Popular frameworks such as Selenimu, WatiN, and Coded UI all rely on the same underlying mechanism: invoking Internet Explorer’s COM interfaces and manipulating the HTML DOM. Instead of installing a third-party library, you can achieve the same result in a few lines of C# by referencing Microsoft’s own shdocvw.dll and mshtml.dll.

Why drive IE directly?

• Zero external dependencies—everything ships with Windows or Visual Studio.
• Fast prototyping: a minimal test harness can be written in minutes.
• Helps you understand what higher-level tools are doing under the hood.

Adding the required COM references

using SHDocVw;   // InternetExplorer, IWebBrowser2
using mshtml;    // HTMLDocument, HTMLInputElement, etc.

Launching and controlling the browser

var ie = new InternetExplorer
{
    Visible = true,
    Top  = 10,
    Left = 10,
    Height = 800,
    Width  = 1000
};

object missing = Type.Missing;
ie.Navigate("https://www.cnblogs.com", ref missing, ref missing, ref missing, ref missing);
Thread.Sleep(3000);

ie.Navigate("https://www.baidu.com", ref missing, ref missing, ref missing, ref missing);
Thread.Sleep(3000);

ie.GoBack();
Thread.Sleep(1000);
ie.Refresh();
Thread.Sleep(1000);
ie.Quit();

Inspecting the DOM

Use IE’s built-in F12 Developer Tools (or Firebug) to locate element IDs and attributes before scripting them.

Interacting with page elements

Example: perform a search on cnblogs.com.

var ie = new InternetExplorer { Visible = true };
object missing = Type.Missing;
ie.Navigate("https://www.cnblogs.com", ref missing, ref missing, ref missing, ref missing);
Thread.Sleep(3000);

var doc = (HTMLDocument)ie.Document;

var queryBox = (HTMLInputElement)doc.getElementById("q");
queryBox.value = "小坦克";

var searchBtn = (HTMLInputElement)doc.getElementById("btnBloggerSearch");
searchBtn.click();

Common build errors and fixes

If the compiler complains about Microsoft.CSharp.RuntimeBinder.Binder or missing dynamic support, add these references manually to the .csproj file:

<ItemGroup>
  <Reference Include="Microsoft.CSharp" />
  <Reference Include="System.Core" />
</ItemGroup>

After the references are added, rebuild the project and the errors disappear.