SwiftUI View和@FetchRequest谓词具有可以更改的变量 [英] SwiftUI View and @FetchRequest predicate with variable that can change

问题描述

我有一个视图，显示团队中使用@Fetchrequest和固定谓词开发人员过滤的消息。

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)
                }
            }...

我想使此谓词动态化，以便在用户切换团队时显示该团队的消息。下面的代码给我以下错误

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

无法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自我可用之前运行

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

...

我可以为此提供一些帮助，但到目前为止我还无法自行解决。

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

推荐答案

遇到了同样的问题，布拉德·狄龙（Brad Dillon）的评论显示了解决方案：

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))

    }

在此示例中，您可以在初始化程序中修改谓词。

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

这篇关于SwiftUI View和@FetchRequest谓词具有可以更改的变量的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！