C# - Xamarin - インタフェースと抽象クラス - クラスに約束を守らせる(多相性、アップキャスト、ダウンキャスト、is演算子、as演算子、参照、CombBoxの代替(Pickr)、TextBoxの代替(Editor))

Head First C#
原著

開発環境

• OS: Windows 10 Pro
• IDE(統合開発環境): Visual Studio Community 2017

Head First C# ―頭とからだで覚えるC#の基本 (Andrew Stellman (著)、Jennifer Greene (著)、佐藤 嘉一 (監修, 監修)、木下 哲也 (翻訳)、オライリージャパン)の6章(インタフェースと抽象クラス - クラスに約束を守らせる)、長いエクササイズ(p. 260)を取り組んでみる。

コード

MainPage.xaml

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:App2"
             x:Class="App2.MainPage">

    <StackLayout>
        <Editor x:Name="description"/>
        <Button x:Name="goHere"
                Text="ここへ行け"
                Clicked="goHere_Clicked"/>
        <Picker x:Name="exits"/>
        <Button x:Name="goThroughTheDoor"
                Text="このドアを使え。"
                Clicked="goThroughTheDoor_Clicked"/>
    </StackLayout>

</ContentPage>

MainPage.xaml.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Xamarin.Forms;

namespace App2
{
    public partial class MainPage : ContentPage
    {
        OutsideWithDoor frontYard;
        OutsideWithDoor backYard;
        Outside garden;
        RoomWithDoor livingRoom;
        Room diningRoom;
        RoomWithDoor kitchen;
        Location currentLocation;

        public MainPage()
        {
            InitializeComponent();

            CreateObjects();
            MoveToANewLocation(livingRoom);
        }

        private void CreateObjects()
        {
            frontYard = new OutsideWithDoor(
                "前庭",
                false,
                "真ちゅうのノブを持つオーク材のドア");
            backYard = new OutsideWithDoor(
                "裏庭",
                true,
                "網戸");
            garden = new Outside("庭園", false);
            livingRoom = new RoomWithDoor(
                "リビングルーム",
                "アンティークカーペット",
                "真ちゅうのノブを持つオーク材のドア");
            diningRoom = new Room(
                "ダイニングルーム",
                "クリスタルのシャンデリア");
            kitchen = new RoomWithDoor(
                "台所",
                "ステンレス製の電化製品",
                "網戸");

            frontYard.exists = new Location[] { livingRoom, garden};
            backYard.exists = new Location[] { diningRoom, garden };
            garden.exists = new Location[] { frontYard, backYard };
            livingRoom.exists = new Location[] { frontYard, diningRoom };
            diningRoom.exists = new Location[] { livingRoom, kitchen };
            kitchen.exists = new Location[] { diningRoom, backYard };

            frontYard.DoorLocation = livingRoom;
            backYard.DoorLocation = kitchen;
            livingRoom.DoorLocation = frontYard;
            kitchen.DoorLocation = backYard;
        }

        private void MoveToANewLocation(Location location)
        {
            currentLocation = location;
            exits.Items.Clear();
            foreach (var item in currentLocation.exists)
            {
                exits.Items.Add(item.Name);
            }
            exits.SelectedIndex = 0;
            description.Text = currentLocation.Description;
            goThroughTheDoor.IsVisible = 
                currentLocation is IHasExteriorDoor ? true : false;
        }

        private void goHere_Clicked(object sender, EventArgs e)
        {
            MoveToANewLocation(currentLocation.exists[exits.SelectedIndex]);
        }

        private void goThroughTheDoor_Clicked(object sender, EventArgs e)
        {
            IHasExteriorDoor hasExteriorDoor = 
                currentLocation as IHasExteriorDoor;
            MoveToANewLocation(hasExteriorDoor.DoorLocation);
        }
    }
    public interface IHasExteriorDoor
    {
        string DoorDescription { get; }
        Location DoorLocation { get; }
    }
    public class Room: Location
    {
        private string decoration;

        public Room(string name, string decoration):
            base(name)
        {
            this.decoration = decoration;
        }

        public string Decoration => decoration;
    }
    public class Outside: Location
    {
        private bool hot;

        public Outside(string name, bool hot):
            base(name)
        {
            this.hot = hot;
        }

        public bool Hot => hot;
        public override string Description
        {
            get
            {
                string description = base.Description;
                if (hot)
                {
                    description += "ここはとても暑い。";
                }
                return description;
            }
        }
    }
    public class OutsideWithDoor: Outside, IHasExteriorDoor
    {
        private Location location;
        private string doorDescription;

        public OutsideWithDoor(
            string name, bool hot, string doorDescription)
            :base(name, hot)
        {
            this.doorDescription = doorDescription;
        }
        
        public string DoorDescription => doorDescription;

        public Location DoorLocation
        {
            get => location;
            set => location = value;
        }
    }
    public class RoomWithDoor : Room, IHasExteriorDoor
    {
        private string doorDescription;
        private Location location;

        public RoomWithDoor(
            string name, string decoration, string doorDescription)
            : base(name, decoration)
        {
            this.doorDescription = doorDescription;
        }

        public string DoorDescription => doorDescription;
        public Location DoorLocation
        {
            get => location;
            set => location = value;
        }
    }
}

App.xaml

<?xml version="1.0" encoding="utf-8" ?>
<Application xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="App2.App">
 <Application.Resources>
    
 </Application.Resources>
</Application>

App.xaml.cs

using System;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;

[assembly: XamlCompilation (XamlCompilationOptions.Compile)]
namespace App2
{
 public partial class App : Application
 {
  public App ()
  {
   InitializeComponent();

            // MainPage = new MainPage();
            MainPage = 
                new NavigationPage(
                    new MainPage() { Title = "家の探索" });
  }

  protected override void OnStart ()
  {
   // Handle when your app starts
  }

  protected override void OnSleep ()
  {
   // Handle when your app sleeps
  }

  protected override void OnResume ()
  {
   // Handle when your app resumes
  }
 }
}