C# - Xamarin - 継承 - オブジェクトの系図(クラス、フィールド、プロパティ、コンストラクタ)

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5章(継承 - オブジェクトの系図)、エクササイズ(p. 178)を取り組んでみる。

コード

MainPage.xaml

<?xml version="1.0" encoding="utf-8" ?>
<TabbedPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:App1"
             x:Class="App1.MainPage">
    <ContentPage Title="夕食会">
        <StackLayout>
            <Label Text="参加人数"/>
            <Slider x:Name="total1"
                    Maximum="20"
                    Value="5"/>
            <Label Text="デコレーション" />
            <Switch IsToggled="True"/>
            <Label Text="ヘルシーオプション"/>
            <Switch IsToggled="False" />
            <Label Text="総額"/>
        </StackLayout>
    </ContentPage>
    <ContentPage Title="誕生会">
        <StackLayout>
            <Label Text="参加人数"/>
            <Label x:Name="label2"
                   Text="5人"/>
            <Slider x:Name="numberBirthday" 
                    Maximum="20"
                    Value="5"
                    ValueChanged="numberBirthday_ValueChanged"/>
            <Label Text="デコレーション" />
            <Switch x:Name="fancyBirthday"
                    IsToggled="True"
                    Toggled="fancyBirthday_Toggled"/>
            <Label Text="ケーキに書き込む文字"/>
            <Editor x:Name="cakeWriting"
                    Text="Happy Birthday"
                    TextChanged="cakeWriting_TextChanged"/>
            <Label x:Name="birthdayCost"
                   Text="総額"/>
        </StackLayout>
    </ContentPage>
</TabbedPage>

MainPage.xaml.cs

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

namespace App1
{
    public partial class MainPage : TabbedPage
    {
        BirthdayParty birthdayParty;

        public MainPage()
        {
            InitializeComponent();

            birthdayParty = new BirthdayParty(
                (int)numberBirthday.Value,
                fancyBirthday.IsToggled,
                cakeWriting.Text);

            DisplayDinnerPartyCost();
        }

        private void numberBirthday_ValueChanged(object sender, ValueChangedEventArgs e)
        {
            label2.Text = numberBirthday.Value + "人";
            birthdayParty.NumberOfPeople = (int)numberBirthday.Value;
            DisplayDinnerPartyCost();
        }

        private void fancyBirthday_Toggled(object sender, ToggledEventArgs e)
        {
            birthdayParty.CalculateCostOfDecorations(fancyBirthday.IsToggled);
            DisplayDinnerPartyCost();
        }

        private void cakeWriting_TextChanged(object sender, TextChangedEventArgs e)
        {
            birthdayParty.CakeWriting = cakeWriting.Text;
            DisplayDinnerPartyCost();
        }

        private void DisplayDinnerPartyCost()
        {
            decimal cost = birthdayParty.CalculateCost(fancyBirthday.IsToggled);
            birthdayCost.Text = cost.ToString("c"); ;

        }
    }

    public class BirthdayParty: ContentPage
    {
        const int costOfFoodPerPerson = 25;
        private int numberOfPeople;
        private bool fancyDecorations;
        private decimal costOfDecorations = 0;
        private int cakeSize;
        private string cakeWriting = "";

        public BirthdayParty
            (int numberOfPeople, bool fancyDecorations, string cakeWriting)
        {
            this.numberOfPeople = numberOfPeople;
            CalculateCakeSize();
            this.fancyDecorations = fancyDecorations;
            this.cakeWriting = cakeWriting;
            CalculateCostOfDecorations(fancyDecorations);
        }

        public int NumberOfPeople
        {
            get { return numberOfPeople; }
            set
            {
                numberOfPeople = value;
                CalculateCakeSize();
                CalculateCostOfDecorations(fancyDecorations);
                this.CakeWriting = cakeWriting;
            }
        }
        public bool FancyDerocations
        {
            get { return fancyDecorations; }
            set { fancyDecorations = value; }
        }
        public string CakeWriting
        {
            get { return this.cakeWriting; }
            set
            {
                int maxLength = cakeSize == 7 ? 16 : 40;

                if (value.Length > maxLength)
                {
                    DisplayAlert(
                        "",
                        cakeSize + "号のケーキには文字が多すぎます。",
                        "OK");
                    if (maxLength > this.cakeWriting.Length)
                    {
                        maxLength = this.cakeWriting.Length;
                    }
                    this.cakeWriting = cakeWriting.Substring(0, maxLength);
                }
                else
                {
                    this.cakeWriting = value;
                }
            }
        }
        private void CalculateCakeSize()
        {
            cakeSize = numberOfPeople <= 4 ? 7 : 15;
        }
        public void CalculateCostOfDecorations(bool fancy)
        {
            fancyDecorations = fancy;
            if (fancy)
            {
                costOfDecorations = (numberOfPeople * 15.00M) + 50M;
            }
            else
            {
                costOfDecorations = (numberOfPeople * 7.50M) + 30M;
            }
        }

        public decimal CalculateCost(bool fancy)
        {
            decimal totalCost =
                costOfDecorations +
                costOfFoodPerPerson * numberOfPeople;
            decimal cakeCost =
                cakeSize == 7 ?
                400M + cakeWriting.Length * 25M :
                7500M + cakeWriting.Length * 25M;

            return totalCost + cakeCost;
        }
    }
}

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="App1.App">
    <Application.Resources>
        
    </Application.Resources>
</Application>

App.xaml.cs

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

[assembly: XamlCompilation (XamlCompilationOptions.Compile)]
namespace App1
{
 public partial class App : Application
 {
  public App ()
  {
   InitializeComponent();

            // MainPage = new MainPage();
            MainPage = new NavigationPage(
                new MainPage() { Title = "パーティーの計画" });
  }

  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
  }
 }
}