FetchedResults<Message>

@Environment(.managedObjectContext)
var viewContext

...

我可以使用一些帮助来解决这个问题，到目前为止我无法自己解决这个问题.

I can use some help with this, so far I'm not able to figure this out on my own.

推荐答案

有同样的问题，Brad Dillon 的评论给出了解决方案:

had the same problem, and a comment of Brad Dillon showed the solution:

var predicate:String
var wordsRequest : FetchRequest<Word>
var words : FetchedResults<Word>{wordsRequest.wrappedValue}

    init(predicate:String){
        self.predicate = predicate
        self.wordsRequest = FetchRequest(entity: Word.entity(), sortDescriptors: [], predicate:
            NSPredicate(format: "%K == %@", #keyPath(Word.character),predicate))

    }

在这个例子中，你可以修改初始化器中的谓词.

in this example, you can modify the predicate in the initializer.

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