无法推断复杂的闭包返回类型 SwiftUI ForEach

Posted 2023-02-24

【中文标题】无法推断复杂的闭包返回类型 SwiftUI ForEach

【英文标题】：Unable to infer complex closure return type SwiftUI ForEach

【发布时间】：2020-01-08 12:04:00

【问题描述】：

我正在尝试显示过滤后的 List，其中仅包含与 self.day[index] 完全匹配的 subjects。但是，当我尝试为此使用if 子句时，我收到错误Unable to infer complex closure return type; add explicit type to disambiguate。有人可以找到任何其他方法将subject 过滤为subject.day 以等于self.days[index] 吗？这是我的代码，谢谢：

import SwiftUI
import CoreData

struct ProfileView: View 
    @Environment(\.managedObjectContext) var moc: NSManagedObjectContext
    @FetchRequest(
        entity: Subject.entity(),
        sortDescriptors:[
        //NSSortDescriptor(keyPath: \Subject.day, ascending: true),
        NSSortDescriptor(keyPath: \Subject.start, ascending: true)
        ]
    ) var subjects: FetchedResults<Subject>

    @State private var showAddScreen = false
    @State private var name: String = ""
    @State private var surname: String = ""
    let days = ["Pondelok", "Utorok", "Streda", "Štvrtok", "Piatok"]

    var body: some View 
        Form 
            ForEach(0 ..< days.count)  index in
                Section 
                    Text(self.days[index])
                    List 
                        ForEach(self.subjects, id: \.self)  subject in //here the  shows an error, If I remove the if clause, it works, but obviously I don't have subjects filltered, which is what I need
                            if subject.day == self.days[index] 
                            SubjectCell(name: "\(subject.name!)",
                                place: "\(subject.place!)",
                                start: self.formatTime(date: subject.start ?? Date()),
                                end: self.formatTime(date: subject.end ?? Date()),
                                type: subject.type,
                                occurance: subject.occurance)
                            
                        
                        .onDelete(perform: self.deleteSubject)

【参考方案1】：

将整个if .. 包装成Group .. 解决了问题

【参考方案2】：

根据相同的标准过滤掉主题，然后返回它们的列表不是更好吗？有机会在FetchRequest 或List 内部进行，然后使用return ForEach(filteredSubjects, id: \.self) ...。