這節主要演示瞭如何通過新增第二個螢幕來跟蹤應用程式的call歷史來擴充套件Phoneword應用程式。最終如下:

　　按如下步驟擴充套件Phoneword

　　在Phoneword專案右鍵新建Content Page,命名為CallHistoryPage

 　　修改後CallHistoryPage.xaml如下：

<?xml version="1.0" encoding="UTF-8"?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
                   xmlns:local
 
="clr-namespace:Phoneword;assembly=Phoneword"
                   xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
                   x:Class="Phoneword.CallHistoryPage"
                   Title="Call History">
    <ContentPage.Padding>
        <OnPlatform x:TypeArguments="Thickness">
            <
 
On Platform="iOS" Value="20, 40, 20, 20" />
            <On Platform="Android, UWP" Value="20" />
        </OnPlatform>
    </ContentPage.Padding>
    <StackLayout>
      <ListView ItemsSource="{x:Static local:App.PhoneNumbers}" />
    </StackLayout>
</ContentPage>

　　雙擊

　　新增PhoneNumbers屬性的宣告，在App建構函式中初始化該屬性，並將MainPage屬性初始化為NavigationPage。PhoneNumbers被用於儲存應用程式打的每個電話號碼

using System.Collections.Generic;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;

[assembly: XamlCompilation(XamlCompilationOptions.Compile)]
namespace Phoneword
{
    public partial class App : Application
    {
        public static IList<string> PhoneNumbers { get; set; }

        public App()
        {
            InitializeComponent();
            PhoneNumbers = new List<string>();
            MainPage = new NavigationPage(new MainPage());
        }
        ...
    }
}

　　雙擊Phoneword專案的MainPage.xaml檔案

　　在StackLayout控制元件的末尾新增一個按鈕控制元件，該按鈕被用於導航到撥打歷史頁面

<StackLayout VerticalOptions="FillAndExpand"
             HorizontalOptions="FillAndExpand"
             Orientation="Vertical"
             Spacing="15">
  ...
<Button x:Name="callButton" Text="Call" IsEnabled="false" Clicked="OnCall" />
  <Button x:Name="callHistoryButton" Text="Call History" IsEnabled="false"
          Clicked="OnCallHistory" />
</StackLayout>

　　開啟隱藏檔案MainPage.xaml.cs，新增OnCallHistory事件處理程式方法，並修改OnCall事件處理程式方法，將轉換後的電話號碼新增到App.PhoneNumbers集合中，並且如果dialer變數不為null時使能callHistoryButton

using System;
using Xamarin.Forms;

namespace Phoneword
{
    public partial class MainPage : ContentPage
    {
        ...

        async void OnCall(object sender, EventArgs e)
        {
            ...
            if (dialer != null) {
                App.PhoneNumbers.Add (translatedNumber);
                callHistoryButton.IsEnabled = true;
                dialer.Dial (translatedNumber);
            }
            ...
        }

        async void OnCallHistory(object sender, EventArgs e)
        {
            await Navigation.PushAsync (new CallHistoryPage ());
        }
    }
}

　　下節剖析該擴充套件