Not sure why whenever i want to increment the completion count in the detailed view, it increments in the detailed view but when i go back to the previous content view page and click into the detailed view, the count resets to 0. is there a way for me to rectify this?

ContentView.swift

//
//  ContentView.swift
//  Habit Tracker
//
//  Created by YeetdSkra on 2/3/21.
//

import SwiftUI

struct Activity: Identifiable, Codable {
    var id = UUID()
    let Title : String
    let ActivityType : String
    let Description : String
    var Count : Int

    public mutating func incrementAmount() {
        self.Count += 1
    }
}

class ActivityArray: ObservableObject {
    // Array to hold activities and stores them into UserDefaults
    @Published var items = [Activity]() {
        // Save changes, when activity is added or deleted
        didSet {
            let encoder = JSONEncoder()
            // Encodes activities and stores it into the UserDefaults
            if let encoded = try? encoder.encode(items) {
                UserDefaults.standard.set(encoded, forKey: "Items")
            }
        }
    }

    // Automatically loads data from UserDefaults
    init() {
        if let items = UserDefaults.standard.data(forKey: "Items") {
            let decoder = JSONDecoder()
            // Decode data from UserDefaults
            if let decoded = try? decoder.decode([Activity].self, from: items) {
                self.items = decoded
                return
            }
        }
        // if decoding didnt go through, activity array will be empty
        self.items = []
    }
}

struct ContentView: View {
    @ObservedObject var activities = ActivityArray()
    @State private var showingAddActivity = false

    var body: some View {
        NavigationView {
            List {
                ForEach(activities.items) { item in
                    NavigationLink(destination: HabitView(activity: item)) {
                    HStack {
                        VStack(alignment: .leading) {
                            Text(item.Title)
                                .font(.headline)
                            Text(item.ActivityType)
                        }
                    }
                        Spacer()
                    }
                }
                .onDelete(perform: removeItems)
            }
            .navigationBarTitle("Habitual")
            .navigationBarItems(trailing:
                Button(action: {
                    self.showingAddActivity = true
                }) {
                    Image(systemName: "plus")
                }
            )
            .sheet(isPresented: $showingAddActivity) {
                addActivityView(activities: self.activities)
            }
        }
    }

    func removeItems(at offsets: IndexSet) {
        activities.items.remove(atOffsets: offsets)
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        Group {
            ContentView()
            ContentView()
        }
    }
}

HabitView.swift

//  Created by YeetdSkra on 4/3/21.
//
// Detailed View of the Habit

import Foundation
import SwiftUI

struct HabitView: View {
    @State var activity: Activity

    var body: some View {
        VStack {
            Text(activity.Title)
            Text(activity.ActivityType)
            Text(activity.Description)
            Text("Completion Count:\(activity.Count)")
            Spacer()
            Button("Increment completion count by 1") {
                activity.incrementAmount()
            }
        }
    }
}

struct HabitView_Previews: PreviewProvider {
    static var previews: some View {
        HabitView(activity: ActivityArray().items[0])
    }
}

AddActivityView.swift

//
//  AddActivityView.swift
//  Habit Tracker
//
//  Created by YeetdSkra on 4/3/21.
//

import Foundation
import SwiftUI

struct addActivityView: View {
    @ObservedObject var activities: ActivityArray
    @State private var Title = ""
    @State private var type = "Routine"
    @State private var Description = ""
    @State private var Count = 0
    @Environment(\.presentationMode) var presentationMode

    static let types = ["Work","Hygiene"]

    var body: some View {
        NavigationView {
            Form {
                TextField("Activity Title", text: $Title)
                Picker("Type", selection: $type) {
                    ForEach(Self.types, id: \.self) {
                        Text($0)
                    }
                }
                TextField("Description of activity", text: $Description)
            }
            .navigationBarTitle("Add a new activity")
            .navigationBarItems(trailing: Button("Save") {
                let item = Activity(Title: self.Title, ActivityType: self.type, Description: self.Description, Count: self.Count)
                self.activities.items.append(item)
                self.presentationMode.wrappedValue.dismiss()
            })
        }
    }
}

struct AddView_Previews: PreviewProvider {
    static var previews: some View {
        addActivityView(activities: ActivityArray())
    }
}