Display map from mobile map package

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// Copyright 2022 Esri
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//   https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

import ArcGIS
import SwiftUI

struct DisplayMapFromMobileMapPackageView: View {
    /// A map with no specified style.
    @State private var map = Map()

    /// The mobile map package.
    @State private var mobileMapPackage: MobileMapPackage!

    /// A Boolean value indicating whether to show an alert.
    @State private var isShowingAlert = false

    /// The error shown in the alert.
    @State private var error: Error? {
        didSet { isShowingAlert = error != nil }
    }

    /// Loads a local mobile map package.
    private func loadMobileMapPackage() async throws {
        // Loads the local mobile map package.
        let yellowstoneURL = Bundle.main.url(forResource: "Yellowstone", withExtension: "mmpk")!
        mobileMapPackage = MobileMapPackage(fileURL: yellowstoneURL)
        try await mobileMapPackage.load()
        // Gets the first map in the mobile map package.
        guard let map = mobileMapPackage.maps.first else { return }
        self.map = map
    }

    var body: some View {
        // Creates a map view to display the map.
        MapView(map: map)
            .task {
                do {
                    try await loadMobileMapPackage()
                } catch {
                    // Presents an error message if the map fails to load.
                    self.error = error
                }
            }
            .alert(isPresented: $isShowingAlert, presentingError: error)
    }
}