C# で IE を操作

まずはとっかかり。
SMBCフレンド証券のログイン画面のフォーム要素を見つけて値を書き換える。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using mshtml;

namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            wb.Navigate("https://online.smbc-friend.co.jp/smbcfs-front/loginInformation.do");
        }

        private void wb_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
        {
            HtmlDocument doc = wb.Document;
            HtmlWindow win = doc.Window; // System.Windows.Forms.HtmlWindow
            HtmlWindowCollection frames = win.Frames; // System.Windows.Forms.HtmlWindowCollection
            if (frames.Count == 0)
            {
                System.Windows.Forms.HtmlElement loginForm = doc.Forms["loginForm"];
                if (loginForm != null)
                {
                    HtmlElementCollection usernames = loginForm.GetElementsByTagName("input"); // input タグ
                    HtmlElement username = usernames["username"]; // お客様コード
                    String value = username.GetAttribute("value");
                    Console.Out.WriteLine("c = " + value);
                    username.SetAttribute("value", "abc");
                }
                
                Console.Out.WriteLine("c = " + doc.Window.Frames.Count);
            }
            else if (frames.Count == 1)
            {
            }
            else if (frames.Count == 2)
            {
            }
            else
            {
            }
            //            Console.Out.WriteLine("c = " + doc.Window.Frames.Count);
        }
    }
}