using System.Text;
namespace PhonewordApp
{
  public static class PhonewordTranslator
  {
    public static string ToNumber(string raw)
    {
      if (string.IsNullOrWhiteSpace(raw))
      {
        return "";
      }
      else
      {
        raw = raw.ToUpperInvariant();
      }
      var newNumber = new StringBuilder();
      foreach (var c in raw)
      {
        if ("- 0123456789".Contains(c))
          newNumber.Append(c);
        else
        {
          var result = TranslateToNumber(c);
          if (result != null)
            newNumber.Append(result);
        }
      }
      return newNumber.ToString();
    }

    static bool Contains(this string keyString, char c)
    {
      return keyString.IndexOf(c) >= 0;
    }

    static int? TranslateToNumber(char c)
    {
      if ("ABC".Contains(c))
        return 2;
      else if ("DEF".Contains(c))
        return 3;
      else if ("GHI".Contains(c))
        return 4;
      else if ("JKL".Contains(c))
        return 5;
      else if ("MNO".Contains(c))
        return 6;
      else if ("PQRS".Contains(c))
        return 7;
      else if ("TUV".Contains(c))
        return 8;
      else if ("WXYZ".Contains(c))
        return 9;
      return null;
    }
  }
}

using System;
using Android.App;
using Android.Content;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.OS;
using System.Collections.Generic;
namespace PhonewordApp
{
  [Activity(Label = "PhonewordApp", MainLauncher = true, Icon = "@drawable/icon")]
  public class MainActivity : Activity
  {
    static readonly List<string> phoneNumbers = new List<string>();

    protected override void OnCreate(Bundle bundle)
    {
      base.OnCreate(bundle);
      SetContentView(Resource.Layout.Main);

      var phoneNumberText = FindViewById<EditText>(Resource.Id.PhoneNumberText);
      var buttonTranslate = FindViewById<Button>(Resource.Id.buttonTranslate);
      var buttonCall = FindViewById<Button>(Resource.Id.buttonCall);
      buttonCall.Enabled = false; //禁用【拨号】按钮

      string translatedNumber = string.Empty;
      buttonTranslate.Click += (s, e) =>
      {
        translatedNumber = PhonewordTranslator.ToNumber(phoneNumberText.Text);
        if (string.IsNullOrWhiteSpace(translatedNumber))
        {
          buttonCall.Text = "拨号";
          buttonCall.Enabled = false;
        }
        else
        {
          buttonCall.Text = "播出号码：" + translatedNumber + "，单击确认！";
          buttonCall.Enabled = true;
        }
      };

      var buttonCallHistory = FindViewById<Button>(Resource.Id.buttonCallHistory);
      buttonCallHistory.Click += (sender, e) =>
      {
        var intent = new Intent(this, typeof(CallHistoryActivity));
        intent.PutStringArrayListExtra("phone_numbers", phoneNumbers);
        StartActivity(intent);
      };

      buttonCall.Click += (s, e) =>
      {
        phoneNumbers.Add(translatedNumber);
        buttonCallHistory.Enabled = true;
        // 当单击【拨号】时，尝试拨号
        var callDialog = new AlertDialog.Builder(this);
        callDialog.SetMessage("电话：" + translatedNumber + "，拨号吗？");
        callDialog.SetNeutralButton("拨号", delegate
        {
          var callIntent = new Intent(Intent.ActionCall);
          callIntent.SetData(Android.Net.Uri.Parse("tel:" + translatedNumber));
          StartActivity(callIntent);
        });
        callDialog.SetNegativeButton("取消", delegate { });
        callDialog.Show();
      };

    }
  }
}

<?xml version="1.0" encoding="utf-8"?>

<resources>

……

<string name="CallHistory">拨号记录</string>

</resources>

namespace PhonewordApp

{

[Activity(Label = "CallHistoryActivity")]

public class CallHistoryActivity : ListActivity

{

protected override void OnCreate(Bundle bundle)

{

base.OnCreate(bundle);

var phoneNumbers =

Intent.Extras.GetStringArrayList("phone_numbers") ?? new string[0];

this.ListAdapter = new ArrayAdapter<string>(this,

Android.Resource.Layout.SimpleListItem1, phoneNumbers);

}

}

}

……

using System.Collections.Generic;

namespace E01PhonewordApp

{

[Activity(Label = "E01PhonewordApp", MainLauncher = true, Icon = "@drawable/icon")]

public class MainActivity : Activity

{

static readonly List<string> phoneNumbers = new List<string>();

protected override void OnCreate(Bundle bundle)

{

……


var buttonCallHistory =

FindViewById<Button>(Resource.Id.buttonCallHistory);

buttonCallHistory.Click += (sender, e) =>

{

var intent = new Intent(this, typeof(CallHistoryActivity));

intent.PutStringArrayListExtra("phone_numbers",

phoneNumbers);

StartActivity(intent);

};


buttonCall.Click += (s, e) =>

{

phoneNumbers.Add(translatedNumber);

buttonCallHistory.Enabled = true;

// 当单击【拨号】时，尝试拨号

var callDialog = new AlertDialog.Builder(this);

callDialog.SetMessage("播出号码：" + translatedNumber +

"，拨号吗？");

callDialog.SetNeutralButton("拨号", delegate

{

// Create intent to dial phone

var callIntent = new Intent(Intent.ActionCall);

callIntent.SetData(Android.Net.Uri.Parse("tel:" +

translatedNumber));

StartActivity(callIntent);

});

callDialog.SetNegativeButton("取消", delegate { });

callDialog.Show();

};

}

}

}