Kia ora koutou!

I've been working on showing some CoreData using a UICalendarView, but am having trouble getting my data model which is an @ObservedObject to update the decorations on the calendar. My file looks like this:

//
//  CalendarView.swift
//  mInr
//
//  Created by Finn LeSueur on 2/03/23.
//

import SwiftUI

struct CalendarView: UIViewRepresentable {
    let interval: DateInterval
    @ObservedObject var dataModel = DataManager.shared
    @AppStorage("lightAccentColour") var lightAccentColour: Color = .red
    @AppStorage("darkAccentColour") var darkAccentColour: Color = .yellow

    func makeUIView(context: Context) -> UICalendarView {
        let view = UICalendarView()
        view.delegate = context.coordinator
        view.availableDateRange = interval
        view.setContentCompressionResistancePriority(.defaultLow, for: .vertical)
        view.setContentCompressionResistancePriority(.defaultLow, for: .horizontal)
        return view
    }

    func makeCoordinator() -> Coordinator {
        Coordinator(parent: self)
    }

    func updateUIView(_ uiView: UICalendarView, context: Context) {
        print("updateUIView called")
        context.coordinator.antiCoagulantDoses = dataModel.antiCoagulantDoses
    }

    class Coordinator: NSObject, UICalendarViewDelegate, UICalendarSelectionSingleDateDelegate {
        var parent: CalendarView
        var antiCoagulantDoses: [AntiCoagulantDose]

        init(parent: CalendarView) {
            self.parent = parent
            self.antiCoagulantDoses = self.parent.dataModel.antiCoagulantDoses
        }

        func calendarView(_ calendarView: UICalendarView, decorationFor dateComponents: DateComponents) -> UICalendarView.Decoration? {
            print("Running calendarView")
            // Don't decorate future dates.
            if dateComponents.date?.timeIntervalSinceNow.sign == FloatingPointSign.plus {
                return nil
            }

            let antiCoagulantDose = antiCoagulantDoses.first(where: { $0.timestamp?.startOfDay == dateComponents.date?.startOfDay })

            let font = UIFont.systemFont(ofSize: 12)
            let configuration = UIImage.SymbolConfiguration(font: font)

            if antiCoagulantDose == nil {
                let image = UIImage(systemName: "exclamationmark.triangle", withConfiguration: configuration)?
                    .withRenderingMode(.alwaysOriginal)
                    .withTintColor(.red)

                return .image(image)
            }

            return .customView {
                let label = UILabel()
                label.text = "\(antiCoagulantDose!.dose)g"
                label.font = UIFont.systemFont(ofSize: UIFont.smallSystemFontSize)
                return label
            }
        }

        func dateSelection(_ selection: UICalendarSelectionSingleDate,
                           didSelectDate dateComponents: DateComponents?) {
        }

        func dateSelection(_ selection: UICalendarSelectionSingleDate,
                           canSelectDate dateComponents: DateComponents?) -> Bool {
            return true
        }
    }
}

I've done a lot of searching about this, and I haven't made much progress. The @ObservedObject is working excellently for my other views (adding/deleting/updating/viewing/rendering a chart) – it's just this one!

I've set it up that I pass in the relevant data and update the coordinator with fresh data when changes occur. I can definitely see changes occuring in my logs:

Updating anticoagulant doses.
Updating anticoagulant doses.
Start: 2022-12-20 08:48:27 +0000. End: 2023-03-31 08:48:27 +0000
Start: 2022-12-20 08:48:27 +0000. End: 2023-03-31 08:48:27 +0000
updateUIView called
updateUIView called

But it seems like calendarView never gets called again – which is odd. If I change the rotation of the device or scroll back many months then it refreshes the decorations, but I can't seem to make it go manually.

Any advice would be much appreciated!

Hi, I think you need to update the decorations in updateUIView with:

uiView.reloadDecorations(forDateComponents: "Your date components", animated: true)

Display decorations for specific dates

Thanks for the reply @Hectorcrdna! I had seen that method around but was not sure how to determine what my date components should be to update. I suppose I could use .era but that would be computationally wasteful and slower than updating just a single date.

Maybe I could see if I could get my dataModel to send the most recent update? Not sure yet.

I am late to the party. I met the same issue and here's my workaround. I don't know if it's a standard way or a hack.

You could define a reference to the view you made inside the makeUIView

struct CalendarView:UIViewRepresentable{

@State var calendarView:UICalendarView?

func makeUIView(context: Context) -> UICalendarView {
         DispatchQueue.main.asyncAfter(deadline: .now()){
         self.calendarView = view
         }

}
}

And then you could use

self.calendarView?.reloadDecorations(forDateComponents: dates, animated: true)

when you need to refresh the calendar view.