SwiftUI View and @FetchRequest predicate with variable that can change

Question

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

struct ChatView: View {

@FetchRequest(         


        

Answer 1

May be a more general solution for dynamically filtering @FetchRequest.

1、Create custom DynamicFetchView

import CoreData
import SwiftUI

struct DynamicFetchView: View {
    let fetchRequest: FetchRequest
    let content: (FetchedResults) -> Content

    var body: some View {
        self.content(fetchRequest.wrappedValue)
    }

    init(predicate: NSPredicate?, sortDescriptors: [NSSortDescriptor], @ViewBuilder content: @escaping (FetchedResults) -> Content) {
        fetchRequest = FetchRequest(entity: T.entity(), sortDescriptors: sortDescriptors, predicate: predicate)
        self.content = content
    }

    init(fetchRequest: NSFetchRequest, @ViewBuilder content: @escaping (FetchedResults) -> Content) {
        self.fetchRequest = FetchRequest(fetchRequest: fetchRequest)
        self.content = content
    }
}

2、how to use

//our managed object
public class Event: NSManagedObject{
    @NSManaged public var status: String?
    @NSManaged public var createTime: Date?
    ... ...
}

// some view

struct DynamicFetchViewExample: View {
    @State var status: String = "undo"

    var body: some View {
        VStack {
            Button(action: {
                self.status = self.status == "done" ? "undo" : "done"
            }) {
                Text("change status")
                    .padding()
            }

            // use like this
            DynamicFetchView(predicate: NSPredicate(format: "status==%@", self.status as String), sortDescriptors: [NSSortDescriptor(key: "createTime", ascending: true)]) { (events: FetchedResults) in
                // use you wanted result
                // ...
                HStack {
                    Text(String(events.count))
                    ForEach(events, id: \.self) { event in
                        Text(event.name ?? "")
                    }
                }
            }

            // or this
            DynamicFetchView(fetchRequest: createRequest(status: self.status)) { (events: FetchedResults) in
                // use you wanted result
                // ...
                HStack {
                    Text(String(events.count))
                    ForEach(events, id: \.self) { event in
                        Text(event.name ?? "")
                    }
                }
            }
        }
    }

    func createRequest(status: String) -> NSFetchRequest {
        let request = Event.fetchRequest() as! NSFetchRequest
        request.predicate = NSPredicate(format: "status==%@", status as String)
        // warning: FetchRequest must have a sort descriptor
        request.sortDescriptors = [NSSortDescriptor(key: "createTime", ascending: true)]
        return request
    }
}

In this way, you can dynamic change your NSPredicate or NSSortDescriptor.